Knock Sensors

[mirvingm]

I'm having chronic troubles with knock sensors on my 2001 GMC 2500HD 6.0L.

I've replaced them 3 times in about as many months. The first ones were "Lifetime warranty" But they failed twice. I replace both sensors the wiring harness and manifold gasket each time.

The last set was AC Delco and now I'm having to replace them again after getting the knock sensor codes. Any insight to this hit and miss problem?

I replace them and drive 10-14 miles and the codes are back!

One final question? Can I reuse the intake manifold seal if it been installed for a month or less? This goes against my better judgement! But I spending a small fortune on manifold gaskets.

I'm getting efficient at completing this work! But I don't want to be!!! Any help appreciated.

 

[Virtus_Probi]

The signals from the knock sensors need a lot of electronic processing and I wonder if something has failed in that chain instead of the problem being in the sensors themselves.
IIRC, the knock circuits I was familiar with used some RC filtering outside the signal processing IC, so maybe one of those components has failed...or the IC itself has somehow started to fail over time.
This would all be internal to the ECM and probably nearly impossible for a layman to fix, so replacing the module itself would be necessary. Could be an expensive debug step for the OPer, though.

Maybe somebody from the auto repair world might have a different and cheaper suggestion...

 

[TurboTravis]

I am not sure if this will help..

I was getting a knock sensor code on my 2005 Silverado 5.3. It has 2 sensors, just like yours, in the same location. I did not feel like pulling the intake, so I wired one sensor to both wires on the harness (it will make sense if you have seen the harness). Basically, the ECU 'cycles' when it checks the sensors, so it does not know if it is checking the front or back sensor-it is just looking for a good sensor reading. In other words, it does not care if the good reading is from the front or back sensor. With that said, I was able to eliminate my codes by doing this simple work around. I would try wiring to both wires to one sensor if I were you, and then try the other sensor if it does not work initially. You have nothing to lose.

 

[beast3300]

besides using GM sensors did you replace the short KS harness?

 

[mattd]

Were the wiring pigtails replaced? Have you checked for any RF interference?

 

[super20dan]

Originally Posted by TurboTravis
I am not sure if this will help..

I was getting a knock sensor code on my 2005 Silverado 5.3. It has 2 sensors, just like yours, in the same location. I did not feel like pulling the intake, so I wired one sensor to both wires on the harness (it will make sense if you have seen the harness). Basically, the ECU 'cycles' when it checks the sensors, so it does not know if it is checking the front or back sensor-it is just looking for a good sensor reading. In other words, it does not care if the good reading is from the front or back sensor. With that said, I was able to eliminate my codes by doing this simple work around. I would try wiring to both wires to one sensor if I were you, and then try the other sensor if it does not work initially. You have nothing to lose.

brillant

 

[ls1mike]

1. Get your sensors from the dealer. Not AC/Delco from on line.

2. Replace the wiring harness if you have not. That will do it set the code quick.

3. and this is important. They have to be torqued to 15ft/lbs or it can throw a code. Don't just goodandtight them in there. It is one of the few things I torque.

 

[ls1mike]

Also mileage? It might be time for GM top end cleaner...Seafoam. You could be getting detonation from carbon build up.

 

[clinebarger]

Lot's of good responses

You could very well have a wiring issue! This system is pretty straight forward.

*Unplug the Knock Sensor jumper harness, With the key-on engine off, Probe the engine harness side, You should have a 5vdc bias voltage on BOTH knock sensor circuits, It can be slightly lower than 5 volts.....Like 4.95vdc for example.

*Both Knock Sensors should "ohm" at @ 99,000 ohms, Taken at the Knock Sensor jumper side.

*The 99,000 ohm bleed resistor will knock down the 5vdc bias voltage @ 1/10th of a volt or 100mV when reconnected. I recommend "backprobing" at the PCM connecter with a T-pin.

*These 2 circuits are very sensitive....You may want to disconnect both PCM connectors (7mm socket), Blow them out good & reconnect them!!

*More in depth diagnosis will require a scope so you can watch the AC sine wave that rides the 5vdc bias voltage when noise is introduced via knocking on the block.