Circuit Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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 k-5 k 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 can not be certain what BPP sensor signal voltage represents a brake pedal position at rest. The EHPS needs the zero reference to provide brake pedal position. The EHPS receives a control packet identifier (CPID) request from a scan tool to calibrate the zero reference position (learn home).

DTC C0278 can be set for the two 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 zero 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.