Hi. Is it possible for the O2 sensor to be wonky (I swear this is a real word), but the check engine light not come on (or the ECU not throw a code) Thanks.

 

i believe it is possible. i know you can unplug it and not get an error code.

 

Its impossible to get that check engine light on. I replaced my o2 sensor because it was a bit lazy and the voltage took a good while to start cycling. I replaced it with a Bosch unit and its not lazy anymore. But yes you can have a sensor problem and the CEL won't come on.

 

I've checked my CEL 3 times to make sure its not burnt out, lol.

Other gens always biatch about theirs being on, I guess thats one more good thing about 3rd gens, hehehehee.

 

Is it possible for O2 sensor to be bad even when it passes the ECU test in Mode 2. Both lights flash on and off. My car runs rich barely passing HC emissions testing and building up carbon on all plugs. Car runs well other than rich. Plugs, distibutor cap & wires have been changed recently. Others on the site have said just change the sensor, but I don't want to change what I believe is good (passes test).

 

if the o2 has over 10 years or 60k on it. Replace it