oxygen and catalyst sensors not ready - won't pass emmissions

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Just had the charcoal canister replaced, check engine light is now off, but oxygen and catalyst sensors are showing as 'not ready' and vehicle will not pass emissions. Car has been driven over 200 miles and sensors still show 'not ready' Battery was replaced last summer. Will the 'drive test' solve this issue ?? and does the fuel tank level need to be as indicated in the drive test (seems like the fuel level is critical for EVAP only)?

boggs32 in Aliquippa PA

Sep 3, 2014

3 Replies

Popular Answer

studynewson Jul 30, 2016

It seems ironic that to get a car to pass environmental protection standards, you are forced to drive and pollute the environment in excess of 200 miles. For many people that can be the amount of driving they do an entire year.

camryloveon Sep 3, 2014

Did you clear the code(s) after the canister was replaced? Scan for any pending codes and if there are any, address them first. You can try disconnecting the battery and going for a test drive. Hopefully the monitors will reset. It's not about the miles driven, there are certain parameters that the computer needs to check before showing 'ready.'

boggs32on Sep 3, 2014

thanks - codes have been cleared and there are no pending codes. Does gas tank need to be at a certain level?

camryloveon Sep 3, 2014

I don't think so. You can try filling up the gas tank and driving until hopefully the monitors reset.

Reply in Thread

cardocIIIon Sep 4, 2014

I usually expect to see a 1999 pass with two monitors not ready as the cut-point to one monitor incomplete is 2000. Even so, the progressive nature of OBDII causes certain tests to be blocked from running until the correct conditions are achieved. Things like getting the engine to full operating temperature and be driven at speed for a given period of time come into play and are part of the drive cycle that has to get completed. One of the strategies to solving this issue is to take one of the tests that isn't completing, such as the O2 sensors. Look at what trouble codes could be set if the test failed and you will find the code enabling criteria listed. The code enable criteria will essentially list what needs to be checked to see what is blocking the test from running. Once that is identified and dealt with, then we could look further if necessary. I'd start with the O2 system and their heater circuits. The O2's have to test and pass for the catalyst test to run. I'm out teaching in New York right now and will be back in the shop this weekend. If you would like us to investigate this, call the shop number and we can schedule it in.

boggs32on Sep 4, 2014

Thank you for the informative answer. I did find out today that a 1999 will pass with 2 monitors ready, I obviously did not know that. Now this a.m. check engine light came on again, checked it and it says bad oxygen sensor, cleared it and drove it, checked it and had 4 incomplete, drove it again and still have 3 incomplete EVAP, Oxygen and Catalyst. Understand the oxygen and catalyst being related per your explanation, but don't understand the EVAP at all as I just replaced the charcoal canister. Thank you for your time.

cardocIIIon Sep 4, 2014

Depending on a manufacturers strategy for confirming if the evaporative system purge valve can draw vapors, the O2 sensor system might need to be tested by the onboard computer first. A lot of vehicles watch for a shift in the fuel trim when the purge valve is turned on and off confirming that flow took place. If the O2 sensor cannot be trusted to be accurate, (the O2 sensor failed code) that could block that portion of the evaporative monitor and that means that it would not complete. BTW, stop clearing codes. That is actually making it harder to solve at this point because you would be erasing other background information that would help give a technician direction towards solving this.

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