GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 HUMMER 🢒 2008 🢒 H3 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC C0240 or P0856

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 C0240: ECM Traction Control Not Allowed

DTC P0856: Traction Control Torque Request Circuit

Circuit/System Description

C0240

The engine control module (ECM) and the electronic brake control module (EBCM) communicate on the serial data link, whenever the ignition is ON.

P0856

The ECM supplies 5 volts through an internal resistor, to the EBCM on the requested torque signal circuit. The EBCM toggles this voltage to ground to create a valid requested torque signal at the ECM.

Conditions for Running the DTC

C0240

Ignition ON.

P0856

    • Ignition ON.
    • The engine is running at a speed greater than 450 RPM for 5-20 seconds.

Conditions for Setting the DTC

C0240

The EBCM receives a serial data message stating that the ECM has lost the ability to reduce engine torque.

P0856

The ECM receives an invalid requested torque signal for 3 seconds.

Action Taken When the DTC Sets

C0240

    • The EBCM disables the traction control system (TCS) and vehicle stability enhancement system (VSES).
    • A DIC message and/or a warning indicator may be displayed.

P0856

    • The ECM sends a serial data message to the EBCM stating that the ECM has lost the ability to reduce engine torque.
    • The EBCM sets DTC C0240 as a current DTC for as long as the malfunction is present.

Conditions for Clearing the DTC

C0240

The conditions for setting the DTC are no longer present.

P0856

    • The conditions for setting the DTC are no longer present.
    • A history DTC clears after 40 consecutive warm-up cycles without a ECM detected failure.

Reference Information

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

ABS Description and Operation

Electrical Information Reference

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

Scan Tool Reference

Control Module Referencesfor scan tool information.

Circuit/System Testing

Important: It is recommend that the defective components be replaced, and not the complete brake master cylinder assembly.

  1. Ignition OFF, disconnect the harness connector X2 at the EBCM.
  2. Ignition ON, test for 4.8-5.2 volts between the signal circuit terminal 9 and ground.
    3. ⇒If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
    ⇒If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
  3. If the circuits test normal, replace the EBCM.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for EBCM or ECM replacement, setup, and programming