Antilock Brake System

DTC C0870

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview) provides an overview of each diagnostic category.



DTC Descriptor
DTC C0870
- Device Voltage Reference Output 1 Circuit




Diagnostic Fault Information






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 ([1][2]Antilock Brakes / Traction Control Systems)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

ABS Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning) 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. Ignition OFF, 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.

• 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.

3. 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.

• 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.

4. With the DMM, verify the brake pressure sensor signal range is less than 4.4 volts.

• 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.

5. 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.

• 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.

6. 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.

• If not within the specified range or is erratic, replace the brake fluid pressure sensor.




Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Brake Fluid Pressure Sensor Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for BCM or EBCM replacement, setup, and programming