What the Check Engine Light Means
OBD II System
OBD II Malfunction Indicator Lamp (MIL)
When the ignition switch is initially turned on and the engine is not running, the malfunction indicator lamp lights for a bulb check. While the engine is running, the MIL will light only if there is an emissions-related concern.
The on board diagnostic (OBD) generation two (II) system continuously monitors all engine and transmission sensors and actuators looking for electrical faults, as well as values that do not logically (rationally) fit with other powertrain data. When certain operating conditions are met and a comprehensive monitor detects a failure that will result in emissions exceeding a predetermined level, the computer stores a diagnostic trouble code, and illuminates the MIL.
The OBD II system also actively tests some systems for proper operation while the vehicle is being driven. Fuel control and engine misfire are checked continuously, catalyst efficiency, exhaust gas recirculation operation, evaporative system integrity, oxygen sensor response, and the oxygen sensor heaters are tested once per trip when prerequisite operating conditions are met. The computer will illuminate the MIL if during these prerequisite operating conditions the system detects a failure that will result in emissions exceeding a predetermined level.
Whenever an engine misfire severe enough to damage the catalytic converter is detected, the MIL will blink on and off.
Once lit, the MIL will remain on until the vehicle has completed three consecutive good trips (three trips in which the fault is not detected). The MIL is also turned OFF when stored diagnostic trouble codes are cleared. However, the MIL will only remain OFF if the fault is successfully repaired.
Why timing belts need replacement
What is a timing belt?
Timing belts have replaced timing chains on many of today’s engines. Both belts and chains ensure that crankshaft, pistons and valves operate together in proper sequence. Belts are lighter, quieter and more efficient than chains.
Why replace the belt?
Like other components, timing belts wear out. Proper maintenance requires belt replacement at regular intervals–before they break.
Where are the belts located?
Timing belts are on the front of the engine protected by a plastic or metal cover.
When should belts be replaced?
When a timing belt breaks, the engine stops. Replace belts before this occurs. Most manufacturers provide a suggested service life and replacement schedule for this critical component.
How do I know if my car has one?
Your vehicle manual may tell you, but you should ask your technician–he will know for sure.
What is a “Free-Running” engine?
If the timing belt breaks on a free-running engine, the engine stops and you will need a tow to the repair shop. No mechanical damage occurs and the installation of a new belt is usually all that is needed to get you on your way.
What is an “Interference” engine?
If the timing belt breaks on an interference engine, mechanical engine damage occurs. It most commonly involves open valves being struck by pistons, resulting in the need for expensive repairs. In extreme cases, a replacement engine may be required.
Why cars need preventative maintenance
Why Preventive Maintenance
Manufacturers know that a properly maintained car will be more dependable, safer, last longer, and increase your satisfaction with their product. Car makers and owners also have a responsibility to make sure emission controls receive regular service and are functioning properly. Regular maintenance helps accomplish these goals by keeping your engine running efficiently and eliminating potential problems that may leave you stranded.
What’s in it for you?
- More Dependable Car
- A car that retains the “new car feel”
- Less chance of a costly breakdown
- A safer car for you and your family
- Doing your part for cleaner air
- A car worth more at trade in or sale
- An intact warranty
Manufacturer Maintenance Schedules
The manufacturer creates detailed maintenance schedules outlining specific operations to be performed on various components and systems. This is done at different mileage intervals to ensure proper operation and prevent premature wear. The manufacturer also indicates what services must be done to maintain the factory warranty and extended warranty.
What type of motor oil is recommended?
Use the type of motor oil specified in your customer’s owners manual. Most manuals say it’s okay to use a variety of viscosity grades depending on temperature conditions. Generally speaking, the following holds true:
- 10W-30 is best for all engines for year-round driving. 10W-40 is more popular in the aftermarket, but 10W-30 is actually a better oil because the additive package in it holds up better over the long haul. This is why General Motors does not recommend 10W-40 motor oils for any of its cars.
- 5W-30 is approved for most late-model four-cylinder, V-6 and V-8 engines on a year-round basis. It is not approved for many turbocharged or diesel applications, some high output V-8s, or applications involving driving at sustained highway speeds or towing in hot weather. It may not be the best choice for older, high mileage engines.
- 5W-30 is used as the factory fill oil on most new cars because it pumps through the engine more quickly after start-up (important for keeping overhead cams properly lubed). It also makes cold weather starting easier and reduces fuel consumption.
- Straight viscosity oils have limited temperature ranges and lack the versatility of multiviscosity oils. They can be safely used as long as their temperature limits are observed.
- Special multiviscosity oils such as 2OW-50 are typically formulated for racing or severe duty applications such as towing.
- Synthetics are a good alternative for any of the above because most provide extended temperature protection and service life.
High Mileage Vehicle Inspection and Maintenance
Fixing Your Present Vehicle Saves Money
Most of us want to get the most for our motoring dollar. One of the best ways to do this is extending the life of your current vehicle. With new car prices in the United States averaging well over $10,000, money invested in keeping your existing vehicle in good shape could save you hundreds–even thousands–of dollars a year. When you consider the true cost of buying a new car (price of the car, sales tax, license and registration fees, insurance), it is not difficult to justify investing a few hundred dollars to repair your present vehicle.
Safety and Scheduled Maintenance
The safety aspect of properly maintaining your vehicle, especially when it has high mileage, should not be overlooked. Failing brakes, exhaust leaks and other problems can be prevented by following sound car care practices.
Unfortunately, most manufacturers only provide maintenance guidelines for the first 100,000 miles or so. Clear procedures for maintenance beyond this mileage do not exist. At best, manufacturers provide interval service schedules, such as every 15,000 miles. These schedules should be followed whenever possible. By doing so, you can reasonably expect thousands more satisfactory miles from your vehicle.
High Mileage Inspection and Evaluation
If your vehicle has passed the 100,000 mile mark and you want to significantly prolong its useful life, it is time to have it thoroughly evaluated by a professional automotive technician who can recommend needed repairs or service. This facility is equipped to perform this service. We employ technicians who use factory-level information detailing your vehicle’s service requirements.
Our high mileage inspection and evaluation goes beyond cursory “once-overs” and is designed to get to the root of potential problems. Ask your service advisor or technician to show you exactly what is involved in this service. He or she will be happy to go over the evaluation form with you before you okay the inspection and provide you with a comprehensive estimate for any work recommended as a result of your vehicle’s checkup. They will tell you about repairs that are necessary today, and also alert you to items that are potential problem areas you may want to address today for more trouble-free miles tomorrow. Naturally, you make the decision as to what work is actually performed.
Working together, we can add years to the life of your car or truck.
What should a complete tune-up include
- Electronic ignition, computerized engine controls, and electronic fuel injection have eliminated many adjustments that were once part of a “traditional” tune-up. Most would agree that a tune-up today is a preventive maintenance service and engine performance check.
- Call it what you will, a complete tune-up should combine elements of preventive maintenance, adjustment and performance analysis. One of the main reasons people bring a vehicle in for a tune-up is because they are experiencing some kind of driveability problem.
- Things like hard starting, stalling, hesitation, misfiring, poor fuel economy, or lack of power are seldom cured by a new set of spark plugs and a few turns of a screwdriver. Every tune-up should include a comprehensive performance check to verify that no driveability problems or trouble codes exist.
- Taking into account longer service intervals and reduced maintenance requirements of today’s vehicles, a tune-up is probably only necessary every 30,000 miles, or once every two to three years. This is altered when a driveability or emissions problem arises that requires diagnosis and repair.
- The best guide to tune-up frequency is probably the recommended spark plug replacement interval in a vehicle’s owners manual.
- Our list of items that should be included in a “complete” tune-up include:
- Replace spark plugs
- Replace rotor
- Check distributor cap (replace if necessary)
- Check timing (adjust if necessary)
- Check ignition wires (replace if necessary)
- Check ignition performance (firing voltage and ignition patterns)
- Check idle speed (adjust if necessary)
- Check choke (carbureted engines)
- Clean fuel injectors
- Check compression and/or power balance (identifies bad fuel injectors as well as compression problems)
- Check manifold intake vacuum (reveals exhaust restrictions)
- Check battery/charging voltage
- Check vehicle computer for trouble codes
- Install new air filter
- Check all vital fluid levels (engine oil, transmission fluid, coolant, brakes, power steering)
- Check belts and hoses
- Check safety items such as lights, wipers, tires (including inflation pressure), horn, etc.
Is it better to clean or replace dirty fuel injectors
Injectors include a precision-ground needle valve and are controlled by an electro-magnetic solenoid that is turned on and off by an electric control unit. Fuel is injected only during the “on” time and is metered by the size of the opening, duration of “on” time, and fuel pressure.
Try cleaning them first. If this is not successful, they must be replaced.
Because of their construction, fuel injectors tend to “gum up” after 15,000 to 30,000 miles of driving. Fuel spraying from the injector must pass through a very small opening in the discharge nozzle. This is necessary to create a cone-shaped spray pattern that breaks the fuel up into a fine mist for proper atomization.
Some newer style injectors are more clog resistant than their predecessors, but all are vulnerable to some extent.
Every time the injector sprays fuel, a small amount remains in the nozzle. As it evaporates, it leaves behind a wax-like residue that forms hard varnish deposits.
The rate at which deposits build up depends on the quality of gasoline burned, whether or not the gas has detergent in it (and what kind), and the number of thermal cycles the engine experiences per miles driven. Short-trip driving builds up deposits more quickly than continuous driving.
As deposits build up in injectors, they restrict the discharge orifice and break up the normal cone-shaped spray pattern. The spray pattern may develop “legs” (streamers of unatomized fuel) or turn into a continuous stream of unatomized fuel like a fire hose.
Liquid fuel does not burn as efficiently as atomized fuel, so it has a “leaning effect” on the air/fuel mixture. Accumulated deposits in the discharge orifice also restrict the total amount of fuel delivered per squirt, which further compounds the leaning effect. This can result in the appearance of driveability problems such as hard starting, hesitation, poor fuel economy, loss of power, and elevated exhaust emissions.
An engine with dirty injectors will usually show a wide variation in RPM between cylinders when doing a power balance test. There will also be a lot of variation in peak firing voltages between cylinders on a scope.
For do-it-yourselfers, there are two options – use a fuel additive to clean the injectors, or buy a can of pressurized solvent that’s designed for on-car injector cleaning. Fuel additives can only do so much, so badly-clogged injectors usually need to be pressure flushed with solvent.
With on-car cleaning, pressurized solvent is run through injectors to flush out deposits. To do this, the fuel pump is temporarily disconnected so solvent can be fed directly into the test valve fitting on the fuel rail.
When the engine is started, the solvent becomes the temporary “fuel supply” while injectors are cleaned.
The resulting improvement in performance is usually quite noticeable. But on-car cleaning doesn’t always do the trick, especially if an injector is badly plugged.
Unless injectors are removed and tested, there is no easy way to spot marginal injectors (those with defective spray patterns) or ones that don’t deliver as much fuel as the others (mismatched injectors can reduce horsepower and increase emissions).
Off-car cleaning involves more work, but results are often worth it. For one thing, injectors that don’t respond to on-car cleaning can often be restored to like-new performance with off-car cleaning.
Some available cleaning equipment can reverse flush injectors, doing a thorough cleaning job. Most off-car cleaning equipment also allows the mechanic to observe and measure injector flow patterns so bad ones can be identified.
Flow rating also allows injectors to be more closely matched for improved engine performance.
Is it better to rebuild or replace a carburetor or throttle body
If all the carburetor needs is cleaning and adjusting, then a kit will usually do the trick. A kit is also an option if the carburetor needs a gasket, diaphragm, needle valve, check valve, or other component commonly included in a kit.
Floats, choke housings and choke pulloffs are usually sold separately, but are relatively easy to replace if defective. Faulty or misadjusted chokes and floats probably account for more carburetor problems than anything else.
Most carburetors today have molded foam floats rather than hollow brass floats. Some import carbs have hollow plastic floats. If a hollow float develops a leak, it will fill with fuel and sink, causing the carburetor to flood.
The solid foam variety can absorb fuel over a period of time. That’s why the float should always be weighed when the carburetor is rebuilt. A heavy float will make the fuel mixture rich. Replace heavy floats.
Kits are not for everyone. It takes a fair amount of know-how to properly rebuild and adjust a carburetor. It also takes a lot of time to disassemble, clean, inspect, and reassemble a carburetor. Many professional installers, as well as do-it-yourselfers, prefer to replace a troublesome carburetor rather than to try to rebuild it with a kit.
There are some carburetor problems that cannot be fixed by a kit or by replacing faulty components. Wear around throttle shafts or warpage in the carburetor body or throttle plate can create vacuum leaks that foul up fuel metering. The only option here is replacement.
Most rebuilt carburetors are sold on an exchange basis, so it’s important to make sure that the exchange carburetor is complete (all external parts intact), has not been disassembled, and is correct for the application.
If a base gasket is not included with the replacement, be sure your customer gets one before he leaves. Your customer may also need new fuel hose, fuel filter, and air filter to complete the installation.
Because there are many small components included in a TBI kit, it is important to inspect each kit to verify that everything is included. Installers must pay close attention to the kit when assembling the unit to be sure small parts are placed in their respective positions.
What are the rules for replacing catalytic converters
In a closed loop emissions operation, pump air is injected downstream between reduction and oxidation catalysts when the engine is warm.
Three-way catalytic converters contain both catalysts in a single housing, with an air inlet between the two converters.
Original equipment converters on new cars and light trucks are currently covered by an eight year/80,000 mile emissions warranty. Motorists can return to the new car dealer for free replacement as long as the converter is covered.
The customer can choose to have an independent repair garage replace the converter at his own expense if it is still under warranty. Once the vehicle is out of warranty, he pays to have it fixed no matter where he takes it.
The converter should go at least 100,000 miles on most late model vehicles. Trouble is rare unless the converter has been lead fouled (by using leaded gasoline), damaged by overheating (often due to unburned fuel in the exhaust from a misfiring spark plug or leaky exhaust valve), or removed.
If the vehicle has flunked an emissions test and the cause is determined to be a bad converter, or if the converter is clogged, damaged, lead-fouled, rusted out, physically damaged or missing, it is okay to replace it. Federal law prohibits aftermarket garages from replacing converters as long as they’re under the five/50 emissions warranty, unless any of the previously-mentioned reasons exist for replacement.
The shop must first document the reasons, along with the vehicle’s odometer reading, and have the customer sign it before the converter is replaced. The shop must keep the old converter for 15 days and the paperwork for six months. The replacement converter must be the same type as the original (two-way, three-way or three-way plus oxygen), be EPA-certified, and be installed in the same location as the original.
Aftermarket replacement converters meeting EPA requirements must have a minimum lifespan of 25,000 miles, and include a five year/50,000 mile warranty covering exterior shell and welded pipes against defects in materials and workmanship.
Used converters are no longer allowed unless the supplier can certify the converter is still capable of cleaning up 50% of the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions within two minutes of start-up, and 75% of the HC and CO emissions within 200 seconds.
All approved replacement converters are required to carry a permanent label that identifies the type of converter (N for new, U for used), a code number issued to the manufacturer by the EPA, an application part number, and a manufacturing date.
How often should oil and filter be changed
Change oil and filter often enough to protect the engine from premature wear and viscosity breakdown. For most cars and light trucks, the standard recommendation is to change oil and filter every six months or 3,000 miles, whichever comes first.
Most late model owner’s manuals say that except for “Severe Service” applications, oil change interval can be safely stretched to once a year or every 7,500 miles, with filter changes at every other oil change.
When auto makers make such recommendations, one assumes they are based on extensive durability testing. After all, auto makers themselves would have to bear the warranty costs should their maintenance recommendations prove inadequate.
Except for Chrysler’s 7/70 powertrain warranty, and a few others that go up to 5/50 or 6/60, most new car powertrain warranties don’t go beyond 3/36. So where’s the risk? There isn’t any.
With proper maintenance, there is no reason an engine shouldn’t go 100,000 miles or more without developing a thirst for oil. That is why most oil companies, as well as aftermarket service professionals, recommend changing oil and filter every six months or 3,000 miles.
They also make such recommendations because many motorists are not aware that they should follow the “Severe Service” maintenance schedule in their owner’s manual, calling for oil and filter change intervals of three to six months or 3,000 miles. Severe service (as defined by auto makers themselves) includes:
- Making frequent short trips (less than five miles)
- Making frequent short trips (less than 10 miles) when temperatures are below freezing
- Driving in hot weather stop-and-go traffic
- Extensive idling and/or low speed driving for long periods of time (taxi, police, door-to-door delivery, etc.)
- Driving at sustained high speeds during hot weather
- Towing a trailer
- Driving in areas with heavy dust (gravel roads, construction zones, etc.)
Protective additives in a motor oil do not hold up as well under such driving conditions for several reasons. If the engine is not running long enough to get the oil hot, condensation and fuel vapors will not boil off. Contaminants will accumulate in the crankcase, leading to formation of corrosive acids and sludge.
Excessive idling and high operating temperatures from towing and high speed driving during hot weather accelerate viscosity breakdown. Exposure to dust can put dirt particles in the crankcase.
The filter also needs to be changed every time for two reasons. Today’s pint-sized filters do not contain as much filter material as their quart-sized counterparts. The filter contains dirty oil that can contaminate fresh oil added during an oil change.
Considering what four quarts of oil and a filter cost, versus the cost of replacing an engine, it is better to change oil and filter a little more often than might be absolutely necessary rather than risk not changing it often enough.
The crank seal has been replaced but it still leaks
Try a crankshaft repair sleeve. When a groove is worn in the crankshaft seal area, a new seal will not have a smooth surface to seal against. It will either leak immediately or wear prematurely. Replacing the crankshaft will solve the problem, but it is an expensive fix. An economical and effective alternative is installing a slip-on repair sleeve.
What things should be included in a complete valve job
Everything needed to restore a cylinder head to like-new condition, including basics such as:
- Cleaning cylinder head and valve train components
- Inspecting head for cracks, leaks, warpage, or other damage
- Inspecting valves, seats, springs, guides, and other valve train components for wear and damage (and replacing parts that cannot be reused)
- Grinding or cutting valves and seats
- Restoring valve guides by knurling, relining or replacing, or reaming guides and using valves with oversized stems
- Checking installed valve stem height, spring height and tension, etc., and reassembling the head with new valve guide seals and any other required parts
- Resurfacing head to assure flatness and a proper seal
- The following “extras” might be required, especially on overhead cam aluminum heads:
- Repairing leaks or cracks
- Overhead cam line boring
- Repairing threads
- Replacing seats
There is no such thing as a “standard” valve job. Every job is different. An overhead cam aluminum head may require a lot more time and effort than a cast iron head off a pushrod engine. There is often no way to tell what a head will need in terms of repairs until it has been cleaned, disassembled and inspected.
Exhaust valves and springs often need to be replaced. Valve guides and/or seats may have to be replaced. The head may be warped or cracked, requiring additional repairs. The list of things included in a “complete” valve job will vary from job to job.
What kind of maintenance is recommended for the cooling system
Vol. Per Cent Coolant
Boiling Point °F (at 0 psig)
Freezing Point °F
Replacing coolant on a regular basis will prolong the life of the radiator and other cooling system components. Most new car maintenance schedules call for coolant changes every three years or 50,000 miles. Many professional mechanics consider that too long and recommend every two years or 24,000 miles.
There are some who argue that annual coolant changes on late model vehicles with bimetal engines (aluminum heads/iron blocks) and/or aluminum radiators is a good idea.
It does not really make much difference how often the coolant is changed as long as it is changed before losing its corrosion resistance. Antifreeze is made of ethylene glycol (which never wears out) and various additives (which do wear out).
Some additives provide “reserve alkalinity” to neutralize internal corrosion before it can start. As long as the coolant is changed before its reserve alkalinity is depleted, the cooling system should be no worse for the wear. If you wait too long, the result can be expensive internal corrosion in the radiator, heater core and engine.
How can you tell when it is time to change the coolant? The only way to know if the coolant still has adequate corrosion protection is to test it. By dipping a test strip in the coolant and noting its color change, you can determine coolant condition and whether or not it is time to replace it.
When coolant is changed, the system should be reverse flushed rather than simply drained. This helps dislodge and remove accumulated debris and debris in the system. It also removes old coolant that would otherwise remain in the engine block.
Use of a cooling system cleaner is not necessary unless the system has been badly neglected and is full of lime deposits.
The cooling system should be refilled with a 50/50 mixture of ethylene glycol antifreeze and clean water. This provides freezing protection down to -34 degrees F and boil-over protection to 265 degrees F.
When coolant is changed, inspect belts and hoses. Make a visual inspection for leaks. Pressure test radiator and cap. Check operation of heater and defroster.
The thermostat does not need changing unless it has been causing trouble or the engine has severely overheated. If a thermostat is replaced, it should have the same temperature rating as the original. This is extremely important on late model vehicles with computerized engine controls. Fuel, ignition and emission functions are all affected by coolant temperature.
What can make an engine overheat
Overheating is caused by anything that leads to a loss of coolant, prevents the cooling system from getting rid of heat, or causes excess heat in the engine itself:
- Coolant leaks (water pump, radiator, heater core, hoses, freeze plugs, head gasket, engine internal).
- Weak radiator cap (does not hold rated pressure and allows coolant to boilover). Pressure test the cap to check it out.
- Cooling system clogged (deposits built up in radiator or in engine due to maintenance neglect or use of hard water). Use a cleaner, then reverse flush the system to clean it out. A badly-clogged radiator may need to be rodded out or replaced.
- Thermostat stuck shut (replace).
- Inoperative electric cooling fan (check fan motor, relay and temperature switch for correct operation).
- Bad fan clutch (replace if slipping, leaking or loose).
- Missing fan shroud (reduces cooling efficiency of fan).
- Slipping fan belt (tighten or replace).
- Too low or too high a concentration of antifreeze (should be 50/50 for best cooling).
- Bad water pump (impeller eroded or loose – replace pump).
- Collapsed radiator hose (check lower hose).
- Debris in the radiator (remove bugs and dirt).
- Late ignition timing (reset to specs).
- Restricted exhaust system (check intake vacuum readings and inspect converter, muffler and pipes).
- Radiator and/or fan undersized for application (increase cooling power by installing larger radiator and/or auxiliary cooling fan).
Battery keeps running down
Is it the Battery, Alternator, or Voltage Regulator?
It could be any one of the three, or an undetected voltage drain caused by a trunk light, underhood light, or glovebox light that does not go out when the lid is closed.
An alternator is based on the rotation of a magnet inside a fixed-loop conductor. The output circuit and the field circuit make up the automotive charging system.
The first thing that should be checked is the battery state of charge. If it has a built-in hydrometer (charge indicator), a green dot means the battery is 65% to 75% charged and okay for use or further testing.
If the charge indicator is dark, the battery is less than 65% charged and needs to be recharged and load tested.
On 1985 and later model Chrysler vehicles, the charge indicator on some batteries also contains a red dot which shows if the battery is less than 50% charged.
If the charge indicator is clear or yellow, the level of electrolyte inside the battery has dropped too far to give a reading. It also means the battery will need to be replaced soon. Once water level drops below the top of cell plates, they dry out and lose their ability to hold a charge.
Never attempt to jump start or charge a battery with a low electrolyte level. It may explode.
The state of charge of a sealed top battery without a built-in charge indicator can be determined by measuring its open circuit (no load) voltage:
Open Circuit Voltage
State Of Charge
11.7 or less
A low charge level does not mean anything is wrong with the battery or charging system, it simply means the battery is low and needs to be recharged.
Performing a load test would be the next step. This checks the battery’s ability to deliver current. The battery must be at least 65% charged before load testing. If not, a good battery may fail the test.
A conventional load test is performed with a carbon pile battery tester. The load created by the carbon pile is adjusted according to the battery’s cold cranking amp (or amp/hour) rating. The carbon pile is usually set to one half the battery’s CCA rating (or three times its amp/hour rating).
Temperature compensation is also important because a cold battery puts out fewer amps than a warm one. The load is then applied to the battery for 15 seconds while voltage output is observed. If voltage remains above 9.6 volts, the battery is good. If it drops below 9.6 volts, the battery can be recharged and retested, or given a three-minute charge test.
A three-minute charge test checks for a sulfated battery. Slow charge the battery at 40 amps for six minutes, then check voltage across the terminals with the charger on.
If the voltage is above 15.5 volts, the battery is not accepting a charge. Slow charging for 20 hours can sometimes reverse the sulfated condition, otherwise the battery is junk.
If the battery check is okay, the next item to check is the charging system. A properly working system produces a charging voltage around 14 volts at idle with lights and accessories off (refer to a shop manual for exact charging specs).
When the engine is first started, charging voltage should rise quickly to about two volts above base battery voltage, then taper off and level out at the specified voltage.
Exact charging voltage will vary according to battery state of charge, load on vehicle electrical system, and temperature. The lower the temperature, the higher the charging voltage. The higher the temperature, the lower the charging voltage.
On a GM application, for example, accepted voltage charging range is 13.9 to 14.4 volts at 80 degrees F. At 20 degrees F below zero, charging range is 14.9 to 15.8 volts. At 140 degrees F, the charging voltage is 13.0 to 13.6 volts.
Charging output can also be checked with an adjustable carbon pile, voltmeter and ammeter. The carbon pile is attached to the battery and adjusted to obtain maximum output while the engine is running at 2,000 rpm.
If charging voltage is low, the alternator or voltage regulator could be faulty. To find out which component is bad, a procedure called “full fielding” can be used to bypass the regulator.
If the alternator produces the specified voltage or current output after full fielding, the problem is in the regulator (or wiring) not the alternator.
The exact procedure for full fielding an alternator varies from vehicle to vehicle depending on how the alternator is wired. Basically, the regulator is bypassed by connecting a jumper wire between the field (FLD or “F” terminal) and battery positive (BAT) terminal on the alternator.
On older GM applications with Delco integral regulator alternators, inserting the tip of a screwdriver through the D-shaped hole in the back of the alternator full fields the unit.
Either voltage or current output can be compared against manufacturer specs to determine if the alternator is functioning at full capacity. Generally speaking, alternator output should fall within 10 amps or 10% of its rated capacity at 2,000 rpm.
For several reasons, it is important to follow full fielding test procedures exactly. If only one diode or stator winding is bad, for example, the alternator may still make enough electricity at high rpm to keep the battery charged, but not at idle or low speed. The alternator and/or regulator can also be damaged if the wrong test procedure is used.
On Chrysler externally regulated alternators, for example, you do not apply voltage to the “F” terminal. This system is full fielded by grounding the green wire at the regulator connector. On externally regulated Ford alternators, the alternator is full fielded by disconnecting the four-wire connector from the regulator and jumping across the “A” and “F” terminals.
If charging output goes up when the regulator is bypassed by full fielding, but otherwise fails to produce voltage, check the regulator for a poor ground. This is especially important on Ford and Chrysler systems. Poor or open wiring connections between alternator and regulator can also cause a charging problem.
A slipping fan belt is one of the most common causes of under charging. A fan belt that holds at idle or low rpm may slip when the alternator is under load. Glazed or burned streaks on the belt are an indication of slipping.
If the battery and charging system are okay and the battery keeps running down, check for a voltage drain somewhere in the electrical system. To isolate the cause, remove one of the battery cables and connect a volt meter or amp meter between it and the battery.
A voltage drain will cause a reading on the meter. Disconnect fuses one by one until the circuit is found that causes the reading to disappear.
On-board electronics such as the computer, an electronic clock, etc., will draw a few milliamps all the time, but should not be enough to run the battery down unless the vehicle is not driven for long periods of time.