Knock Sensor Bad?

Discussion in 'GM Powertrain' started by silveradokid, Dec 24, 2009.

  1. silveradokid

    silveradokid New Member

    I have a 99 silverado and the check engine light came on and I ran a diagnostic test,these things came up, Knock sensor low input, and the 2 oxygen sensors or the passenger side were bad. So i replaced the two oxygen sensors, and cleared the dtc's, in hope that they would fix my knock sensor problem. I could here the pistons knocking before i replaced the o2 sensors, I've driven about 30 miles and the truck seems to drive better, but the knocking came back so i ran another diagnostic test, and the knock sensor problem has come back up. From my understanding, in order to replace the knock sensors you have to take the intake manifold completely off, am i right? And is that a hard job? If i need to do that i was thinking i probably should replace anything that's in there just because i have the intake manifold off and nothing has been replaced in there, so if anyone knows any information on this stuff it would be very helpful. My truck is a 1500, and has 150k miles on it. Thanks!
  2. weekend wrench

    weekend wrench New Member

    I replaced my knock sensors - 2002, 5.3L, 2wd, 185K. It was my first "serious" venture into the engine, but I followed the Haynes book instructions...and it worked! Lot's of disconnects but very doable. When doing the job, replace both sensors (appx. $35 ea) and the wiring harness. Also, I replaced the manifold gasket and bolts. The tension is in inch pounds for the bolts (spec in the Haynes book). As it was my first job beyond brakes and shocks, fluids, I broke off a bolt because I was not intelligent enough to note the inch pounds spec... last recommendation, use a paint marker (Markal VAPM - to mark both ends of the hoses and electrical connections when you take things apart to make it easy to know what goes where when you put it back together.

    Good luck,

    Weedend Wrench
  3. weekend wrench

    weekend wrench New Member

    Oh yea, I also searched all the threads on this forum with the key words, Knock Sensors, and read up on ideas, etc. There's one thread that has step by step photos with instructions. Very good.
  4. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    If your engine is still knocking the knock sensors may still be working but unable to stop the knock. Are you using a good brand of fuel? Did you try a tank of premium to see if it makes a difference? You can watch the knock sensor feedback on a scan tool and verify if the sensors are working or not before you tear into it.
  5. earlytimz

    earlytimz New Member

    Will a bad knock sensor always throw a trouble code? I've been dealing with knock for a while now, but always assumed it was due to the hypertech programmer I put in a few years ago. It didn't start doing it at first, but for the last 1.5 years or so, I've had to run a minimum of 89 octane to keep the knock in check. Even with that, I still get a little knock every now and then. Running 93 octane eliminates it, but also eliminates my wallet. I have the hypertech set for 87 octane too.

    Any ideas? I've never had a knock sensor code come up, so I'm wondering if they will always trip one.

    99 silverado, 4.8, 4x4, K&N filter, Hypertech programmer, 160* thermostat, MAF screen delete, 190k & counting...


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