check engine 0420 code
 

2001 camry le came up with a 0420 check engine code. Indicates problem with O2 sensor. Would it be the sensor before or after the cat. converter? I have also heard possible failing cat converter, but many suggest changing the O2 sensor first. Help and thanks!

RE: check engine 0420 code
 

P0420 usually means there is a problem with the 02 (A/F) sensors, their circuits (wiring) or the CAT.

The exhaust system has 02 (A/F) sensors before and after the CAT. The signal outputs from the two sensors are compared by the ECU to determine the efficiency of the CAT. If the signals are of the same amplitude, the ECU triggers the code. Meaning there is a problem with either of the sensors, their wiring or the CAT is operating below efficiency.

There are specific trouble codes for the sensors but none to indicate the CAT is bad. If no other codes are indicated then running down the problem is harder without doing some kind of diagnostics. The Toyota dealer has their diagnostic reader which should be able to tell without guessing exactly what sensor or if the CAT is bad.

Keep in mind the federal government requires the CAT to be warranted for 8 years or 80K.

2000 Camry Code P0420
 

I just acquired a 2000 Camry 2.2L, 5 speed manual with 71,000 miles. Shortly after I got the car, the check engine light came on. I had the code pulled at Auto Zone and it was P0401, EGR system. Not having time to do the repairs myself, I took it to the local Toyota dealer who diagnosed the problem as EGR valve and VSV valve. $680.00 later, both are replaced.

Now, and immediately after the EGR system repair, the car is now throwing another code P0420, which as I understand indicates either a bad cat converter, bad AF sensor, exhaust system air leak or fuel system problem. Mind you this code did not exist before the EGR repairs.

What most likely happened. Did the dealer muck something up? My greatest fear is I take it back to the dealer and they will tell me it needs a new Cat. Sorry, I'm not buying that at only 71,000 miles. Where else could I take the car for a definitive diagnosis?

BTW, the car runs fine and there is no evidence on the spark plugs of oil or any other fuel system issue. After the P0420 code appeared the first time, it was cleared and a day later is back again.

It is likely a problem with the upstream AF sensor. It is quite common.

JJ

Thanks for the reply JJ. By upstream, can I assume that is the O2 sensor in front of the cat?