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Knock sensors...

Discussion in 'General Chevy & GM Tech Questions' started by mvoss2576, Jan 13, 2011.

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  1. mvoss2576

    mvoss2576 Rockstar

    Check engine light came on this morning... took the truck to the High school auto shop and let them look at the codes while I worked on computers at the campus... anyway, I came back to find out that it was the knock sensors. They cleared the codes and told me to see if the CEL comes back on.

    Now.. I went ahead and priced out the parts.. kind of... I dont know if I have 2 wire sensors or 1 wire sensors... and the price difference.. WOW! The 1 wire sensor was like $55, the 2 wire sensor is like $10.

    Any ideas on which ones I have, or how to tell the difference (without taking everything apart)
  2. Big_Ben

    Big_Ben Rockstar 100 Posts

    Had this same code come up this past summer. Cleared the light, and 4 hours later it came on again. Then early the next morning it went out by itself. Chances are you can actually get away with just cleaning the sensors.

    Sorry I can't help you with which type you have. But if you know the location and are willing to take everything apart, I would suggest doing that and use a good sensor cleaner like MAF sensor cleaner or anything else by CRC to see if that solves your problem first. At the same time you will find out what type of sensor you have. I believe the easiest way to tell is at the connector end. If there are two pins that means 2 wire, 1 pin = 1 wire.
  3. mvoss2576

    mvoss2576 Rockstar

    I believe they are under the intake on my truck... the reason the mechanic told me I would have to purchase intake gaskets....
  4. dsfloyd

    dsfloyd Epic Member 5+ Years ROTM Winner Gold Member 1000 Posts

    try calling the parts department at the dealership, they should be able to tell you which one it is, probably based on vin.
  5. KWG08VMI

    KWG08VMI Rockstar 100 Posts

    i had this same problem on my '02. The CEL would come on for a few minutes then go off. Each time it came on it was for longer periods of time though. Granted it was about a month between each time. Now it just stays on. I don't really want to have to take the intake off and deal with that, so I just check the code about once a month to make sure no new codes have come up.
  6. Big_Ben

    Big_Ben Rockstar 100 Posts

    I've heard that on occasion the cause of this can be knocking lifters. The problem is at startup, while the oil pump is building pressure and getting oil up to the top of the engine the lifters knock a bit and can be loud enough to cause the sensor to be tripped. The other possible cause is that ever familiar piston slap many GMs have during warm up. The best thing you can do to avoid this issue from startup is to let it idle for a few minutes (not just the 30 seconds it takes you to put your seat belt on and think about where you're going to go) before leaving your parking spot/driveway.

    This should only be an issue with an oil pump that might be losing it's prime causing the delay before the oil can get to the top of the engine.
  7. mvoss2576

    mvoss2576 Rockstar

    The light was off all afternoon yesterday, when I drove it around. This morning (when it was cold again) it came on about 20 minutes into my drive to work. I always start my truck 5 minutes or so before I leave the house when its cold.
    I am not going to worry about it a lot, maybe Uncle Sam will owe me some money and I can get it fixed...
  8. silveradotrailblazer

    silveradotrailblazer Epic Member 5+ Years ROTM Winner 5000 Posts

    Some guys on this site have had this problem after installing non-A/C Delco spark plugs.
  9. mvoss2576

    mvoss2576 Rockstar

    I haven't changed spark plugs...
  10. Mean_Green_95

    Mean_Green_95 Epic Member 5+ Years 1000 Posts

    The problem is not allowing the truck to warm up or non ac delco plugs. The problem is the 2nd, or farthest back, sensor. Water gets into the sensor recess and causes the sensor to malfunction. The pieces of foam at either end of the intake that are supposed to keep water out from under the intake do not do a good job. GM also didn't silicon the rubber covers that are on top of the sensors, so water can easily get in there. The only way to keep the code from coming back on is to replace the sensors. While your in there replacing the sensors, you're gonna have to replace the intake manifold gaskets. You will also most likely need a new knock sensor harness since they become brittle. Also, since your down there, replace the plenum gasket because that area typically has an oil leak. I'm going to do the knock sensors on my brother's 04 and my 00 probably during spring breal. I'll probably do a write up on it if we need it.

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