DBW P2135 intermittent

[homedawg247]

Hey everyone!
-2006 LQ4 6.0 DBW, Manual trans, no VSS hooked up
Engine, Pedal, TAC, TB and Wiring all from same donor vehicle.
Finally able to drive, but getting an intermittent P2135 (A/B voltage correlation error)
When this happens the pedal goes dead (I know this is by design), and the idle sits a touch high (~1400 rpm).
Once I clear the code the pedal works again, and the idle comes back to the base setpoint (675 rpm at operating temp).
I see in the log where there are some weird flat spots in the O2's when the pedal dies.

Problem is, I can't figure out why it's not consistent... If I stay at zero throttle it won't throw the code, if I stay above say 70% throttle and high RPM it won't throw the code...
Is there anything in the tune that could cause this, or is the only possibility a faulty TAC/TB/Pedal?
I've checked the wiring for continuity and ohms and everything has exactly the same resistance... I don't believe it's a wiring issue.
I don't remember having this issue before I cleaned the MAF (yes I used honest to goodness MAF spray cleaner). I let everything dry before I put it back together and fired it up.

Do I need to check the TPS? Can I relearn the TPS? Should I pull the TB and clean the crap out of it?

PedalProblems.hpl
6.0_Working_3-14-2024.hpt
P2135_Section.png

[homedawg247]

forgot to mention, I am unhooking the battery every day since I don't trust leaving it hooked up right now. It's stored off site and I cannot keep an eye on it, so I just unhook the battery when I leave.

[edcmat-l1]

PCM came from a different vehicle?

[homedawg247]

Sorry, PCM came from same donor vehicle as well... Everything is a 'matched set'.

I pulled the pedal and the wiring from it to the tac module and am going to see if I get mismatched values on the A and B circuits. Could there be corrosion inside the pedal assembly that would cause the values to be incorrect?

[blindsquirrel]

***removed, user did not find the factory service manual documents helpful

[homedawg247]

Awesome, I'll look at that in just a bit. Thanks so much for the pointers, it's highly possible I turned something on to keep an eye on it.

[homedawg247]

So in all of the DTC's you listed, anything related to throttle or TB are set and have MIL on either the first or second error. When you say attention of one kind or another, does that mean I have incorrect params for them? Like some should be On/Off and they are not?

I did find one broken wire from the TB back to the TAC mod, but I spliced in a new one a while ago and haven't had an issue with it since. I will look tomorrow and pull the wiring diagram and see which one it was. It could be the different sized wire I used is causing more/less resistance and throwing the correlation off... I did have that thought when I spliced it.

Hope to update with more information tomorrow.

[blindsquirrel]

DBW does not use some of those codes you turned on 'just in case' or whatever. And some codes still on are for things I'm pretty sure you no longer have. Compare to a stock 2006 6.0 file... like I did.

[blindsquirrel]

How about we back up a little bit and you tell us what this thing is. I've been assuming it's a swap into an older vehicle. Is that right? Stock harness? 'Thinned' stock harness? Aftermarket harness?

[homedawg247]

Donor was a 2006 2500 HD
Going into a 1980 K10
I'm using a thinned stock harness... I'll try to list everything I remember removing or changing:

Donor was automatic, i'm manual (SM465 - absolutely no sensors or wiring at all) i've removed all PCM pins for anything related to automatic trans from the PCM connectors
Donor was 2wd i'm 4wd, but no sensors or wiring on my transfer case (NP205)
Donor had AC, I have removed the compressor and all PCM pins related to AC
I have all the 'pink' wires that used to go to the connector in the donor fuse box to a custom relay/fuse box that runs the coils, heated 02 sensors (4 wire), MAF, and injectors
Here's the guide I used to thin the stock harness, it's not an exact copy, but it got me close and I pulled the rest that I knew I wouldn't be using.
(LINK)
PinkWires.png

I have removed all torque management as suggested in another post (https://forum.hptuners.com/showthrea...-rev-very-lost)
The electric fans are triggered by the pcm, but all the relays and fuses are in a custom panel
Fuel system (pumps) are completely outside the view of the PCM
I'm using a standalone Oil Pressure sensor so I turned that off (P0522/P0523)

I'll update as I remember more

[homedawg247]

Also, I went full blown "nerd-alert" and pulled my pedal apart and checked everything with a DMM:
All pins read within spec, at 0% throttle and 100% throttle.
I swept the pedal and looked for any drastic jumps in resistance and didn't see any, so I'm leaning towards the pedal and APP sensors are ok

APP2_png.jpg
APP_png.jpg
Readings.png

[blindsquirrel]

P2135 is the TP sensors in the throttle body, not the pedal. TP1 & TP2 are in the TB, APP1 & APP2 are in the pedal.

Conditions for Setting the DTC

The TP sensor 1 to TP sensor 2 correlation error is more than 6 percent for more than 0.14 second.

OR

The PCM detects a short on the TP sensor 1 signal circuit for more than 0.10 second.

[homedawg247]

EDIT:
WAIT! I spliced a single wire from the TB to the TAC.... I bet that's throwing off the resistance. Let me re-do all that wiring and see if that solves this issue.
BrokenWire2.jpgBrokenWire1.jpg


Ahhh, makes sense why all my checks last night seemed ok. So I took the throttle body off and cleaned it yesterday AFTER this issue started. I looked and I don't think I can open up the TB and dig around in there... What might be my next step? I've read that changing the TB for a new one can cause a whole bunch of problems as well. I can head to the junkyard and find one with the same part number, and I remember seeing an article about a relearn procedure.

[blindsquirrel]

You keep saying things that make me question if you read the P2135 diagnostic I posted.

[gtstorey]

You keep saying things that make me question if you read the P2135 diagnostic I posted.

This is the internet. We are supposed to throw out random ideas for people to try until they hit the jackpot.

[homedawg247]

I read both of the attachments you posted... I'm pretty sure that odd-sized wire could be the culprit. So yes, I did read the documents... Specifically this part:
ReplaceWire.png

Enlighten me: Am I mistake about how the DBW safety cutoff works? One sensor starts at 5 volts and goes DOWN as you increase pressure on the pedal. One sensor starts at 0 volts and goes UP as you increase pressure on the pedal. This is supposed to be an almost perfectly inverse relationship between the two to keep the engine from having a runaway condition. If I spliced in a wire of a different size from the TB to the TAC module, this could very well be causing a difference in the amount of those 2 sensor voltages. I am WELL VERSED in electronics and resistance, I'm not questioning the fact that the wire I used might be causing the entire issue.

Here's what I'm referencing about how it works:
P2135_Def.png
P2135_Expected.png

[blindsquirrel]

The actual code in the GM official service manual calls it "DTC P2135 Throttle Position (TP) Sensor 1-2 Correlation". It is nothing to do with the pedal. It is something in the throttle body or throttle body wiring. The size of a wire does not have anything to do with this, unless it is significantly smaller than original. A bigger diameter wire does not increase the voltage in a circuit.

Since you're an electronics expert, what does it look like when you monitor TP1 & TP2 in your oscilloscope?

[blindsquirrel]

Nowhere in the official GM documents does it ever call anything a "fail-safe mode". You are mixing bullshit info together with the official info. Pick one or the other.

[homedawg247]

Never claimed to be an expert... I said well-versed. If I had access to an oscilloscope I wouldn't be on the internet asking random people I don't know to help me
I also never said a larger wire would increase voltage, I don't think anyone on earth believes a larger wire would increase voltage.
Clearly I'm a shade-tree mechanic and don't have access to all the official GM service manuals like you do. I can only assume by your presumed infinite knowledge but overly-vague answers that you only jump on here to smack-talk people like me who are just starting out to stroke your own ego...

If you'd rather not answer such beginner-level questions I think we'd all appreciate you just keeping your mouth shut. This is literally the second thread i've ever posted on here and both have led me nowhere because you've jumped in both times and provided no REAL answers. You just shit talk about how little knowledge everyone else has compared to you, but you either don't know the answer and just want to act like you do, or you do know the answer but are unwilling to help others learn. I really hope you'll think back to when you were just starting out and how confusing some of these concepts can be to someone who's just scratching the surface of PCM programming.

If I can block you from answering or seeing my posts please let me know how to do that so I don't waste any more of your precious time.

[gtstorey]

You do have access to the GM manuals, they are on the ACDELCO TDS website at a somewhat reasonable cost for a 3 day subscription. Just screen shot the sections you need for the diagnostic needed.