My aunt has a 98 blazer with the 4.3 and about 130,000 miles. The catalytic converter was changed about 3 years ago and I have replaced all three O2 sensors with new Delphi sensors. But this code is persistent. The truck runs fine, doesn't idle rough or anything. I am not sure when or if the plugs have ever been changed, but I'm not sure that would cause this anyway. Any ideas?
1998 S-10 Blazer P0420 code
- Thread starter nwjones18
- Start date
- Status
P0420 = Catalytic Efficency below limit - BANK 1
If you have had the catalytic changed and the 02's and a tune-up.
Try checking that you don't have a vacuum leak creating a lean condition in the engine or some other unmetered air leak.
I can't remember if this engine has a MAF or MAP sensor or both but make sure they are up to snuff.
Something isn't right with the fuel mixture and burn happening in the engine.
EGR Valve not working or sticking on a bit?
If you have had the catalytic changed and the 02's and a tune-up.
Try checking that you don't have a vacuum leak creating a lean condition in the engine or some other unmetered air leak.
I can't remember if this engine has a MAF or MAP sensor or both but make sure they are up to snuff.
Something isn't right with the fuel mixture and burn happening in the engine.
EGR Valve not working or sticking on a bit?
Originally Posted By: StevieC
P0420 = Catalytic Efficency below limit - BANK 1
If you have had the catalytic changed and the 02's and a tune-up.
Try checking that you don't have a vacuum leak creating a lean condition in the engine or some other unmetered air leak.
I can't remember if this engine has a MAF or MAP sensor or both but make sure they are up to snuff.
Something isn't right with the fuel mixture and burn happening in the engine.
EGR Valve not working or sticking on a bit?
Sounds right to me...
P0420 = Catalytic Efficency below limit - BANK 1
If you have had the catalytic changed and the 02's and a tune-up.
Try checking that you don't have a vacuum leak creating a lean condition in the engine or some other unmetered air leak.
I can't remember if this engine has a MAF or MAP sensor or both but make sure they are up to snuff.
Something isn't right with the fuel mixture and burn happening in the engine.
EGR Valve not working or sticking on a bit?
Sounds right to me...
You can get O2 codes even if they are working properly.
Since they have been replaced, and the cat, that strongly suggests other failure. A bad injector, weak compression, or even an ignition misfire is possible now.
Since they have been replaced, and the cat, that strongly suggests other failure
Was the converter changed with the one from Chevy or aftermarket? If it was aftermarket, you are lucky to get 3 years out of it.
When you get P0420/P0430 code, in almost all the cases, it is the converter which is not doing 100% of the job. In some cases, it is the computer which is lot more stringent that it should be in triggering the light and some of them have firmware update.
- Vikas
When you get P0420/P0430 code, in almost all the cases, it is the converter which is not doing 100% of the job. In some cases, it is the computer which is lot more stringent that it should be in triggering the light and some of them have firmware update.
- Vikas
How would a bad converter cause the P0420 code since it is for the pre-cat sensors? I had always assumed that only the sensor after the cat would be affected by it.
ECM is looking to make sure that number of crossings by the post-cat sensors is significantly less than the pre-cat ones. This implies that the converter is able to store the oxygen. A degraded sensor never switches fast, rather it becomes lazy. If front becomes lazy, then in theory computer could miss-interpret because then both pre-cat and post-cat would be switching similarly albeit lot slower. HOWEVER, when the front becomes lazy, the driveability will be affected severely and you will get code for the pre-cat sensor. If you have no other driveability symptoms and if the only code you get is P0420/P0430, then in almost all cases your converter has been degraded enough for the computer to throw the code BUT not enough to really affect your emissions. All the literature over web will give many papers where the actual tail pipe emission and the federal emission tests run on a car with P0420/P0430 came out clean.
- Vikas
- Vikas
Swap the post O2 sensors and clear the code. If it comes back you may have either bad O2 sensors or bad cat.
I had the same problem with my 2004 GMC 4.3l V6 and replacing the post O2 sensor (used a Bosch) took care of the problem. Passed smog this month and I was getting the code here and there (I have a scan gauge so I was clearing it often)
When did you replace the sensors? Changing the factory plugs/wires/dist cap did nothing for me and this error.
Also you should have FOUR sensors. Not 3.
I had the same problem with my 2004 GMC 4.3l V6 and replacing the post O2 sensor (used a Bosch) took care of the problem. Passed smog this month and I was getting the code here and there (I have a scan gauge so I was clearing it often)
When did you replace the sensors? Changing the factory plugs/wires/dist cap did nothing for me and this error.
Also you should have FOUR sensors. Not 3.
- Status
