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 Descriptors
DTC C0870 03: Device Voltage Reference Output 1 Circuit Voltage Below ThresholdDTC C0870 07: Device Voltage Reference Output 1 Circuit Voltage Above Threshold
Diagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
Brake Position Sensor 5-Volt Reference | C0870 03 | C0870 03 | C0870 07 | -- |
Stop Lamp Relay B+ | 1 | 1 | -- | -- |
Brake Position Sensor Signal | C0277 06 | C0277 06 | C0277 07 | C0277 09 |
Stop Lamp Switch Signal | P0572 | P0573 | P0573 | -- |
Stop Lamp Relay Control | 1 | 1 | 1 | -- |
Left Rear Stop/Turn Lamp Control | 1 | 1 | 1 | -- |
Right Rear Stop/Turn Lamp Control | 1 | 1 | 1 | -- |
Brake Position Sensor Low Reference | -- | C0277 06 | C0277 07 | -- |
Center High Mounted Stop Lamp (CHMSL) Ground | -- | 1 | 1 | -- |
Left Rear Stop/Turn Lamp Ground | -- | 1 | 1 | -- |
Right Rear Stop/Turn Lamp Ground | -- | 1 | 1 | -- |
1. Stop Lamps Malfunction | ||||
Circuit/System Description
The brake pedal position sensor is used to sense the action of the driver application of the brake pedal. The brake pedal position sensor provides an analog voltage signal that will increase as the brake pedal is applied. The body control module (BCM) provides a low reference signal and a 5-volt reference voltage to the brake pedal position sensor. When the variable signal reaches a voltage threshold indicating the brakes have been applied, the BCM will apply battery voltage to the stop lamps, transmission control module (TCM), engine control module (ECM), and stop lamp relay coil side. The BCM also supplies the stop lamp relay coil with ground. When the stop lamp relay receives battery voltage and ground from the BCM, the relay coil is energized and the stop lamp relay switch contacts close applying battery voltage through the STOP/B/U/LPS fuse to illuminate the center high mounted stop lamp (CHMSL).
Conditions for Running the DTC
Battery voltage must be between 9-16 volts.
Conditions for Setting the DTC
| • | DTC C0870 03 will set when the BCM detects a short to ground in the brake pedal position sensor voltage reference circuit for 0.5 seconds or greater. |
| • | DTC C0870 07 will set when the BCM detects a short to battery voltage in the brake pedal position sensor voltage reference circuits for 0.5 seconds or greater. |
Actions Taken When the DTC Sets
| • | The Service Vehicle Soon indicator is commanded ON. |
| • | If the DTC sets while the vehicle is running, the BCM will activate the brake lights when the vehicles transmission is not in the PARK position and the vehicle is not accelerating. |
Conditions for Clearing the DTC
| • | The condition responsible for setting the DTC no longer exists. |
| • | A history DTC will clear once 50 malfunction-free ignition cycles have occurred. |
| • | A DTC will not clear the current status until the next ignition cycle. |
Diagnostic Aids
Important: The stop lamps will not illuminate unless the ignition is in the ON position. For more detailed information concerning stop lamp operation, refer to Exterior Lighting Systems Description and Operation.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Exterior Lighting Systems Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the brake pedal position sensor.
- Ignition OFF, verify that a test lamp illuminates between B+ and the low reference circuit terminal A.
- Ignition ON, test for 4.8 -5.2 volts between the 5-volt reference circuit terminal C and ground.
- If all circuits test normal, test or replace the brake pedal position sensor.
| ⇒ | If the test lamp does not illuminate, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the BCM. |
| ⇒ | If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the BCM. |
| ⇒ | If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the BCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for BCM replacement, setup, and programming |
