GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Saturn 🢒 2009 🢒 Astra 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0121, P0703, P0727, P1125, or P2637

Diagnostic Instructions
    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0121: Throttle Position (TP) Sensor Performance

DTC P0703: Brake Switch Circuit

DTC P0727: Engine Speed No Signal

DTC P1125: Accelerator Pedal Position (APP) System

DTC P2637: Transmission Torque Delivered Circuit

Circuit/System Description

The controller area network (CAN) serial data bus is used by the engine control module (ECM) and transmission control module (TCM) to share information. This diagnostic applies to ECM component failures that are communicated to the TCM.

Conditions for Running the DTC
    • No Lost Communications with the ECM, DTC U0100.
    • No Speed Sensor DTCs P0717 or P0722.
    • The ignition is ON for at least 2 seconds.
    • The input and engine speed is greater than 500 RPM.
    • Not in Emergency Mode.

Conditions for Setting the DTC

P0121

The TCM receives notification that the throttle position signal to the ECM is invalid for 4 seconds.

P0703

The TCM receives notification that the brake pedal signal to the ECM is invalid for 4 seconds.

P0727

The TCM receives notification that the engine speed signal to the ECM is invalid.

P1125

The TCM receives notification that the accelerator pedal position signal to the ECM is invalid for 4 seconds.

P2637

The TCM receives notification that the actual engine torque signal to the ECM is invalid for 4 seconds.

Action Taken When the DTC Sets

P0121 and P1125

    • DTC P0121 is a Type C DTC.
    • The transmission will operate in 4th gear in D range, Reverse in R range.

P0703

    • DTC P0703 is a Type C DTC.
    • The TCM will default the brake pedal signal to OFF.
    • The TCM will release TCC when input speed is less than 2000 RPM.
    • The TCM will inhibit adaptive shift control.
    • The TCM will inhibit neutral control.

P0727

    • DTC P0727 is a Type C DTC.
    • The TCM will default engine speed data to 0 RPM.
    • The transmission will operate in 4th gear in D range, Reverse in R range.

P2637

    • DTC P2637 is a Type C DTC.
    • The TCM will default engine torque data to 400 N·m (295 lb ft).
    • The transmission will operate in 4th gear in D range, Reverse in R range.

Conditions for Clearing the DTC

DTCs P0121, P0703, P0727, P01125, and P2637 are Type C DTCs.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Transmission General Information

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References

Circuit/System Verification
  1. Verify that there are no DTCs set in the ECM.
    2. ⇒If DTCs are set in the ECM, diagnose them first.
  2. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
    3. ⇒If the DTC resets, replace the ECM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for ECM replacement, setup, and programming