Codes 21 and 26....02 sensors were replaced ~30k miles ago....Help

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Dec 2, 2003
Rockville, MD
Any ideas guys? The 2 codes don't seem related at all with the exception of a faulty ECM and that the engine running rich might have fouled the 02 sensors.

BTW, here's what the FSM says for the two codes under "trouble area":

- Heated oxygen sensor circuit
- Heated oxygen sensor

- Engine ground bolt loose
- Open in E1 circuit
- Injector circuit
- Injector
- Fuel line pressure
- ECT sensor
- Compression pressure

Light's been on for a while, but hadn't gotten around to checking it since the truck seems to be running fine.

The exhaust does smell rich and it smells like a two-stroke upon cold startup, but I don't think those two symptoms are related to eachother.
More info:

I reset the computer last night and the check engine came back on instantly. I had to do some other stuff, so I haven't pulled the codes again to see what's up. It's also running like crap after I reset it. Idle is down to 400rpm and throttle response from idle is sluggish.
I wish i could help, not a clue though.
Nothing decent to contribute other than I don't think a bad 02 sensor would cause those symptoms. I would look for a connector come loose or wire short, etc. Go through the troubleshooting procedures in the manual. Ignore 21 and focus on 26.
Its running slugish and low RPM cause after a computer reset the ECM has to reestablish fule perrameters. Just drive it and it will start running/idiling better.
had same issue, there was a leak by the 02 sensor...some how the nuts vibrated loose and allowed a leak which triggered the CEL .....
Thanks for keeping this going.

It is running better now that the computer has had some time to regroup. However the light is still on. Haven't had time to investigate and it's cold as fawk outside right now.

Does anyone think I'm doing any long term damage by driving it the way it is? I figure if it's running rich, it's not the end of the world, just wasting fuel, but if it were lean, that would be bad.

BTW, would running rich lead to pinging? 'cause this damn truck always wants to ping, regardless of octane used or fuel treatments. It only does it under hard acceleration though around 3k rpms.


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