P0420 on 2000 Toyota Camry

Diagnostic code produces P0420 catalyst system efficiency below threshold-Bank 1. Probable causes are listed as follows: 1-air leak in exhaust before rear H02S 2-AF sensor error 3-Fuel system fault 4-faulty catalytic converter I've read posts about people replacing all of the above and the problems still exists. I have also read that there is a Toyota service bulletin in regards to this problem with my particular car. There is supposedly some sort of computer glitch which requires it to be updated. My car is over 80,000 miles and older than 8 years. I bought it used, it still falls under the used car places warranty, but i believe the toyota dealership is the only place to get the computer glitch fixed. If it has to be bought to the dealer to get fixed who is responsible for the bill? Also which of the possible causes do you think is responsible for the check engine light?

by in Mohegan Lake, NY on April 24, 2009
1 answer 1 comment
ANSWER by on April 25, 2009
The exhaust system/catalytic converters are different for California and federal cars. I assume yours is a Federal car. The front what many people call an Oxygen sensor is actually an air fuel ratio sensor and all though looks similar in construction is different in operation. The Air Fuel ratio sensor is difficult to test and people frequently do not test it correctly. It can be responsible for PO420 codes. The rear Oxygen sensor monitors the efficiency of the catalytic convertors and is located behind the rear Cat. Convt. It should have a relatively flat inactive voltage pattern when viewed on an oscilloscope, people need to look at that pattern before condemning a cat as being bad. If they pattern is very active the cat is bad. The inlet and out let temperature of the cats need to be looked at as another test. The rear O2 sensor measures both cat convectors, I have seen people replace one cat and hope it fixes the P0420 code. Your car's computer stores many problem parameters it saw when it illuminated the Check Engine Light. These codes stay in the memory of the computer until erased. Prior to just replacing parts ,you need to ensure what caused the failure is fixed. In the memory is stored Long and Short term fuel trim figures. Definitely see that these figures are +/- 3% to 5%. It is an indicator if the system is running too rich which can cause damage to the cat conv. In California we have to fit Original Equipment cat convt. which are expensive but more efficient that many after market catalytic converters.
COMMENT by on April 25, 2009
Ive heard that the computer need to be "flashed" is this true?
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