Downstream Oxygen Sensor and the Check Engine Light

My check engine light came on, and a trip to AutoZone for their diagnostic revealed the code for a bad downstream oxygen sensor. I replaced the oxygen sensor tonight. I’ve driven the car about 70 miles, but the check engine light is still lit. The area I live in requires emissions testing yearly in order to renew my car registration, and I will not pass if the codes still say my oxygen sensor is bad. How long until the check engine light goes off and the error codes clear out so I can pass emissions testing? My car is a 2005. Thank you in advance for your help.

How many miles are on this Grand Prix? You need to go back to AutoZone and have your codes read. They will be in a P 1234 format. Get any and all codes and post back.

have to turn off the engine light with the scanner.

Three drive cycles or just have the light turned off with the scanner.

After clearing the code, ALL of the monitors must run to completion

That could take several miles, depending on fuel level, coolant temperature, OP’s driving style, etc.

If too many monitors are incomplete, the tester may say the car’s not ready to be tested

I had an 05 nissian xterra, same issue, the check engine light would not go out, yet all the scan tools could not pick up any codes. The scan tools could not turn the light off either. I was blessed with emissions testing in my area aswell, I ended up calling the state and getting a waiver issued after I told them I was going to buy a 78 ford that burned oil.

I would tell you to keep driving it and after the drive cycles it will automatically go out, but that did not work in my case. It could be that there is still a problem.


Have you considered that the code was only readable by a factory-level scan tool?

My personal scanner is not a factory tool (it is a Solus Pro) . . . nevertheless, it can read factory codes that some of the cheap code readers and low-level scanners can’t

I also remember a GM truck with the check engine light on. The code was readable. My snap on scanner couldn’t clear it. The GM tech 2 couldn’t even clear it. Yet the Master tech scanner was able to clear the code.

Sometimes you just have to keep trying different scanners

If the light is still on, swing back by AutoZone and have them plug the scanner in. If it is still the same code, tell them that you bought the part from them and ask them if they will turn the light off for you. AutoZone’s policy is to NOT turn the lights off. They may do it for you since you bought the part from them and depending on whose behind the counter that day.

If there are other codes, post the exact code here and don’t let them try try to sell you anything.