P2127 Code or P2138 Code Chevrolet

How to diagnose and fix P2127 Chevrolet or P2138 Chevrolet trouble codes

Shops are reporting a high incidence of P2127 Chevrolet or P2138 Chevrolet trouble codes and the problem can be a wiring harness issue at the accelerator pedal position sensor OR at the throttle body. Don’t automatically assume the components are bad unless you like throwing parts around.

Here are the codes and the criteria for setting:

Code definition: P2127- Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage

Criteria: The ECM detects that the APP sensor 2 voltage is less than 0.325 volt for more than 0.4 second.

Code definition: P2138- Accelerator Pedal Position (APP) Sensor 2 Circuit Low Voltage

Criteria: The voltage difference between APP sensor 1 and APP sensor 2 exceeds a predetermined value for more than 2 seconds.

Accelerator pedal position sensor assembly

From the troubleshooting section of the shop manual, here’s what to look for:

APP Sensor 1 Signal code: If you have code P2138 check for High resistance

APP Sensor 1 5-Volt Reference If you have code P2138 check for High resistance

APP Sensor 1 Low Reference If you have code P2138 check for High resistance

APP Sensor 2 Signal If you have code P2127 check for Short to Ground

If you have code P2138 check for High resistance, If you have code P2127 check for open in circuit

APP Sensor 2 5-Volt Reference If you have code P2127 check for Short to Ground  If you have code P2138 check for High resistance

If you have code P2127 check for open in circuit

APP Sensor 2 Low Reference – If you have code P2138 check for High resistance

P2127 and P2138 testing values:

APP Sensor 1 Signal:  Normal range is: 0.33-4.75V, Short to ground would read 0V, Open or high resistance would read 0V, Short to voltage would read 5V

APP Sensor 1 5-Volt Reference: Normal range is: 0.33-4.75V, Short to ground would read 0V,  Open or high resistance would read 0V, Short to voltage would read 5V

APP Sensor 1 Low Reference: Normal range is: 0.33-4.75V – 4.96V

APP Sensor 2 Signal: Normal range is: 0.33-2.50V, Short to ground would read 0V, Open or high resistance would read 0v, Short to voltage would read 5V

APP Sensor 2 5-Volt Reference: Normal range is: 0.33-2.50V,  Short to ground would read 0V, Open or high resistance would read 0v, Short to voltage would read 5V

APP Sensor 2 low Reference: Normal range is: 0.33-2.50 V, Open or high resistance would read 4.92 V

If there is no problem found, inspect C109/X109 and C205/X205 for the following concerns:

GM has issued a service bulletin on this problem and the bulleting advises to check these items:

• Check for connector halves that are not seated properly
• Corrosion and/or water intrusion
• APP circuit terminals that are not seated properly
• APP circuit terminals that have poor terminal tension using the correct terminal test probes
• APP circuit terminals that are not crimped properly

Check connector C109/X109 located on the left side of the engine compartment below the underhood fuse block

Check connector C205/X205 located under the Upper Instrument Trim Panel. To access C205/X205, follow the Instrument Panel Upper Trim Panel with Windshield Defroster Nozzle Grille Replacement Procedure in SI.

Shops are reporting wire breaks at the APP and at the electronic throttle body due to a stretched harness. Check with the dealer to see if a new harness is available before trying to repair the existing harness.

©, 2016 Rick Muscoplat