Tuning causing P2138 throttle body code? or cooincidence?

[mach]

a couple weeks ago while tuning, i started hitting full throttle. then received a P2138. basically wires D and E do not match on throttle body. after stabbing the pedal several times, i was able to get it to go full throttle and code never reappeared.truck is never driven at that high of throttle, so i thought maybe a fluke.
Fast forward to now. found the injectors to be leaking at shutoff. swapped in another set(stock) and all was well. except part throttle trims were a hair off now. went and cleaned the maf up and touched up the VE. i was completely done with the ve and truck ran great. turned everything back on as i normally do, flashed it in. fired up and went on drive to check things. made it about 50 ft. and got the P2138 again. except this time ,it comes on within 5 seconds whether i start the truck or not. with zero throttle input. putting prior and original tunes in have made no difference either. havent seen any app1 or app 2 voltages out of whack either ,. did pedal/throttle body take a dump cooincidentally?

[mach]

also at key on, im logging "APP 1-2 corr fault" and it goes from ok to fault within 4 seconds almost every time. my app1 voltage at idle is 1.6-1.8 and app2 is .45. according to what ive found, the app 2 is right on. app 1 should be below 1 volt. hopefully that means the pedal sensor is bad.

[blindsquirrel]

What year/make/model?

[mach]

08 tahoe. finally unhooked battery and replugged in throttle body/pedal. drove fine for 15 minutes. then happened again cruising at 50 mph. reset and drove on. happened again 5 min later when i floored it. i had scanner on when it happened. only thing out of whack i can see at that moment, is that the commanded throttle stays right with the absolute throttle until about 60%. then commanded went to 95 and absolute never increased. thats when it failed . doesnt explain the times at idle though. gonna check wiring for bad connections tomorrow

[blindsquirrel]

P2138 is nothing to do with the throttle body.

If you have 0v for APP1/APP2 with the APP unplugged, and ~5v with APP1/APP2 jumpered to 5vref, and backprobing APP1 shows the same 1.6-1.8v as you see in the scanner, I'd be replacing the APP/pedal assy.

If you can't make the scanner values go near 0v by unplugging and near 5v by jumpering, I'd suspect the ECM.

[mach]

yes. it is a pedal code. for some reason i was connecting throttle body to that somehow being they are related. will check wiring tomorrow first before replacing

[mach]

so, i forgot last night. when i had battery unhooked. it drove fine for awhile. then i flashed a small change i wanted to make. 5 minutes later is when all that happened again. so today, i unhooked the battery , and started again. ive been 50 miles so far, with various driving. not a single issue. seems only time this has ever happened is while actively tuning, or within minutes of a flash. not sure thats a cooincidence just yet.

[mach]

well. over 100 miles of stop and go. off and on driving. not a single issue since unhooking battery.

[blindsquirrel]

So... this is going to sound like me just being an asshole for fun, but it's not.

You mean that after you flash it, APP1 is at the weird code-setting 1.6-1.8v at rest, but disconnecting the battery puts it back down to under 1v where it should be? No other changes? Really?

[mach]

literally did nothing other than reconnected battery. checked again on another run, it was about 1v. not the 1.6 as earlier. no idea really. other than this problem never surfaced until actively tuning/flashing. drove another 50 miles today. no issue again. very odd,but also seems to pattern using hptuners. would be interested to see if anybody else ever ran into this. i never have on any other gm until this one.

[blindsquirrel]

I would be real tempted to set up a DVOM in the cabin in easy view, backprobed into APP1 & GND. It would drive me crazy until I knew for sure if that voltage reading after a flash was real or something weird happening in the ECM.

[mach]

yeah. but ive got enough lost time here and in all the other work i have to chase a dream. lol. my gut says weird ecm crap with flashing. but i know everybody will say thats not possible. anything is possible when monkeying with electronic stuff. ive seen weirder things happen. customer has never had this code. and ive worked on this truck for years as well on other things. engine, trans, etc. never did this occur until tuning needed done. thats the only explanation i can come up with. unless it comes back again.

[cadillactech]

You might have loose fitting terminals on the ECM connector or the APP sensor connector. Common for GM stuff to have intermittent failures.

[blindsquirrel]

Loose/intermittent would cause lower than actual voltage unless it was on the APP loref (not pulling it as low as it should be = higher voltage), but since both APP1 and APP2 share a common loref it would affect both of them at the same time. I'm unaware of a connection issue that could cause higher voltage on only one of the two APP return pins.

[mach]

You might have loose fitting terminals on the ECM connector or the APP sensor connector. Common for GM stuff to have intermittent failures.

anything is possible. its just really odd how it follows a pattern is all.

[cadillactech]

Loose/intermittent would cause lower than actual voltage unless it was on the APP loref (not pulling it as low as it should be = higher voltage), but since both APP1 and APP2 share a common loref it would affect both of them at the same time. I'm unaware of a connection issue that could cause higher voltage on only one of the two APP return pins.

Most GM vehicles with a modern TAC control have an APP assembly has 6 wires and each individual APP sensor has a 5V ref, low ref and a signal wire.
This is the schematic for the 2008 Tahoe TAC and APP circuits.
1906839.png

So if you have high resistance on one of the low ref circuits, your 1-2 correlation will be off. Or high resistance on any of the individual circuits.
That being said, loose terminals causing the 1-2 correlation in the APP or the TP sensor circuits is so common GM released a PI for this concern, PIP3783D.

If you replace loose terminals, do not use crimp style butt connectors to fix, the problem will come back. Solder in connections have the least resistance and will fix it permanently.

Not saying this is your problem but it would be worth a look!

[TRStech]

I can confirm. APP correlation is extremely sensitive. Unplugging and reconecting any connector between APP sensor and ECU, even moving arround the harness a little, can be enough to cure a slightly corroded pin or terminal to make the difference. If you search the issue throughout the wiring, probaility is high that you ratteled the correct connection and cured it without noticing. Had a comparable phenomenon. Soldering every single terminal and in addition taking out and hardwiring any unnecessary interconnection would be the closest to bullet proof solution, but also a bunch of effort.

[blindsquirrel]

Most GM vehicles with a modern TAC control have an APP assembly has 6 wires and each individual APP sensor has a 5V ref, low ref and a signal wire.
This is the schematic for the 2008 Tahoe TAC and APP circuits.
1906839.png

So if you have high resistance on one of the low ref circuits, your 1-2 correlation will be off. Or high resistance on any of the individual circuits.
That being said, loose terminals causing the 1-2 correlation in the APP or the TP sensor circuits is so common GM released a PI for this concern, PIP3783D.

If you replace loose terminals, do not use crimp style butt connectors to fix, the problem will come back. Solder in connections have the least resistance and will fix it permanently.

Not saying this is your problem but it would be worth a look!

Concede your point about the pinout. I was seeing the 6-pin throttle body wiring in my head as that's where most of the problems/questions come up.

But still. It would have to be an intermittent high resistance on the loref, I'm still sticking to that. No other way to get higher voltage out of a potentiometer. I realize whatever the true solution turned out to be would already be firmly in the 'highly unlikely' category so 'double highly unlikely' isn't impossible. If the symptom were lower voltage than what it should be, that could be caused by either of two pins. Higher voltage could only be caused by one of the three.

(also, solder and multistranded wire and high vibration environments are a bad combination - dry uninsulated crimps and dual wall heat shrink in anything I work on)

[cadillactech]

Concede your point about the pinout. I was seeing the 6-pin throttle body wiring in my head as that's where most of the problems/questions come up.

But still. It would have to be an intermittent high resistance on the loref, I'm still sticking to that. No other way to get higher voltage out of a potentiometer. I realize whatever the true solution turned out to be would already be firmly in the 'highly unlikely' category so 'double highly unlikely' isn't impossible. If the symptom were lower voltage than what it should be, that could be caused by either of two pins. Higher voltage could only be caused by one of the three.

(also, solder and multistranded wire and high vibration environments are a bad combination - dry uninsulated crimps and dual wall heat shrink in anything I work on)

Oh ya no worries there, just wanted to make sure the OP knows what could also be causing his issue. Seen it hundreds of times.
I am not sure what is the actual cause, just throwing my experience out there for him so check, plus pin tension is so easy to check.

I have seen every "crimped" repair on this type of circuit fail. The crimped connections under the hood fail after the crimps go through a few heat cycles. The one in the car take a little bit longer. They lose tension over time and create a voltage drop. Eventually it is enough to cause an issue. Circuits like this are so sensitive that .025V drop can cause an issue.

Yes solder and high vibration can cause issues if done incorrectly, seen that a bunch of times. That is why you must always strain relief your wiring repairs, use only the minimum amount of solder to make the connection, do them in a straight section and co-axially wrap fabric tape to support the wiring harness.

GM actually makes a really good "crimp" sleeve that is meant for solder. GM made these specifically for these types of circuits to repair. You crimp the two wires with the OEM tool, then there is a hole in the crimp connector that you can add solder too. Add you weather proof heat shrink over that and you have a bulletproof repair.

If you want, PM me and I can give you the info on those.

That being said, this is an 08 Tahoe so the vibration inside the cabin is minimal compared to race car or other high stress environment.

If this were a race car or a built street car I would just string new wires end to end because I am that OCD.

I am curious if the issue comes back after his battery reset.

[mach]

Oh ya no worries there, just wanted to make sure the OP knows what could also be causing his issue. Seen it hundreds of times.
I am not sure what is the actual cause, just throwing my experience out there for him so check, plus pin tension is so easy to check.

I have seen every "crimped" repair on this type of circuit fail. The crimped connections under the hood fail after the crimps go through a few heat cycles. The one in the car take a little bit longer. They lose tension over time and create a voltage drop. Eventually it is enough to cause an issue. Circuits like this are so sensitive that .025V drop can cause an issue.

Yes solder and high vibration can cause issues if done incorrectly, seen that a bunch of times. That is why you must always strain relief your wiring repairs, use only the minimum amount of solder to make the connection, do them in a straight section and co-axially wrap fabric tape to support the wiring harness.

GM actually makes a really good "crimp" sleeve that is meant for solder. GM made these specifically for these types of circuits to repair. You crimp the two wires with the OEM tool, then there is a hole in the crimp connector that you can add solder too. Add you weather proof heat shrink over that and you have a bulletproof repair.

If you want, PM me and I can give you the info on those.

That being said, this is an 08 Tahoe so the vibration inside the cabin is minimal compared to race car or other high stress environment.

If this were a race car or a built street car I would just string new wires end to end because I am that OCD.

I am curious if the issue comes back after his battery reset.

still driving. still no issue. it has only happened right after tuning. the day i posted this, it would code out within 4 seconds of key on or code clearing. every time. only when i reset battery, did it go away. and stayed that way until i flashed again. then i reset again, and touched nothing. been fine ever since. couple hundred miles so far.