Circuit 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 positive 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).
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC C0870 Device Voltage Reference Output 1 Circuit
DTC Symptom | DTC Symptom Descriptor |
|---|---|
03 | Voltage Below Threshold |
07 | Voltage Above Threshold |
Conditions for Running the DTC
Ignition voltage is within the normal operating voltage range.
Conditions for Setting the DTC
DTC C0870 03
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
The BCM detects a short to battery voltage in the brake pedal position sensor voltage reference circuits for 0.5 seconds or greater.
Action 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. |
| • | You issue a scan tool CLEAR DTCs command. |
| • | 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 .
Thoroughly inspect the wiring and connectors. An incomplete inspection of the wiring and connectors may result in misdiagnosis causing part replacement with the reappearance of the malfunction. If an intermittent malfunction exists, refer to Testing for Intermittent Conditions and Poor Connections .
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Exterior Lights Schematics Connector End View Reference: Master Electrical Component List | |||
1 | Did you perform the Diagnostic System Check - Vehicle? | Go to Step 2 | |
2 |
Does the scan tool display a change in the voltage? | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 |
3 | Is DTC C0870 03 present? | Go to Step 6 | Go to Step 4 |
4 |
Does the test light illuminate? | Go to Step 5 | Go to Step 10 |
5 | Test the brake pedal position sensor voltage reference circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 12 | Go to Step 7 |
6 | Test the brake pedal position sensor reference voltage circuit for an open or short to ground. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | Go to Step 12 | Go to Step 7 |
7 | Inspect for poor connections at the brake pedal position sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 12 | Go to Step 8 |
8 |
Important: Recalibrate the brake pedal position sensor after replacing. Refer to Brake Pedal Position Sensor Calibration . Replace the brake pedal position sensor. Refer to Brake Pedal Position Sensor Replacement . Did you complete the replacement? | Go to Step 9 | -- |
9 |
Does the scan tool display DTC C0870 as current? | Go to Step 10 | Go to Step 12 |
10 | Inspect for poor connections at the BCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | Go to Step 12 | Go to Step 11 |
11 | Replace the BCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | Go to Step 12 | -- |
12 |
Does the DTC reset? | Go to Step 2 | System OK |
