2008 Chevrolet Impala



December, 27, 2012 AT 6:39 PM

My service traction control and RPMs being reduced message has been coming on for over a week. I replaced the right front box hub because of a broken wire and it started in again

I found this post but what could it be?

The first thing a mechanic should look for is any damage to any wiring harnesses (there is a Technical Service Bulletin out about this).

If it isn't a voltage issue or the wire harnesses, then the next two things to look at would be your Throttle Position Sensor (requires replacing the throttle body) and the Accelerator Position Sensor (requires replacing your gas pedal).

The system in the Impalas is called a "Drive-by-wire" system. This means the accelerator position sensor and throttle position sensor work together. If either one of them act up, you get the warning messages you are seeing.

After changing any of these parts a relearn procedure must also be done so that the computer can relearn (or adjust) to the newer parts.

I opted to change my throttle body first, ooops. It turned out to be the accelerator (which is the cheaper part to replace by the way). Now it's running normally.


3 Answers



December, 27, 2012 AT 6:40 PM

Scan for codes first


2CarPros Mike

December, 30, 2012 AT 12:11 AM

Code 2127

Sent from my iPhone



December, 30, 2012 AT 1:25 AM

This can be a bad ecm but you need a protype tester to really see what is going on, it may be a bad wire that is shorted to ground or a bad connection. It needs the pro tpe so it can test one side the app 2 side of the throttle pedal assy. This is what the tsb says as well.

This condition may be caused by water intrusion into the instrument panel (IP) to body harness connector, which carries the APP sensor signals to the ECM/PCM. This water intrusion results in a voltage difference between
APP Sensor 1 and APP Sensor 2 that exceeds a predetermined value for more than a calibrated period of time, setting P2138.


NOTE: Aftermarket equipment can generate DTC P2138 and/or other DTCs.

1. Verify that aftermarket equipment is not electrically connected to any of the APP sensor signal or low reference circuits or to any other ECM/PCM 5V reference or low reference circuits. Refer to Checking Aftermarket
Accessories in SI.
2. Perform the Diagnostic System Check Vehicle.
3. If any 5V reference DTCs are set, refer to Diagnostic Trouble Code (DTC) List Vehicle.
4. If any 5V reference DTCs are not set, proceed to Step 3.
5. Locate the IP to body harness connector, which may be located in and around the left hand kick panel area or inside the IP. Depending on the vehicle and model year, refer to Wiring Systems or Power and Signal
Distribution in SI.

NOTE: Some examples of potential water leaks are: A pillar seals, sunroof drain lines (if equipped) and windshield/cowl sealing.

6. Inspect for a water leak in the area. If necessary use a water hose to determine the source of the leak. Refer to General Information > Water Leaks in SI.
7. If a water leak is observed, repair as necessary. Verify the effectiveness of the repair.
8. Inspect the IP to body harness connector terminals for corrosion and debris. Refer to Testing for Intermittent Conditions and Poor Connections in SI.
9. If any corrosion and/or debris is observed, repair as necessary.
10. After completing the repair, verify the proper operation of the system. Depending on the vehicle and model year, perform the Diagnostic Repair Verification procedure or refer to Diagnostic Trouble Code (DTC) List
Vehicle in SI.
This can also be caused by aftermarket stuff being put on car.

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