What is your question?
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What is your question?
I have P0420. How do I determine if the fault is the rear 02 sensor or the cat. The way I understand this the rear 02 sensor waveform is supposed to "mirror" the front 02 sensor waveform, but at a reduced amplitude. Also. the rear 02 sensor amplitude is supposed to be below 650mVdc max. If either of these conditions can be verified the cat has to be bad if I get P0420 since the 02 is apparently working correctly. Is this correct or am I confused on how this works.
3 Replies
google catalytic converter temperature and use an inferred thermometer to measure the temp front and rear of the cat , beat on it do you hear a rattling coming from the inside? yes= sure sign of failure . swap o2 sensors front/rear left/right if problem follows o2 the o2 is suspect. p0420 is a generic code you need a more definite code(manufacturers fault code) to do the o2 swap.
The Easy way to do this is if the front and rear o2 sensors mirror each other in terms of amount of fluctuation and the outlet temperature of the Cat is at or lower than the inlet temp the cat is faulty. ( we use an infrared thermometer and on a healthy cat the outlet temp can be as much as 200 degrees higher). Hope this helps!
For your 98 Town Car, P0420 and P0430 are nearly always reflective of internal catalyst inefficiency, resulting in replacement of the affected converter(s).