well my coil went bad and ended up clogging one of my cats so i replaced the coil and the 2 cats. i had a bad exhaust leak after so i tried to heat the flange and hammer it flush with the other, it didnt work. anyways that day i drove home and the light went on. checked the codes it was 27 and 29. both to do with o2 sensors. i took the sc400 to the shop and got the flange cut off and welded so there isnt a exhaust leak anymore thinking the problem was fixed i erased the code and drove home. as soon as i got on the highway maybe 5 min into my drive they came back. what could be wrong? any ways to check if the sensors are bad?

thanks

jimmy

 

The sensors aged with the cats/maf etc and once you changed the cats it threw them off, the worn sensors showed their age.


OR, did you do a full reset of the ecu, leaving the battery cable disconnected for at least 30 min?

 

i just left the battery off for about 5 min. if i leave it off for over 30 min, and the check engine light comes back then most likely the sensors are bad?

 

I've only had success resetting the ECU on my 400 for no less than 30 min. If the light still comes up, clean your maf, and i believe there is a test you can do to test for proper resistance from the O2 sensors. Honestly with as old as our cars you should just replace them anyway. Universal Denso's only cost about 45 a piece and you wire them in.

I had no codes and changed the O2 sensors and cleaned the MAF just because. BIG DIFFERENCE

 

what do you use to clean the maf?

well i reset the ecu and the lights went out for a while, about 10 min drive. so i parked it. next moring i started up and the light went on instantly. drove to work, shut it off and started it up within 10 min and no light. drove for 10 min and it came back.

would the light come on for a small exhaust leak?

thanks

 

I cant remember the name of the MAF cleaner i used but, go to advanced and get only the most expensive stuff, Its made by an electronics company. The name of it is like three letters lol.

No, not from an exhaust leak, i have one that is fairly large, but no code.