NEED HELP CEL with P0332 rear knock sensor - how to test wire?

[mr_infamous]

If both sensors are the same part, you could try swapping the front and rear sensor connectors to be absolutely sure it's a problem with the wiring or PCM. With reversed connectors, P0327 should set instead, obviously.


I'm more interested in why none of the online FSMs detail how the knock sensor signal is interpreted. My guess is engine vibrations cause the piezoelectric sensor to generate a voltage and an ADC in the PCM interprets the peak voltage of a spike as the "power" of the vibration (worse knock = higher voltage), meanwhile the CPU keeps track of the spike frequency and P0332/P0327 set whenever the voltage spike goes out of range or when fewer spikes are occuring than expected.


Perhaps there's another GM vehicle that uses the same sensors but has more details on the specifics for what a normal sensor signal is supposed to look like?

 

[trkpony]

lots of "detective work"... have you looked at any of the freeze frame for the code?

Ok, I installed new upstream and downstream o2 sensors, re-ran the logs.

I tried to do the freeze frame of the check engine code within Torque Pro app, but it wont show any info about it. see attached screenshots...

I have also attached the new logs from after installing the new o2 sensors. I don't really see anything wrong. or out of the ordinary.
No misfires recorded.
Long term fuel trim is staying from 0.75 to 7 % positive, varies with rpm and settles back to 0.75% to 3% after driving around, but it isn't crazy high or low to compensate for some air/fuel issue. A quick search says that from -10% to +10% are generally normal and don't indicate any problems.

So I'm back to need to do a top end cylinder cleaning with the berryman intake and valve cleaner but i'm going to do a combustion chamber type soak with it.
and maybe an issue with the computer itself.

 

[trkpony]

If both sensors are the same part, you could try swapping the front and rear sensor connectors to be absolutely sure it's a problem with the wiring or PCM. With reversed connectors, P0327 should set instead, obviously.

I'll see if the connectors will reach. I swapped the sensors themselves, and was going to look at swapping the pins in the PCM side connector to flip the wiring, but I could also do this and swap the connectors if they reach.
I'll check it out and report back.

 

[budwich]

I tried to do the freeze frame of the check engine code within Torque Pro app, but it wont show any info about it.

Not sure but I don't think a "pending fault" will cause a freeze frame snap shot since the fault hasn't actually occurred as the conditions for settings the code haven't been met.... my guess / read.

ADDED: thinking about your meter testing some more. How about this impedance test. Disconnect the connector from the back KS. Locate the low reference pin. This low reference is coming from within the PCM. I believe you measured the impedance on the pin to a "known good ground" and got an "open". That's good as that means there is no short to ground. However, it doesn't really tell you if the "low reference" is indeed "low" meaning it isn't some form of "non-zero impedance". So then how about testing from one low ref to another with the chance that perhaps in the PCM, various low ref's come from a common source. As a guess, I would try using the MAP sensor. It too has a low ref. Disconnect the connector therein, and do a resistance measurement from the pin in the map connector to the low ref in the KS connector. Do a second test with the same setup to the other KS (the good one)... which you then compare. Of course, IF the low ref isn't coming from a common circuit in the PCM, it won't help but it doesn't hurt to try. The alternative is "guessing" at finding a low ref at the pcm some where that is common.... but I hate playing with the PCM connectors and pins because you maybe opening up a "can of bad connections" thereafter.