: I replaced all 4 O2 sensors on my 1996 GMC 5.7L Yukon. My scan tool shows "Sensors not ready to communicate or available" for #2 &
#4 ( downstream. #1 & #3 are fine and reading.)
The code P0420 indicates that the catalytic converter is not functioning efficiently. This could be because the cat is damaged or the engine is not running very well and the cat cannot keep up with the emissions. You should ensure that the spark plugs and ignition components are in top shape before replacing anything else. If a compression check reveals a low cylinder, you will not be able to prevent this code as even a new cat cannot keep up with a dead miss. If the state of tune and the compression is good, then you'll likely need a cat.
I've posted the drive cycle just so you know what to do when you have resolved the code.
Do not leave the key in prior to the cold start or the heated oxygen sensor diagnostic may not run.
This code means your catalytic converter is below efficiency status .the o2 sensors will not fix this problem ,the ceramic in the converter is broke down ,so the converter it self is the problem.So many people think that it is a bad o2 but it is the converter!
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The code is P0420 but when you run a sensor check on the scanner that is the message I get
You'll simply need to drive it further. There is a drive cycle to reset the readiness monitors. I will see if I can dig it up.
what are the code #s
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