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.