GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2004 🢒 GMC C Sierra - 2WD 🢒 Steering 🢒 Power Steering System 🢒 DTC C0870

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) connector. The signal must be digitized and differentiated within the powerpack controller 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 degree range.

The EHPS provides the BPP sensor with 5 volts (actual 4.3 volts) on the 5-volt reference circuit and a ground on the low reference circuit. Rotation of the BPP sensor during brake pedal movement provides the EHPS with a signal voltage from 1-4 volts through the BPP sensor signal circuit. When the control module detects that the BPP sensor signal or 5-volt reference voltage is outside the predetermined range, DTC C0870 is set.

Conditions for Running the DTC
    • EHPS module in RUN mode.
    • Ignition switch in ACC or ON position.
    • Battery voltage between 12-58 volts.

Conditions for Setting the DTC

BPP sensor supply voltage is greater than 5 volts or less than 0 volts (short or open circuit)

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 had brake pedal position.
    • Stores DTC C0870 in the powertrain control module (PCM).
    • History DTC C0870 will be set in PCM.

Conditions for Clearing the DTC
    • BPP sensor supply voltage returns within range.
    • 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 in Wiring Systems.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step checks the BPP sensor input voltage.

    2.

  2. This step checks for an open, short to B+ and short to ground in 5-volt reference circuit.

    3.

  3. This step tests for an open or short to ground in the BPP sensor 5-volt return circuit.

    4.

  4. This step test for an open or short to ground in the BPP sensor signal circuit.

    5.

  5. This step tests for a bad connection at the harness connector of the EHPS module.

Step

Action

Yes

No

Schematic Reference: Power Steering Schematics

Connector End Views Reference: Power Steering Connector End Views

1

Did you perform the electro-hydraulic power steering (EHPS) Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Power Steering System

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the brake pedal position (BPP) sensor Input Voltage parameter in the EHPS control module data list.

Is the voltage reading less than 0 volts or greater than 5 volts?

Go to Step 3

Go to Diagnostic Aids

3

Test the BPP sensor 5-volt reference circuit for one of the following conditions:

    • An open
    • A short to battery positive voltage
    • A short to ground

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 4

4

Test the BPP sensor 5-volt return circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 5

5

Test the BPP sensor signal circuit for an open or a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 6

6

Inspect for poor connections at the harness connector of the EHPS module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 8

Go to Step 7

7

Important: Always perform the calibration procedure for the BPP sensor. Refer to Brake Pedal Position Sensor Calibration Description and Operation .

Replace the EHPS powerpack. Refer to Power Steering Pump Replacement .

Did you complete the repair?

Go to Step 8

--

8

  1. Use the scan tool in order to clear the DTCs.
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK