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Ruh Roh...

Discussion in '1992-Present Chevy & GMC models' started by willyswanter, Nov 18, 2002.

  1. willyswanter

    willyswanter 1/2 ton status GMOTM Winner

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    Ok, history first...

    About 5 weeks ago I got a constant SES light. So I went to school and scanned it with a SnapOn scanner and it showed a heater circuit error on the bank 2 pre-cat o2 sensor. It was throwing my fuel trim way off for that side, basically dumping fuel in. So it was running a little rough but power felt the same. Yesterday I had my battery disconnected because I was welding on the frame and that reset the SES light, so it was off.

    Ok, now this morning I left here to go to class and I started it up, started fine, and I headed off... The SES light was still off. I got about 3 minutes from my house and came to a stop sign. I stopped, then when I left the sign I got a flashing SES light on/off for 30 seconds accompanied by the computer not letting my engine run over 2000 rpm. This all lasted for about 30 seconds then the light went solid and driving returned to normal. Then, later this afternoon as I was driving home, the light went off. But a bit later it did the same 2k rpm thing but no flashing SES light, it actually never came back on.

    So, during class I asked my instructor about this and he said it was the computer giving a warning that the sensor had completely failed. So, on the way home I picked up 2 brand new sensors for 89 bucks each /forums/images/graemlins/mad.gif. I installed them, but have not had a chance to drive it yet since my truck is currently blocked in by about 7 other cars.

    Ok, question is, is what my instructor said true? I didn't get a chance to run the computer again on the scanner but I will tomorrow and see if there are any other codes stored now. But do you think this 2k rpm limit thing and all was due to the o2 sensors? I also have been experiencing a rough idle for about 3 weeks or so and it was still there when I started the truck after putting the sensors in, although the truck was cold and probably hadn't even gotten into closed loop yet since I only started it and ran it for maybe 1 minute.

    So, since the truck has 150k, I plan on replacing the never been touched factory wires and plugs and maybe cap and rotor. Anyway, I'm not to worried about this, main question is about the 2k rpm limit thing... Any ideas? Anything else that would cause that?
     
  2. ntaj*ep

    ntaj*ep 1/2 ton status

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    The check engine lamp will come on and stay on if theres a hard fault detected in any sensor curcuit. A flashing check engine lamp indicates there is a runnability issue with the engine (sensed be several sensors)and if persists will damage parts. The engine if run with the flashing lamp will then go into a "open loop" type condition, otherwise know as "limp home mode" to try and save that from happening. The miss that you describe if severe enough will damage, among other things the Cats.
    Your heater cir. fault tells me that the sensor is indeed faulty. If it were a straight up o2 failure code I would tell you the miss may be the issue and the o2 secondary to that. The flashing lamp I doubt has anything to do with a o2 code. Tell us what you find on the scanner tomorrow /forums/images/graemlins/thumb.gif
     
  3. willyswanter

    willyswanter 1/2 ton status GMOTM Winner

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    Will do, but one last question... If the flashing light thing only lasted for 30 seconds, what does that mean? I mean if something else electrical fried on the engine it wouldn't just last 30 seconds...
     

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