Question about 1995 GMC Sierra C1500
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Posted on Jan 02, 2017
SOURCE: 02 sensors not ready
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.
Posted on May 14, 2009
on my gmc i have 2 knock sensors and im not possitive if you have two or not under your intake mani but when i replaced both mine i got the same code of low input so i took the small needle out and wire brushed it clean and also traced and ran a new wire just to be safe and that solved my problem. as for bank 1,2 if it helps any my bank one is located engine side driverside and bank2 is engine side passenger side and 3 and 4 are underneath bed side. but you can see the sensors if you look real close near the headers. hope this helps
Posted on Jul 02, 2009
There is an updated resistor/connector package. Very expensive from GM, try your local NAPA or other parts supplier for a replacement
Posted on Jul 09, 2009
Yes u do....I have an 03 sierra and apparently they changed everything in 03.....the harness is over $100.....but u need it....and they dont sell a reg wiring kit from 03 and up....if it was an 02, then yes u could get away cheap......it has to do with the steering wheel switches
Posted on Jan 24, 2010
look for a serious exhaust or intake leak. look for bad wires to the o2 sensor or map sensor. just for starters.
Posted on Jul 20, 2010
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