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#1 |
![]() Drives: 2012 LFX Chevrolet Camaro Join Date: Feb 2024
Location: England
Posts: 6
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P2138 and Reduced Engine Power
Hello all,
Camaro owner from the UK experiencing a fair few issues right now. Firstly, the car has previously had a P2138 which was resolved with a new APP (accelerator pedal position sensor). Since then the issue has come back around with the exact same P2138 and reduced engine power, despite my disbelief of my almost brand new APP going bad I got a new one anyway, which did not resolve the issue. The P2138 and reduced engine power will only come up once I hit the kick down part of the gas pedal, although, 1/10 times the fault will not flash up, the other 9/10 times are the problem. Since then I have now replaced my throttle body and even wired in a new throttle body pigtail (I am an electrician). I know everything has been installed correctly but I am still encountering the exact same issues. It is also worth noting the issue will come up whether the engine is on or off. Can someone provide any advice on what else to check as I don't fancy taking the chance of spending £600+ on a new PCM/ECM. If anybody has links or PDFs to wiring diagrams from the PCM to the throttle body and pedal that would be grand as Google doesn't seem to be very helpful right now. Any help would be much appreciated. Thanks all! |
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#2 |
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() Drives: 2010 Camaro SS2,L99, LSA SC Join Date: Aug 2017
Location: Huntsville, AL
Posts: 2,280
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Full diagnostics are available for a reasonable fee from alldata.com or with an acdelco tds subscription (assuming these are available outside the US).
I think the P2138 is one of the tricky ones that is checking correlation between rising and falling voltages across both the accelerator pedal sensor and the throttle position sensor. And if its an intermittent problem, it will probably be be hard to track down the problem. And next to impossible to track down without something to pull freeze frame data from when the code triggered. Do you have a throttle commander or similar connected or has the car been "tuned"? |
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#3 | |
![]() Drives: 2012 LFX Chevrolet Camaro Join Date: Feb 2024
Location: England
Posts: 6
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Quote:
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#4 |
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() Drives: 2010 Camaro SS2,L99, LSA SC Join Date: Aug 2017
Location: Huntsville, AL
Posts: 2,280
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How long have you had the car? A lot of driving and then out of the blue problem or is this a recent purchase that has pretty much done it from day 1.
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#5 |
![]() Drives: 2012 LFX Chevrolet Camaro Join Date: Feb 2024
Location: England
Posts: 6
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I've owned it for about 14 months now, fault code appeared about 2-3 months ago out of the blue, done track days and road trips but nothing particular comes to mind occurring within about a month of the fault coming up.
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#6 |
![]() ![]() ![]() ![]() ![]() ![]() ![]() ![]() Drives: 2010 Camaro SS2,L99, LSA SC Join Date: Aug 2017
Location: Huntsville, AL
Posts: 2,280
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This will probably take using the factory diagnostic steps from the sites I mentioned to determine what the problem is. If the fault is constant, it shouldn't be to hard for someone with a decent diagnostics scanner, wiring diagrams and factory diagnostic steps. Without those, probably impossible. But you might be able to do it with a DVM, depending on the exact diagnostic procedure.
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#7 |
![]() Drives: 2011 2SS, 2006 GMC Sierra Join Date: Jul 2019
Location: MA
Posts: 292
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Is there anything connected to the APP circuits? like a pedal commander etc....If there is disconnect it and re-test, There's a 40 cavity connector X104 located under the brake booster area, Its rectangular, Pull that apart and see if there is any water intrusion, corrosion etc.... The other that's also a 40 cavity rectangular X102 is located RF, I think its beside the PDC(underhood fuse block). Also if u have a DVOM u can check the circuits starting at the APP sensor connector. You would check for 5V reference on C(TAN) and F(WH/BK) KOEO. Check for less than 5 ohms on A(Purple) and D(BN). For reference A is purple and F is white/black, Its a 6 cavity connector. Likely have high resistance in a circuit which would affect a voltage/low reference circuit.
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#8 |
![]() Drives: 15SS Camaro Join Date: Dec 2020
Location: US
Posts: 351
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1st thing I would do is remove all the connecters at the PCM and look for corrosion and reseat everything. Next would be to reseat ALL connections in that circuit and look for corrosion-damage. Then maybe move on to testing wiring for damage. The PCM could also be the cause but I wouldn't replace it until you test everything 1st.
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#9 |
![]() Drives: 2011 2SS, 2006 GMC Sierra Join Date: Jul 2019
Location: MA
Posts: 292
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Any word on a fix or progress?
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#10 |
![]() Drives: 2012 LFX Chevrolet Camaro Join Date: Feb 2024
Location: England
Posts: 6
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Update:
No fix as of yet, my local garage tested my pedals and my pinouts and found the pedals to be faulty, to which I tested them myself and they all tested no issues at all. I've even tested supply and feedback voltages at the pedal with a digital voltmeter which measured no issues. I ordered another off-brand GM pedal which once again I've tested as working but still have P2138. I have found by resetting my ECM (disconnecting battery) the car acts right for up to about 30-45 minutes before going back into fault when hard accelerating. Graphing the data D/E voltages on the pedals it shows they're working absolutely fine so I can only guess the formula to calculate P2138 has corrupted in some kind of way. I'm now killing the car over night to see if it can completely reset the ECM before I go to the local tuner and see if they can program P2138 out of the car. And for reference 4 OBDII scanners have all proven the only fault is a P2138 D/E voltage correlation.
Last edited by Cbrowne; 04-08-2024 at 01:27 PM. |
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#11 |
![]() Drives: 2012 LFX Chevrolet Camaro Join Date: Feb 2024
Location: England
Posts: 6
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Update 2:
A bit of an update, I have now found after killing the car it operates with no issues at all for all of about 30 minutes. No amount of driving with a lead foot will bring up the P2138...until 30 minutes later. After the 30 minutes the issue comes back. What I have found is; in the 30 minutes my D/E voltages correlate exactly as they should. I.e:
Sensor 1 20% = Sensor 2 10% Sensor 1 40% = Sensor 2 20% Sensor 1 60% = Sensor 2 30% etc. However, after the 30 minutes, it goes to: Sensor 1 20% = Sensor 2 12% Sensor 1 40% = Sensor 2 24% Sensor 1 60% = Sensor 2 36% Although, once this has set in, it stays like this until the ECM is reset. I've tried to test the connectors/looms by wriggling them vigorously to see any voltage drops/increases on the D/E graphs but they show nothing out of the ordinary. So far it seems that once the ECM is set in it cannot read the voltages right, I have proven that there is a constant 5V to each sensor with a DVM and proven a consistent feedback voltage is outputted through the APP sensor. Although, without a proper voltage % table I couldn't tell you if it is correct or not, all I know is it's consistent. Right now I'm guessing there can be 2 causes, a voltage is being induced into one of the cables from the loom, or the ECM itself is creating some kind of interference once fully energised. What does everyone else think? I'm going to test the circuit resistance once again to see if anything has changed, but from what I remember from doing it a while ago all was fine and bang on specification. |
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#12 |
![]() Drives: 2012 LFX Chevrolet Camaro Join Date: Feb 2024
Location: England
Posts: 6
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Update 3:
I've done some more investigative work and have a few measured values.
Firstly, each cable from the APP to the ECM is reading 0.2 Ohms, no shorts and no open circuits. Secondly, the outputs from the APP are as follows: At 0% throttle - Sensor 1 = 0.958V and Sensor 2 = 0.482V 99.9% accurate At 100% throttle - Sensor 1 = 3.852V and Sensor 2 = 1.924V 99.9% accurate However, the ECM is reading: At 0% throttle - Sensor 1 = 21% and Sensor 2 = 10% 95% accurate At 100% throttle - Sensor 1 = 79.5% and Sensor 2 = 42.75% 93% accurate What I believe is happening is as sensor 1 is increasing if it doesn't quite reach the 90% accurate threshold of sensor 2 then it will go into P2138 fault. Next step will be to power up a programmable 5V power supply and look for any voltage drop between the pedal and the ECM plugs. What I have also found by shorting out the APP is that sensor 1 can only reach a max of 90% whereas sensor 2 goes straight to 100%. In addition to this, sensor 1 doesn't go straight to 90%, it typically reaches 85% before incrementally going to 90%. It is definitely leaning towards my ECM going bad so will get some quotes through for a clone and looking at swapping them out. |
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#13 |
![]() Drives: 2012 camaro convertible in orange Join Date: Nov 2014
Location: United Kingdom
Posts: 1
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Hi , I'm in the same place as you and your car and in UK bought new pedal and t body last year after a few tries to reset I took it to a tuner who reset it and all good parked up Nov to April and it only ran OK for a few short trips but went into limp again same code took to same guy who said it looks like t body again so put old one back on and reset and all good 3 short trips and it's gone limp again today says service stabiltrack this I'm lost and depressed
Hope you find the cure , Richard 07752070059 |
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