my check engine light is on. I have replaced the oxygen sensors twice with Firestone and the light is still on. How can I reset it as my registration is due with a smog check? Firestone says the sensors are new and cannot be bad two times in a row.
Yeah, get a code reader (or go to AutoZone) and get the code for yourself. I wouldn't go back to Firestone, especially if they're not diagnosing the problem correctly. If they're just throwing new O2 sensors on when the light could very well be something else unrelated, I wouldn't trust them with anything more than putting on tires.
Go to a real mechanic...anywhere but that Firestone.
Normally it should be expected that a PROFESSIONAL repair shop should not fall into "parts changing" method of trouble shooting. Shame on them for the first swap. Shame on YOU for the 2nd. Regardless. Listen to them as it's very likely the cause of the DTC code is something else.
A PCM reset can be easily done by disconnecting the battery. However this won't help you pass a smog test as the readiness tests will NOT be complete. Best to find out what the full DTC is and work through a real repair. There are 1,000's of DTC codes and they each have a story to tell.
Plus... it could very well be there is something else wrong, and that the O2 sensors are fine. Depends on the code thrown.
Mine is prone to toss code 1233 often, which indicates the fuelpump has no power. Which happens if you try to start the car when the aftermarket alarm blocks the start by among other things cutting power to the fuelpump. The error is not wrong, it's exactly what's going on, but it's registered as an error, and it will not clear on its own, unless I clear it using the reader.
I'm not sure why the O2 sensors were changed (unless a prior readout already indicated they were the cause of a problem). There might have been other codes, or the fact that the O2 sensors now finally provide a correct reading may trigger another code somewhere else that was masked by the O2 not working properly. No way to know for sure, unless it's read out.