GM Service Manual Online
For 1990-2009 cars only

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 Descriptor

DTC C0870: Device Voltage Reference Output 1 Circuit

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Brake Pressure Sensor Signal

C0870

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C0870

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Brake Fluid Pressure Sensor 5-Volt Reference Circuit

C0870

C0870

C0870

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Brake Fluid Pressure Sensor Ground Circuit

--

C0870

--

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Circuit Description

The brake pressure sensor reference voltage is monitored for an over or under voltage condition.

Conditions for Running the DTC

    • The ignition is ON.
    • The vehicle speed is greater than 40 km/h (25 mph).

Conditions for Setting the DTC

A malfunction is detected if the supply voltage is above 5.6 volts or below 4.4 volts for more than 60 milliseconds.

Action Taken When the DTC Sets

    • A malfunction DTC is set.
    • The ABS, traction control system (TCS) and vehicle stability enhancement system (VSES) are disabled.
    • The ABS, SERVICE VEHICLE SOON and Stability Off lamp indicators are ON.

Conditions for Clearing the DTC

    • The condition for the DTC is no longer present.
    • A history DTC will clear after 100 consecutive ignition cycles if the condition for the malfunction is no longer present.
    • Using a scan tool.
    • The electronic brake control module (EBCM) automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles.

Diagnostic Aids

Possible causes of this DTC are the following conditions:

    • An open in the pressure sensor supply voltage circuit.
    • A short to ground in the pressure sensor supply voltage circuit.
    • A short to B+ in the pressure sensor supply voltage circuit.

Reference Information

Schematic Reference

Antilock Brake System Schematics

Connector End View Reference

Antilock Brake System 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 References for Scan Tool Information

Circuit/System Verification

Ignition ON, observe the scan tool

Circuit/System Testing

  1. Ignition OFF, disconnect the EBCM harness connector at the brake fluid pressure sensor.
  2. With a DMM test for less than 5.0 ohms of resistance between the brake fluid pressure sensor low reference circuit terminal 1 and ground.
  3. If greater than the specified range, with the DMM test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the EBCM.
  4. Ignition ON, with a DMM test for 4.4-5.6 volts between the brake fluid pressure sensor 5-volt reference circuit terminal 3 and ground.
  5. If less than the specified range, with the DMM test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.
    If greater than the specified range, with the DMM test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the EBCM.
  6. With the DMM, verify the brake pressure sensor signal range is less than 4.4 volts.
  7. If greater than the specified value, test the signal circuit terminal 2 for a short to voltage. If the circuit tests normal, replace the EBCM.
  8. Install a 3A fused jumper wire between the brake fluid pressure sensor signal circuit terminal 2 and the brake fluid pressure sensor 5-volt reference circuit terminal 3. With a DMM verify the voltage value is greater than 5.6 volts.
  9. If less than the specified value, test the signal circuit terminal 2 for a short to ground or an open/high resistance. If the circuit tests normal, replace the EBCM.
  10. If all circuits test normal, test or replace the brake fluid pressure sensor.

Component Testing

  1. Install a 3A fused jumper wire between the brake fluid pressure sensor 5-volt reference terminal 3 and 5 volts. Install a jumper wire between the low reference terminal 1 and ground.
  2. Sweep the sensor through the entire range while monitoring the resistance between the signal circuit terminal 2 and the low reference circuit terminal 1. The voltage should vary between 4.4-5.6 volts without any spikes or dropouts.
  3. If not within the specified range or is erratic, replace the brake fluid pressure sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

    •  Brake Pressure Modulator Valve Pressure Sensor Replacement
    •  Control Module References for BCM or EBCM replacement, setup, and programming