Throttle sensor error p2138 - Reduced engine power, Service traction system
Thread Starter
Racer
Joined: Aug 2007
Posts: 443
Likes: 37
From: LA CA
Throttle sensor error p2138 - Reduced engine power, Service traction system
This is the accelerator pedal sensor issue (APP), NOT the throttle body sensor (TPS) or steering angle sensor.
P2138 - Accel Pedal Pos (APP) Sensor 1-2 Correlation.
Whoever's had this before, how did you fix it?
I've tried jiggling the connections at the throttle pedal and at the ecu under the passenger fender. Took off the connectors, sprayed electrical contact cleaner on them, jiggled them a lot to break up any possible oxidation, but the behavior never changes. I get the power cut usually within 20 miles, sometimes earlier, sometimes later, depending on how I drive. Using cruise control I can avoid it longer. It's been nagging me for over a year now.
I think I need to replace the throttle pedal assembly, but I thought I'd shoot off this post in case I missed something, a connection between the throttle and ecu that I didn't check.
Thanks, guys!
P2138 - Accel Pedal Pos (APP) Sensor 1-2 Correlation.
Whoever's had this before, how did you fix it?
I've tried jiggling the connections at the throttle pedal and at the ecu under the passenger fender. Took off the connectors, sprayed electrical contact cleaner on them, jiggled them a lot to break up any possible oxidation, but the behavior never changes. I get the power cut usually within 20 miles, sometimes earlier, sometimes later, depending on how I drive. Using cruise control I can avoid it longer. It's been nagging me for over a year now.
I think I need to replace the throttle pedal assembly, but I thought I'd shoot off this post in case I missed something, a connection between the throttle and ecu that I didn't check.
Thanks, guys!
Last edited by steel_3d; Nov 8, 2009 at 02:20 PM.
Thread Starter
Racer
Joined: Aug 2007
Posts: 443
Likes: 37
From: LA CA
Wow, that's a weird connection. I guess it could be a voltage problem freaking out the ecu. Maybe I should get a data logger after all and see if other things like supply voltage are changing at the same time as the throttle issue happens.
Melting Slicks
Joined: Nov 2005
Posts: 2,345
Likes: 2
From: Houston 06 C6 Ysi SC 402 fgd TX
my cause was difficult to find. my car has been worked on a lot and somehow the brown wire from ECU to TB harness had a short at the ECU.
On the guys that add a KennyBell boost a pump if the fuse goes you get the reduced power error
check this thread out, there are more like it
http://forums.corvetteforum.com/c6-t...dling-but.html
On the guys that add a KennyBell boost a pump if the fuse goes you get the reduced power error
check this thread out, there are more like it
http://forums.corvetteforum.com/c6-t...dling-but.html
Last edited by drivinfast; Nov 4, 2009 at 10:00 PM.
Pro
Joined: May 2000
Posts: 610
Likes: 1
From: Midland Texas
St. Jude Donor '09-'11
Check the wiring at the throttle position sensor. It sits right above the fan belt. If the fan belt starts to fray, the fray will slap the wiring and can damage the wires causing limp mode. I had to fix this once on an instructors car at a track day event.
I know this is a long shot, but it won't take a minute to check to see if the wiring is damaged right above the belt.
Joe
I know this is a long shot, but it won't take a minute to check to see if the wiring is damaged right above the belt.
Joe
Thread Starter
Racer
Joined: Aug 2007
Posts: 443
Likes: 37
From: LA CA
Thanks, guys. But those are different issues than "P2138 Accel Pedal Pos (APP) Sensor 1-2 Correlation". This has to do with at least one of the pedal position sensor readings not agreeing with the rest (there are 3 I believe).
The problems you guys refer to are TPS (the one at the throttle body) and steering angle sensors respectively.
The problems you guys refer to are TPS (the one at the throttle body) and steering angle sensors respectively.
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Pro
Joined: May 2000
Posts: 610
Likes: 1
From: Midland Texas
St. Jude Donor '09-'11
Thanks, guys. But those are different issues than "P2138 Accel Pedal Pos (APP) Sensor 1-2 Correlation". This has to do with at least one of the pedal position sensor readings not agreeing with the rest (there are 3 I believe).
The problems you guys refer to are TPS (the one at the throttle body) and steering angle sensors respectively.
The problems you guys refer to are TPS (the one at the throttle body) and steering angle sensors respectively.
Racer
Joined: Jan 2010
Posts: 293
Likes: 2
From: Atlanta Georgia
This is the accelerator pedal sensor issue (APP), NOT the throttle body sensor (TPS) or steering angle sensor.
P2138 - Accel Pedal Pos (APP) Sensor 1-2 Correlation.
Whoever's had this before, how did you fix it?
I've tried jiggling the connections at the throttle pedal and at the ecu under the passenger fender. Took off the connectors, sprayed electrical contact cleaner on them, jiggled them a lot to break up any possible oxidation, but the behavior never changes. I get the power cut usually within 20 miles, sometimes earlier, sometimes later, depending on how I drive. Using cruise control I can avoid it longer. It's been nagging me for over a year now.
I think I need to replace the throttle pedal assembly, but I thought I'd shoot off this post in case I missed something, a connection between the throttle and ecu that I didn't check.
Thanks, guys!
P2138 - Accel Pedal Pos (APP) Sensor 1-2 Correlation.
Whoever's had this before, how did you fix it?
I've tried jiggling the connections at the throttle pedal and at the ecu under the passenger fender. Took off the connectors, sprayed electrical contact cleaner on them, jiggled them a lot to break up any possible oxidation, but the behavior never changes. I get the power cut usually within 20 miles, sometimes earlier, sometimes later, depending on how I drive. Using cruise control I can avoid it longer. It's been nagging me for over a year now.
I think I need to replace the throttle pedal assembly, but I thought I'd shoot off this post in case I missed something, a connection between the throttle and ecu that I didn't check.
Thanks, guys!
1) Checked contunity and resistances from APP to ECM.
2) Checked connections as TB and APP
3) Replaced APP
4) Upgraded alternator (needed it anyway due to electric WP and amp)
5) Ran 0 gauge wire directly from alternator to fuse box
6) Replaced fuse box (needed it anyway as some fuse slots were loose)
7) Reflashed ECM to stock (tuned due to changed headers and exhaust)
8) Cleaned random grounds.
If you havent fixed it, please tell me every single thing that isnt stock and everything that you have ever had problems with so that it can help us get this fixed. If it has been fixed and youre not sure what fixed it, please name everything youve tried. Ive had this problem for a while and its really getting old.
Thanks,
Josh
Thread Starter
Racer
Joined: Aug 2007
Posts: 443
Likes: 37
From: LA CA
Wow, should've updated this thread. My problem got so bad eventually, that I couldn't drive 10 minutes on the highway without tripping the code. I had to constantly play with the throttle, but in some situations that wasn't feasible and it would trip. I believe there was a dead spot in the pot at low throttle angle, ie highway cruising angle.
Dealer replaced the accelerator pedal, and never had a problem since. That was 30k miles ago.
I tried running all kinds of ground wires, even hooked up a big cap trying to smooth out any electrical spikes, but of course it was all useless since the pedal was bad.
I would try swapping a known good pedal out of another car. It's a quick swap.
You're positive you're getting p2138 not something else? I got a few random codes in addition, probably caused by the bad throttle signal, but p2138 was the main one. Never had any codes since the pedal was replaced.
Good luck, let us know how it goes.
Dealer replaced the accelerator pedal, and never had a problem since. That was 30k miles ago.
I tried running all kinds of ground wires, even hooked up a big cap trying to smooth out any electrical spikes, but of course it was all useless since the pedal was bad.
I would try swapping a known good pedal out of another car. It's a quick swap.
You're positive you're getting p2138 not something else? I got a few random codes in addition, probably caused by the bad throttle signal, but p2138 was the main one. Never had any codes since the pedal was replaced.
Good luck, let us know how it goes.
Racer
Joined: Jan 2010
Posts: 293
Likes: 2
From: Atlanta Georgia
I'm glad you got it fixed. However, I have replaced the APP unit with no luck so I sold it on the forum and put the old one back on. Yes I'm sure it's P2138. Like you, I have had other pedal relalated codes as well as others unrelated to pedal but P2138 is the primary code and trips most often BY FAR. Glad you got it fixed. I'll keep working on mine.
Josh
Josh
Thread Starter
Racer
Joined: Aug 2007
Posts: 443
Likes: 37
From: LA CA
Has the other forum member confirmed that the "new" pedal was perfect? If you were getting the code with a KNOWN GOOD pedal, then you're pretty screwed 
Have you made sure the ECU connectors are clean (under the passenger fender)? I'm guessing you have since you checked continuity.
In your place I would get a data logger that has the full assortment of GM PIDs, which include the individual APP sensor signals. Also gotta make sure the logger can sample a few signals at least at 10 frames per second. Then hopefully you'll catch any irregularities, either in individual pot voltage, or supply voltage. I have another thread where some decent loggers were suggested, but I haven't tried any of them.
That was my plan till I decided to just take it in under warranty. My car is stock. That reminds me, the dealership replaced the APP right away. Not sure if it was due to something their magic Tech 2 told them, or they did it for lack of a better idea, but maybe the Tech 2 knows something we don't... Something to consider.
Have you made sure the ECU connectors are clean (under the passenger fender)? I'm guessing you have since you checked continuity.
In your place I would get a data logger that has the full assortment of GM PIDs, which include the individual APP sensor signals. Also gotta make sure the logger can sample a few signals at least at 10 frames per second. Then hopefully you'll catch any irregularities, either in individual pot voltage, or supply voltage. I have another thread where some decent loggers were suggested, but I haven't tried any of them.
That was my plan till I decided to just take it in under warranty. My car is stock. That reminds me, the dealership replaced the APP right away. Not sure if it was due to something their magic Tech 2 told them, or they did it for lack of a better idea, but maybe the Tech 2 knows something we don't... Something to consider.
Racer
Joined: Jan 2010
Posts: 293
Likes: 2
From: Atlanta Georgia
I purchased the APP new at dealer. I sold it on forum when it didn't fix the issue. I have checked the connectors at ecu. I now have an incredible data logger so I will find it, eventually. Just trying to see what others did to fix issue.
Tech Contributor
Joined: Oct 1999
Posts: 41,058
Likes: 9,821
From: Charlotte, NC (formerly Endicott, NY)
The Tech 2 gives them voltage readings and they also use the diagnostic procedure to find the failed element. P2138 is not a code that directs a person to replace the APP it is a code that gets you in the vicinity of the failure and allows a person with the correct tools and diagnostic procedure to figure out what is wrong.
The problem is in the APP, the ECM or the wiring between the two. If you are good with a DVM you can check some of the same things the Tech 2 checks and maybe isolate the bad part.
If you don't have the diagnostic procedure here are the relevant parts.
Circuit/System Verification
1. Ignition ON, observe the scan tool APP sensor 1 voltage parameter. The reading should be between 0.32-4.75 volts, and change with accelerator pedal input.
2. Ignition ON, observe the scan tool APP sensors 2 voltage parameter. The reading should be between 0.32-4.75 volts and change with accelerator pedal input.
3. Ignition ON, observe the scan tool APP sensors 1 and 2 parameter. The scan tool should indicate agree.
4. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.
5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the accelerator pedal. Allow at least 60 seconds for the ECM to power down. This can be verified by a loss of communication message on the scan tool.
2. Test for less than 5 ohms of resistance between each low reference circuit terminals A and D and ground.
⇒ If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
3. Ignition ON, test for 4.8-5.8 volts between each 5-volt reference circuit terminals C and F and ground.
⇒ If less than 4.8 volts, test the affected 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
⇒ If greater than 5.2 volts, test the affected 5-volt reference circuit for short to voltage. If the circuit test normal, replace the ECM.
4. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1 volt.
⇒ If greater than 0.1 volt, test the APP sensor 1 and 2 signal circuits terminals B and E for a short to voltage. If the circuit tests normal, replace the ECM.
5. Install a 3A fused jumper wire between the signal circuit terminal E and the 5-volt reference circuit terminal F of the APP sensor 1. Verify the scan tool parameter APP sensor 1 voltage is greater than 4.8 volts.
⇒ If less than 4.8 volts, test the APP sensor 1 signal circuit for an open or short to ground. If the circuit tests normal, replace the ECM.
6. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal C of the APP sensor 2. Verify that the scan tool parameter APP sensor 2 voltage is greater than 4.8 volts.
⇒ If less than 4.8 volts, test the APP sensor 2 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
7. Ignition OFF, disconnect the harness connector at the ECM.
8. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:
• ECM X1 signal circuit terminal 29 to APP terminal E
• ECM X1 signal circuit terminal 32 to APP terminal B
• ECM X1 5-volt reference circuit terminal 36 to APP terminal C
• ECM X1 5-volt reference circuit terminal 56 to APP terminal F
⇒ If greater than 5 ohms, repair the affected circuit for an open/high resistance.
9. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.
⇒ If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuits.
10. If all circuits test normal, test the APP sensor. Refer to Component Testing for instructions.
⇒ If the APP sensor tests normal, replace the ECM.
Component Test
Important: The Circuit/System Testing must be performed before proceeding with the Component Test.
Dynamic Test
1. Install a 3A fused jumper wire between the 5-volt reference terminal of the applicable APP sensor and 5 volts. Install a jumper wire between the low reference terminal and a ground.
2. Sweep the sensor through the entire range while monitoring the voltage between the signal terminal and the low reference terminal with a DMM. The voltage should vary between 0.30-4.98 volts without any spikes or dropouts.
⇒ If the voltage is not within the specified range or is erratic, replace the accelerator pedal assembly.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• Accelerator Pedal Position Sensor Replacement
• Control Module References for ECM replacement, setup, and programming
Bill
The problem is in the APP, the ECM or the wiring between the two. If you are good with a DVM you can check some of the same things the Tech 2 checks and maybe isolate the bad part.
If you don't have the diagnostic procedure here are the relevant parts.
Circuit/System Verification
1. Ignition ON, observe the scan tool APP sensor 1 voltage parameter. The reading should be between 0.32-4.75 volts, and change with accelerator pedal input.
2. Ignition ON, observe the scan tool APP sensors 2 voltage parameter. The reading should be between 0.32-4.75 volts and change with accelerator pedal input.
3. Ignition ON, observe the scan tool APP sensors 1 and 2 parameter. The scan tool should indicate agree.
4. Clear the DTCs with the scan tool. Operate the vehicle within the Conditions for Running the DTC, or within the conditions that you observed from the Freeze Frame/Failure Records.
5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the accelerator pedal. Allow at least 60 seconds for the ECM to power down. This can be verified by a loss of communication message on the scan tool.
2. Test for less than 5 ohms of resistance between each low reference circuit terminals A and D and ground.
⇒ If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
3. Ignition ON, test for 4.8-5.8 volts between each 5-volt reference circuit terminals C and F and ground.
⇒ If less than 4.8 volts, test the affected 5-volt reference circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
⇒ If greater than 5.2 volts, test the affected 5-volt reference circuit for short to voltage. If the circuit test normal, replace the ECM.
4. Ignition ON, verify the scan tool APP sensor 1 and 2 voltages are less than 0.1 volt.
⇒ If greater than 0.1 volt, test the APP sensor 1 and 2 signal circuits terminals B and E for a short to voltage. If the circuit tests normal, replace the ECM.
5. Install a 3A fused jumper wire between the signal circuit terminal E and the 5-volt reference circuit terminal F of the APP sensor 1. Verify the scan tool parameter APP sensor 1 voltage is greater than 4.8 volts.
⇒ If less than 4.8 volts, test the APP sensor 1 signal circuit for an open or short to ground. If the circuit tests normal, replace the ECM.
6. Install a 3A fused jumper wire between the signal circuit terminal B and the 5-volt reference circuit terminal C of the APP sensor 2. Verify that the scan tool parameter APP sensor 2 voltage is greater than 4.8 volts.
⇒ If less than 4.8 volts, test the APP sensor 2 signal circuit for an open/high resistance or short to ground. If the circuit tests normal, replace the ECM.
7. Ignition OFF, disconnect the harness connector at the ECM.
8. Test for less than 5 ohms of resistance on all APP sensor circuits between the following terminals:
• ECM X1 signal circuit terminal 29 to APP terminal E
• ECM X1 signal circuit terminal 32 to APP terminal B
• ECM X1 5-volt reference circuit terminal 36 to APP terminal C
• ECM X1 5-volt reference circuit terminal 56 to APP terminal F
⇒ If greater than 5 ohms, repair the affected circuit for an open/high resistance.
9. Test for infinite resistance between APP sensor 1 signal circuit terminal E and APP sensor 2 signal circuit terminal B.
⇒ If less than infinite resistance, repair the short between APP sensor 1 signal circuit and APP sensor 2 signal circuits.
10. If all circuits test normal, test the APP sensor. Refer to Component Testing for instructions.
⇒ If the APP sensor tests normal, replace the ECM.
Component Test
Important: The Circuit/System Testing must be performed before proceeding with the Component Test.
Dynamic Test
1. Install a 3A fused jumper wire between the 5-volt reference terminal of the applicable APP sensor and 5 volts. Install a jumper wire between the low reference terminal and a ground.
2. Sweep the sensor through the entire range while monitoring the voltage between the signal terminal and the low reference terminal with a DMM. The voltage should vary between 0.30-4.98 volts without any spikes or dropouts.
⇒ If the voltage is not within the specified range or is erratic, replace the accelerator pedal assembly.
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
• Accelerator Pedal Position Sensor Replacement
• Control Module References for ECM replacement, setup, and programming
Bill
1st Gear
Joined: Apr 2012
Posts: 1
Likes: 0
Hey steel_3d, I am having the same problem with the codes P2138 and P1125 in my 2005 Grand Prix GT, I have change wires, battery, base controle module, even I change the car's computer... and the problem is not resolved.
what I am doing for the last year, is deleting the codes so at least I can drive fine for one month.
Now I am tired of this, I can't even sell my car with this problem...
when you changed the accelerator pedal, it work?
or you are having the reduced engine power again?
PLEASEEEE help me!!!
what I am doing for the last year, is deleting the codes so at least I can drive fine for one month.
Now I am tired of this, I can't even sell my car with this problem...
when you changed the accelerator pedal, it work?
or you are having the reduced engine power again?
PLEASEEEE help me!!!