Replaced Knock Sensors, Same Trouble Code.

[reffixer]

2002 Sierra 2500, 6ltr, Auto, Code 332.

I had both knock sensors replaced yesterday, drove home, and today service light is back on saying rear sensor low voltage. I ohmed both sensors @ 97k each, traced the blue wires out from wiring harness to the PCM, both OK.

NOW WHAT?

Thank You

Reffixer

[snake428]

Where they properly torqued?? If not the can break internally not detectable through a resitance test.

[reffixer]

Where they properly torqued?? If not the can break internally not detectable through a resitance test.

[reffixer]

Yes, I believe they were torqued correctly. I sure hate to do the job over. *My service book does not list any voltage values to check for ref.

What else can I check?

Thanks Dave

Where they properly torqued?? If not the can break internally not detectable through a resitance test.

[reffixer]

My repair manual says the output voltage is AC, but not how much voltage to test for, or at any particular RPM's.

Where do I go from here?

Please advise, and thank you.

db

Yes, I believe they were torqued correctly. I sure hate to do the job over. *My service book does not list any voltage values to check for ref.

What else can I check?

Thanks Dave

Where they properly torqued?? If not the can break internally not detectable through a resitance test.

 

[snake428]

watch for ac voltage to move at all when you tap lightly on the exhaust manifold with a hammer. Now don't beat the crap out of it but tap it pretty good. This is not allways a for sure either many GM service bullitins on this for sensors being broke on install from over torque does not take much to pop one.

[reffixer]

Thanks for the quick reply;

So the sensors are putting out AC voltage at a constant, which lets the timeing advance, and when they sense a knocking (ping) the timeing is retarded as the voltage output swings. Right.

Can this be done with key on, and engine off?

Sounds like this will determine if a re-replacement is going to be next.

Thanks again a bunch

Dave

watch for ac voltage to move at all when you tap lightly on the exhaust manifold with a hammer. Now don't beat the crap out of it but tap it pretty good. This is not allways a for sure either many GM service bullitins on this for sensors being broke on install from over torque does not take much to pop one.

[snake428]

No the are a piezoelectric sensor that actually creates a small amount of ac voltage on vibration. There for with the key off you can measure for ac voltage when tapping the manifold. This is not a fool proof method for sure but if you have no ac spike they are dead for sure. I can not tell you how many of these I replaced right after someone over torqued be very leary of that.

[reffixer]

Well, I did the voltage test eng running, no voltage output from rear sensor. I believe the torque is 15 lbs. Maybe go 12lbs to be careful. What a pain in the wallet this has turned into.Could be worse for sure. New rear sensor, and another gasket set ordered.

Thanks again for your input.

Dave

No the are a piezoelectric sensor that actually creates a small amount of ac voltage on vibration. There for with the key off you can measure for ac voltage when tapping the manifold. This is not a fool proof method for sure but if you have no ac spike they are dead for sure. I can not tell you how many of these I replaced right after someone over torqued be very leary of that.