C0278

DTC C0278
Circuit Description
The Brake Pedal Position (BPP) sensor provides an analog pedal position signal. Its output is hardwired to the Electro-Hydraulic Power Steering (EHPS) module connector. The signal must be digitized and differentiated within the EHPS module to provide the necessary pedal rate signal.

The BPP sensor is a resistive sensor with a total resistance between 3,000-5,000 ohms with a maximum current draw of less than 16 ma. The BPP sensor will output an analog signal that is referenced to 5 volts which may increase or decrease monotonically with brake pedal depression. The sensor analog output shall have a specified electrical output over a mechanical range of 32 degrees rotation of the brake pedal pivot. Out-of-range values will be provided outside of the 32 degrees range.

The EHPS provides a GMLAN message to the vehicle which indicates the translation of the brake pedal. Due to build variance, the EHPS cannot be certain what BPP sensor signal voltage represents a BPP at rest. The EHPS needs the 0 reference to provide BPP. The EHPS receives a Control Packet Identifier (CPID) request from a scan tool to calibrate the 0 reference position (learn home).

DTC C0278 can be set for the 2 following reasons:
^ A new EHPS has been installed. A traceability request or the ignition is cycled 255 times before receiving a learn home request.
^ The EHPS receives the learn home request and the BPP sensor is not within a valid range. If there is a hardware problem or the operators foot is on the pedal, the 0 reference read will not execute. Calibration of the BPP sensor is performed whenever the BPP sensor is replaced or the EHPS system has been serviced.

DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C0278 Brake Pedal Position Sensor Not Calibrated

Conditions for Running the DTC
^ The EHPS module is in the RUN mode.
^ The ignition switch is in the ACC or ON position.
^ Battery voltage is between 12-58 volts.

Conditions for Setting the DTC
The EHPS has never received a learn home command or when the learn home calibration is received. The difference between the BPP nominal position and the actual position is greater than 44.92 mm (1.76 inch) or is less than -44.92 mm (-1.76 inch).

Action Taken When the DTC Sets
^ System operation is reduced.
^ The SERVICE BRAKE SYSTEM message will be displayed.
^ Ramp the motor speed input to the commanded flow resolved from a default BPP.
^ Stores DTC C0282 in the Powertrain Control Module (PCM).
^ History DTC C0282 will be set in the PCM.

Conditions for Clearing the DTC
^ A successful learn home calibration has been performed.
^ Using the scan tool
^ A history DTC will clear after 255 consecutive ignition cycles if the condition for the malfunction is no longer present.

Diagnostic Aids
It may be necessary to check Testing for Intermittent Conditions and Poor Connections.

Test Description





The numbers below refer to the step numbers on the diagnostic table.
2. This step calibrates the BPP sensor.
3. This step checks to see if the DTC C0278 resets.
4. This step checks for poor connections at the BPP sensor harness connector.