Crank sensor/throttle pedal position codes

[JPaul]

So the last couple of months or so I have intermittently and randomly been getting P0335 (crank position sensor signal) while driving. It will happen once maybe every week or two. I'll just be driving along and suddenly it will come up. My Ultragauge will show zero RPM (the dash will still show RPM's though, presumably it's using the camshaft sensor for that data). Still runs and drives but shifting is a bit harder due to a form of limp I'm assuming the PCM is doing. Turn the car off, turn it back on and it is fine and no issues for at least another week or two, then it will do it again.

Several months prior I was having issues with the throttle pedal position signal, but at the time I got it to go away by pulling the connector at the pedal and shooting it up with DeOxit. That is until today. I went to start the truck and after it started the CEL came one and reduced power message was displayed. Checked the codes and this time I got both the crank signal code and the throttle pedal signal code (P2127 I think it was). Shut it off, started it back up and after a long crank it started up. Still had the crank signal code but throttle pedal code was not active.

Normally one time of and on is enough to make it happy, but this time I had to drive a couple short stretches and shut off/start the truck before I finally got it happy. The last time before it stopped complaining I checked over all the connections I could. Battery terminals were solid and looked OK, didn't notice any obvious chafing anywhere, wiggled the wires to the crank sensor as well as I could reach them. Started it up after clearing the codes and disconnecting the Ultragauge and it was fine.

The crank sensor was a brand new AC Delco part, when I rebuilt the engine last year I used all new sensors to avoid any of them dying on me. From what I can remember when I put the wiring harness back in place I did not notice any damage to the connectors, sheathing, wrap, or insulation.

I have a feeling based on the very random incidents and length of time between them that it probably is not the sensor nor the PCM but more likely a bad connector or damaged wiring. Unfortunately the crank sensor is behind the starter so I have to pull that off to get to the connector to check it and the wiring. I have also noticed that sometimes the engine takes a bit longer to start than other times and I am wondering if it is due to the signal from the crank sensor not working right or being interrupted for a moment when trying to start the engine, but then recovers and the PCM is OK with it.

Any other thoughts or experience with this? I still have the stock battery terminals but have a pair of military style clamps I have been meaning to put on. I know the battery terminals can cause weird issues when they start to go, so I will be trying to work on that this week.

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[Guerrero]

I cant help with that particular issue....i think that I would try to replace the pedal assembly (with the sensor included) and replace again the crank position sensor...and then, see how it works, if its the issue reapeared then check wires and connectors.

For you about help with the wire and connector of the crank position sensor, you have to know that you can access it through the driver side fender well, you only have to remove the plastic of the fender well and you will have direct access to crank possition sensor and wires...hope this help you out!

Guerrero

 

[amrg]

Does your truck start from the first time?
The crank sensor is needed for starting the vehicle. If faulty, the engine was take 2 tries to start as the pcm wouldnt know which position the cam sensor is at (on the v8 the cam rotates twice for every single crank rotation)

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[JPaul]

Does your truck start from the first time?
The crank sensor is needed for starting the vehicle. If faulty, the engine was take 2 tries to start as the pcm wouldnt know which position the cam sensor is at (on the v8 the cam rotates twice for every single crank rotation)

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It always starts the first time no matter what, though I think I recall that this last time when I first tried to restart it after the initial start it just cranked for a while before I stopped, when I tried it again it started up. Sometimes it takes a half second or so longer than normal to start, but it will still fire up with the first key turn. I've noticed that when it takes longer to crank I can actually release the key and the PCM will keep cranking the engine until it starts, but that usually doesn't more than a second or so. It seems like it just isn't always getting a signal. It could just be dirty contacts or something. It sucks trying to work on it because the exhaust is right there as well so you have to wait for everything to cool down, which by the time I get home from work means waiting until it's dark and cold to work on it. My garage is still full of crap though I am slowly getting it cleaned out as I bring stuff up to the new area we will be moving to this summer.

 

[JPaul]

Acted up again today. Went to start the truck to head home after work and the check engine light came on along with Reduced Power and traction control or stability system disabled. This time though the code thrown was P2122, which is a low signal voltage for the throttle body. No other codes were thrown. So that is three completely unrelated codes now. The throttle body and the crankshaft sensor share the same connector to the ECU, but the pedal is on a different connector. They do all utilize the 5v and low signal lines on the ECU, and with this last code talking about the signal voltage being too low, I'm concerned that the 5v lines are having voltage supply issues.

I eventually got it to start up correctly and made it home Ok with no more issues. Went to dinner, no problems. Came home from dinner, no problems. So I spent the time tonight replacing the battery terminals with the pair of military style terminals I've had sitting around for a while. I did not crimp on new cable ends and instead cut down the existing ones, pressed out the extra stud in them and enlarged the hole the stud was in to fit the 3/8 bolts on the terminals. I've been meaning to put them on so that I can finish installing my rear power center, but winter and work and everything else has gotten in the way. Nothing like being forced to do a project you've been putting off for months.

I also fixed up the mounting for the battery since the first time I modified it for the group 31 I did a garbage job and it was sliding all around in the clamp and tray. Now it is rock solid and should not go anywhere. Still not pretty and needs to be redone properly when I have the time, but it will do for now.

Lastly I disconnected the three connectors to the ECU and reseated them in case something was wonky after rebuilding the engine last year. Seems unlikely to help, but occasionally with servers at work we have to reseat riser cards and RAID controllers and memory modules if they start acting up, so it certainly is possible to be a fix.


I really hope that replacing the terminals will help. If it continues to act up I'll crimp on new cable ends and give that a go. If that still doesn't work then either there is a bad ground somewhere that is screwing with the computer (so far they all look ok, no corrosion or loose connections that I have found so far), or there is damage inside the wiring harness (possible but seems unlikely), or there is something wrong internally with the ECU. At least it is becoming more frequent so that I can have an easier time trying to track this down. The whole once every couple weeks thing was annoying and made troubleshooting and testing fixes time consuming.

I just hope it isn't the ECU, I'd rather not have to mess around with replacing it, but if I do then I'll probably go ahead and get a tune from PCM of NC or someone. Though replacing the ECU would be less painful than tracing down a problem inside the wiring harness...

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[Mr_Rich]

Did you ever replace the throttle body? The TPS sensor is integral to the throttle body. I never had any TPS issues with my other vehicles that are drive-by-cable vs. DBW like my 3T. When it acted up on mine it behaved with similar weirdness. I'd hook up my scanner to my 3T with key on/ engine off and press on the gas pedal and observe the TPS values increment and log them as kind of a base value to gauge later on.

 

[JPaul]

Did some more digging this morning, one source mentioned that the throttle pedal code can be caused by water getting into the connector at the BCM, so I pulled the trim panels off and checked them out. The two for the BCM itself looked fine, but the third one next to the BCM had some green copper corrosion reside on it. Not a lot, but enough to be obvious. I sprayed all three with De-Oxit and plugged them back in, reinserting the one with the corrosion stains several times to make sure the contacts were clean. That connector is for the instrument panel harness to the body harness, and the body harness goes into the engine bay and connects to the ECU.

I also found some recalls for the HHR that describe issues with those same codes popping up randomly and the two recalls regarding that indicated it was an issue with the engine harness rubbing through in a couple locations. I've looked over the harness and am not seeing anything like that, but it apparently is a very real possibility if this continues to be an issue.

 

[JPaul]

Did you ever replace the throttle body? The TPS sensor is integral to the throttle body. I never had any TPS issues with my other vehicles that are drive-by-cable vs. DBW like my 3T. When it acted up on mine it behaved with similar weirdness. I'd hook up my scanner to my 3T with key on/ engine off and press on the gas pedal and observe the TPS values increment and log them as kind of a base value to gauge later on.

I have not replaced the throttle body. So when you're acted up it threw random codes? If it was just the accelerator pedal and the TPS then I'd think that was the problem, but the crankshaft sensor as well? It could be related if the TPS has an intermittent short to ground in it. I'll check it out. It was the one sensor on the engine I did not replace when I did the rebuild.

The TPS on the V8 is not integral, so I can replace just the sensor portion of it. It clips on with metal clips. I did take it off and cleaned it when I had everything apart, but I didn't realize at the time that it was sold separate from the throttle body.

 

[Mr_Rich]

I have not replaced the throttle body. So when you're acted up it threw random codes? If it was just the accelerator pedal and the TPS then I'd think that was the problem, but the crankshaft sensor as well? It could be related if the TPS has an intermittent short to ground in it. I'll check it out. It was the one sensor on the engine I did not replace when I did the rebuild.

The TPS on the V8 is not integral, so I can replace just the sensor portion of it. It clips on with metal clips. I did take it off and cleaned it when I had everything apart, but I didn't realize at the time that it was sold separate from the throttle body.

If you replace the TPS sensor you're golden, I bet. I prefer my vehicles that are drive by cable vs. DBW like the GenIV GM engines. They just seem to be more dependable to me. If that TPS sensor is separate on the Alpha that is a savings right there by avoiding the cost of the entire assembly.

I've been cleaning up my office in prep for a move and coming across all kind of surprises; like a letter GM sent in 2015 regarding replacement of throttle bodies on Hummer H3/ H3T's. It just said on some models in year 2009 there might be a problem and it was an offer of reimbursement. It's like that darn ignition switch problem that activates PassLock. Such a simple little piece that keeps the truck from starting for 10 min.

 

[JPaul]

Well, it's not the TPS sensor. The last several times the issue has come up it has consistently been P2122 (TPS low signal) so I went ahead and installed the new one that I had ordered on Monday. Yesterday, no problems. This morning went to leave for work and didn't even get a quarter mile from my house and the P2122 came up again. So, yeah.

Before I put the new TPS in I checked the wiring but didn't find any problems. 5v signal was fine, no excessive current flow through it (checked with a milliamp sensitive DC clamp meter), and wiggling around the harness from the ECU to the engine produced no issues.

It's so random and still is about a week in between incidents, so this is driving me nuts. I know the pedal was replaced at one point by Superbuick, and it is a GM part as well so I doubt there is an issue there.

You'd think that if this was a wiring issue I'd see it more frequently since the roads I drive on for my commute are far from smooth. I'm running out of ideas to try before I start tearing apart the wiring looms to loom for internal shorts, or just replacing the ECU.

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[JPaul]

Ok, I'm seeing conflicting information, is P2122 TPS low signal or APP low signal??

 

[JPaul]

So I looked back at Superbuick's build log for this rig and he replaced the Throttle body and pedal back in 2013, about 5 years ago, which was about 5 years after the truck was built. So maybe it is the accelerator pedal and they only get about 5 years out of them before they start going bad? Wouldn't really surprise me with how much they get used. I think this is the first drive by wire vehicle I have had.

 

[amrg]

Try replacing the throttle body. Not cheap. If you have access to another GM truck that you can borrow its throttle body for a day it could help!

Im fighting a P2135, replaced tps, pedal assembly (my throttle body is fairly new) and checked the wiring and sprayed em with contact cleaner. Now in waiting...

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[JPaul]

Try replacing the throttle body. Not cheap. If you have access to another GM truck that you can borrow its throttle body for a day it could help!

Im fighting a P2135, replaced tps, pedal assembly (my throttle body is fairly new) and checked the wiring and sprayed em with contact cleaner. Now in waiting...

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Why would I need to replace the throttle body itself if I just replaced the Throttle Position Sensor? Are you thinking it's an issue with the motor?

And I would need to borrow one for at least a week before the code rears its head again, this isn't a constant fault, it happens once a week or so, and that is with driving it every day.

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[amrg]

Have you checked the pins at the pcm? Sometimes they get corroded. Check the wiring for continuity too

As for the motor, Why not? I may have not read entirely your thread but from what I did read you are running out of things to check!
Its an ass to change and not be the culprit but if you can get a loaner why not! The GM service manual eventually tells you to replace it then the pcm once you've done everything else!



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[JPaul]

The pins at the PCM are fine, I pulled all the connectors off a couple weeks ago to check them and saw no issues. I haven't checked the wires completely, so there is still that. Superbuick did replace the whole TB 5 years ago on this, so it's not totally old, not that it means that I don't need to replace it. I know last year I was getting different codes for a bit but the same symptoms and it was pointing to the pedal assembly, so back then I pulled the connector off and sprayed it with De-Oxit (really good, but really expensive contact cleaner, I also used it on all the connectors to the ECU and engine sensors/components when I rebuilt the engine last year) and shot it up and put the connector back on and stopped having issues until recently.

If the P2122 is related to the pedal then it might just be that it's finally going out. Obviously it's not the TPS since I replaced that but I still get P2122, so I think that code is either for either one or it's for the pedal. I have a new pedal coming today because I'm running out of ideas and it is so bloody intermittent, and I've had problems with the pedal in the past. I've inspected the wiring harnesses as much as I have been able to so far and am not finding any pinch points or chafing, but I'm having a heck of a time trying to figure out where exactly the wires for the pedal run, I'm not sure if they go into the engine bay from the driver or passenger side.

I really need to get a real FSM, the PDF's Schwarttzy has up don't seem to be complete, there's no pages showing all the connectors and their pinouts like I've seen in FSM's in the past. And the wiring schematics leave much to be desired since they rarely show any connectors in between components (like if there is a connector the wires pass through when going from the dash harness to the body harness).

 

[Mr_Rich]

It's kind of a long shot but I have another idea. In my electronics and auto career I've seen where individual terminals in a gang plug don't seat all the way. I've used duck bill pliers (no crosshatch teeth, just flat surface) to grab the individual wires and try to make sure they are secured in the gang plug. Sometimes it looks like one wire is sticking out a bit further than other ones. I think you covered any other issues with the contact cleaner.

 

[Mr_Rich]

Oh yeah, and the FSMs you talk about for H3s are three manuals that stack about ten inches high and are expensive.

 

[Traxx]

The oem manuals are a bit pricey but they pay for themselves in short order unless you have a mechanic that does all your work.

 

[JPaul]

Yeah, only thing I won't touch is an automatic transmission. Aside from the transfer case and differentials, I've worked on virtually everything on a car before. This was my 4th or 5th engine rebuild. The PDF's schwaarttzy has got me through that bit fine, and the schematics are helpful, but when it comes down to trying to troubleshoot fiddly things like this is when you wish you had the official FSM.