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

[trkpony]

Hey all,

I have a 2007 GMC Envoy 4.2L I6. It has about 150k miles on it, I bought it in 2010 with about 35k miles on it, I'm the 2nd owner.

TLDR: P0332 won't go away. I changed sensors and plugs. What's the next step for diagnosis?

Recently replaced all the front end suspension and steering components, and changed the oil.

The vehicle has a leaky valve cover gasket and has had it for a long time, so it has always had a bit of a misfire mostly just noticeable at idle, it hasn't ever effected driving conditions. When I checked in the past, I know there was oil leaking onto the spark plugs.

I got a CEL for code P0332. Which by my search, shows a low input on bank 2 (rear) knock sensor. I turned the key on with engine off, KOEO, and checked the voltage with a meter holding one probe on the negative battery terminal and the other probe on the sensor connector and got a voltage reading of 4.052V. I have read it is supposed to have 5V, so I am not sure if this 4.052V would set off the low input reading for the CEL.

1. Is 4.052V too low for the expected voltage reading on the wiring harness connector?

Since I am getting voltage, and I don't know the answer to the above question, I figured the wiring should be good to the connector, so I went ahead and ordered 2 new AC Delco sensors from RockAuto. I replaced them and torqued them to somewhere around 20ft/lbs (My clicky torque wrench starts at 30ft/lbs and so I used the other manual dial/gauge style torque wrench that I have and tried to get it close/above the 18ft/lbs reading)

Reconnected sensors, reset the CEL with the cheap little reader that I have and drove around. The code came back and is the same, P0332. So then I went and swapped the sensors from the front bank to the rear bank to see if the code would shift from P0332 to a different code for the front bank (P0331?) following a bad sensor after the swap.

I should have tried this swap PRIOR to ordering new knock sensors, but I didn't think about it at the time... anyways, the light still came back on and it is the same P0332. So swapping the sensors didn't shift the code to the front bank, so I assume the sensors are good... I have seen a couple videos on testing the sensors, but I wasn't real confident in my results when I tried to test the sensor by itself. All the videos show a slightly different style sensor, like from the v8 motor and I wasn't sure where to test on the 4.2L sensor.

So THEN, I replaced the spark plugs with new plugs. 41-103 AC Delco plugs. When I pulled the old plugs there were a couple that shows oil all the way down their threads. But I haven't ever received a misfire CEL. Also, the cylinder 3 plug had cracked porcelain. I'm not sure how that would happen?

Pictures of spark plugs attached.

I haven't heard any weird popping or pinging noises that I would think I should hear if I have uncontrolled detonation.

What's the best next step for diagnosis? obviously I need to change out valve cover gasket, but should I run a wire from a pin to the knock sensor connector if the 4.052V isn't good enough? How would I do that?

thanks for reading all this and any help

 

[Mooseman]

The oil on the plugs are likely leaking plug well to valve cover gaskets.

Check the block's ground connections for corrosion or poor contact. Remove and clean thoroughly.

Then, get the schematic of the circuit from the manual from either Charm or Lemon and check for proper continuity, no shorts to ground or voltage. Check the connectors for corrosion at both ends. With both the sensor and PCM unplugged, there should be no voltage or short to ground.

Checking a little further, according to this video, there should be very little voltage to the sensors. Not the same vehicle or engine but his diagnostic process is very thorough.

So I'd compare the voltage between the two sensors. If just the one has voltage, this would need to be investigated further. In that case, I would look for damage in the wiring harness for a short to another wire.

 

[mrrsm]

I'm just going to copy-paste the "Intro" from a similar post which explains that by using my Snap-On Vantage Pro Diagnostic Scope that includes "Guided Component Tests"... these 60 images of ALL the Steps involved when doing the KS Diagnostics might "Lift The Stone" off of your chest. These are always technical, non-trivial diagnostics, but without you owning your own unit...THIS procedure is the Next Best Thing for what you need to know:

Welcome to GMT Nation,

Let me know if this appeals to you, but I can plug your 2007 GMC Envoy parameters either into my Snap-On Vantage Pro Graphing Multi-Meter and Scope and check out the KS Diagnostics Steps needed here through the "Guided Component Diagnostics" for your particular SUV and then produce all of the necessary Step By Steps that can be Screen Printed and Posted right back here.... if you think that would help.

Usually, all of these Steps are done with exquisite detail (sort of like Holding The Pro Mechanics Hand) and I have to take a digital picture of what each one looks like on the Scanner screen and then crop, scale and edit them one by one (NEVER a Problem with doing that Task) ...so there are always quite a few images to follow on with... but they will all appear here in groups of 20 images at a time as consecutive Posts that you can then download, save and just use them.

With these images, it will be as though these Snap-On devices were in your own hands while you are standing near the truck, trying to figure out WTF to do next. Other Members will probably chime in with much more direct ideas... but from a purely professional point of view...THESE Machines are very hard to beat for showing What to DO, WHERE to DO it and How to DO it with the RIGHT Diagnostic Tools to use... so they do work very well, too.

The First Batch of 20 of 60 Images Follow On:

 

[mrrsm]

Second Batch of 20 Images of 60 Total Images:

 

[mrrsm]

Last 20 Images of 60 Total Images:



End for all Three Posts.

NOTE: Because the Knock Sensor is classified as a "Piezo-Electric" Device that converts the tympanic engine vibrations and untoward shudders from a flexing speaker-cone like set of motions into Electrical Signals that require an Oscilloscope to be able to sense in very fine details and likewise see the images being created during the Tests above to prove that a New KS is working and that other issues (Broken Wiring) are not involved, feel free to drop in on THIS Link and find out whether or not you would like to get an inexpensive one for this problem and not go broke when doing so:

Thread 'How To Use PICO #2204A & HANTEK #1008C Oscilloscopes'

Oct 20, 2019

You don't need a Huge Bag of Coins in order to obtain and use an Oscilloscope for performing In-Depth Wave Form Analysis in Automotive Applications on everything from Problematic Electronic Fuel Injection to obtaining accurate Compression Tests to Diagnose Internal Engine Conditions.

HANTEK makes (...and Amazon, eBay and OTHER Outlets sells) ALL of the discreet equipment components necessary to accurately conduct these types of Automotive Diagnostics ... and all can obtained on a Very Modest Budget.

The Basic Oscilloscope Hardware is listed below:

(1) Windows or surprisingly... a...

• mrrsm
• Replies: 113
• Forum: Technical Discussion

• 

 

[budwich]

The SM "suggests" a "simple" impedance test of the wiring. Basically, disconnect the sensor. With an ohm meter, measure at the connector, each pin back to a known good ground. The reading should be "OL" (ie. infinity... no continuity)... do the measurement with "key off".

Compare the results for each pin and each sensor. Go from the results.

 

[trkpony]

Ok, thanks to you three for the response.
I wanted to give an update because I haven't really had much time to jack with this over the past week.
I watched the video and looked at all the pictures here.
I then disconnected the newly installed sensors and used the multimeter on the ohm setting and checked the sensors.

I can't seem to get any reading on my multimeter from the sensors...

I put it in ohms mode, and selected the auto setting. When the probes are separate, I get OL on the meter. When I put the probes together I get a sound/tone and the meter shows zero 0.00.

I tried to test with both battery cables still connected, and key off engine off. I did not insert the key at all.

There are multiple ground connections on the drivers side of the motor. I tried to hold the black probe directly on the end of the wire spade connectors going to the bolts and also directly on the bolts. Then, I also tried using an alligator clip to connect one black probe to a ground bolt and then each time I tried a different ground bolt. I also held the probe directly on the engine block.

For each ground bolt, I held the other red probe on one pin of the knock sensor to test each pin on the knock sensor... But I'm not getting a reading. I just get OL on the meter. I did this for multiple ground bolts and all 4 pins, 2 on each front and rear knock sensor.
(What are the chances that none of these are good grounds?)

I also did this on the connector and same thing, I get OL. I put the red probe in each of the two pins on the connector separately and held the black probe on the ground bolt and got OL. (I think this is the simple impedance test mentioned above by budwich)

If I grab the end of the red probe I get some readings, I guess it is measuring resistance through my fingers to some other ground location. But I get nothing from the wiring harness connector or the knock sensor pins.

I also tried changing the settings with the auto button on my multimeter, but it doesn't effect the readings. I can change between AUTO, Mohms, Kohm, and just ohm scales.

What am I doing wrong here? Should I disconnect the battery? Should I be connecting both pins on the sensors instead of just 1 at a time?
Do the 4.2L I6 two wire knock sensors work differently than others?

 

[budwich]

I also did this on the connector and same thing, I get OL. I put the red probe in each of the two pins on the connector separately and held the black probe on the ground bolt and got OL. (I think this is the simple impedance test mentioned above by budwich)

Yes... that is the "simple test".... its basically used to "thumb check" the system side of things.... looking for some sort of "draw" (less then infinite). Of course, the results don't take into account a broken wire... but I think you did some other tests (voltage measurements) to prove that part.... BUT I see further down in the SM that ~4.2v (to ground) on each sensor is "nominal".... so it appears your earlier voltage measurement might be low... was that measured on both sensors? I guess that should have questioned at the start....

 

[Mooseman]

Be sure to check your main ground wire from the battery to the block. When I had my engine mounts changed, when they jacked the engine, the main ground wire was basically just green pus and whatever strands of copper that were left just broke. Do a resistance check between the block and the negative battery post. It should be very low, close to 0.

At this point, if I were you, I'd be checking continuity from the sensor connector to the PCM. The diagnostic aid from the manual also says to check the sensor pins to ground. Should be OL.

P0332 — 2007 Chevrolet TrailBlazer 4WD L6-4.2L Service Manual ~ LEMON Manuals

Repair manual for the 2007 Chevrolet TrailBlazer 4WD L6-4.2L, including electrical diagrams, bolt torques, and labor times.

lemon-manuals.la

 

[trkpony]

Yes... that is the "simple test".... its basically used to "thumb check" the system side of things.... looking for some sort of "draw" (less then infinite). Of course, the results don't take into account a broken wire... but I think you did some other tests (voltage measurements) to prove that part.... BUT I see further down in the SM that ~4.2v (to ground) on each sensor is "nominal".... so it appears your earlier voltage measurement might be low... was that measured on both sensors? I guess that should have questioned at the start....

I just checked both the front sensor and the rear sensor. I turned the key on engine off KOEO, then put meter in DC volts mode, then I put the black probe on the negative battery terminal and red male probe on each of the terminals of the harness side connector, I got readings of around 4.02v, to 4.07v. I then moved the black probe to one of the ground bolts on the engine and same readings. I checked both front and back sensor connectors this time and both gave the same readings, so that isn't different from each sensor either.

 

[trkpony]

Be sure to check your main ground wire from the battery to the block. When I had my engine mounts changed, when they jacked the engine, the main ground wire was basically just green pus and whatever strands of copper that were left just broke. Do a resistance check between the block and the negative battery post. It should be very low, close to 0.

At this point, if I were you, I'd be checking continuity from the sensor connector to the PCM. The diagnostic aid from the manual also says to check the sensor pins to ground. Should be OL.

P0332 — 2007 Chevrolet TrailBlazer 4WD L6-4.2L Service Manual ~ LEMON Manuals

Repair manual for the 2007 Chevrolet TrailBlazer 4WD L6-4.2L, including electrical diagrams, bolt torques, and labor times.

lemon-manuals.la

thank you for the direct link to the Lemon manual, I see why you said to check it in your first post, walks you through each step pretty clearly.
So Step 1/2 is check for engine noise or diagnostic proceedure. I know my valve cover gasket leaks oil on the plugs, which is causing a misfire and could ultimately be causing this knocking too, so I need to fix that. But I don't hear any noise so I'm skipping this step for now.
Step 3, as you mentioned is checking the sensor pin to ground, which is what I did above and its reading OL. which appears to be good, I thought I was doing something wrong getting the OL reading.

I'll go try the next steps and report back. thanks again.

 

[budwich]

I just checked both the front sensor and the rear sensor. I turned the key on engine off KOEO, then put meter in DC volts mode, then I put the black probe on the negative battery terminal and red male probe on each of the terminals of the harness side connector, I got readings of around 4.02v, to 4.07v. I then moved the black probe to one of the ground bolts on the engine and same readings. I checked both front and back sensor connectors this time and both gave the same readings, so that isn't different from each sensor either.

Now you getting into the "dirt".... both readings are "too conveniently low".... yet only one "complains". Its quite possible that your meter / leads might be "uncalibrated" such that a "small error" results (ie. the measure is actually close enough to the expected 4.2v.). Note: this value does not actually provide any direct contribution to the resulting code although perhaps if it was significantly low such 2-3v then maybe. The code appears to be set from more of a "ac signal RMS" type value. Hence, the sensor vibration frequency AND amplitude are important.

ADDED: did you measure the voltage on BOTH pins at the connector? OOPS.... I misread the SM... the 4.2v is the upper limit. The voltage reading should be below that value... which yours are.


At this point, without getting some sort of signal scope, it might be tough to find the issue... perhaps pointing to the PCM. Bringing you to the PCM... have you pulled the connector and looked at the condition of the pins in the connectors.... focusing on those associated with the sensors? Its possible that the have oxidized enough to cause a "base voltage issue" (ie. slightly lower sensor "bias").

NOTE: probing any pins in a connector is dangerous to the pin itself IF you don't use the appropriate size probe. Too large a probe may cause damage such that the connections thereafter are NOT very good in future operation.

ADDED: another test suggested in the SM is a "active test". disconnect the sensor in question. Carefully connect your meter with the sensor wire (ie. rig up some form of "T"). Set the meter on ac volts. Set the key ON ENG OFF. Get a reading... probably nothing... wait for it settle. Then get a non-metal "striker" and tap on the engine block near the area of the sensor. Monitor the meter, you should see some change in voltage showing up as the sensor "causes AC" to occur (basically modulating the dc signal... that 4.2v DC... I think).