Chevrolet Trax: DTC C025E: Brake booster vacuum sensor/brake booster vacuum pump

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 C025E

Brake Booster Vacuum Sensor Circuit

DTC C027B

Brake Booster Electric Vacuum Pump

For symptom byte information refer to Symptom Byte List .

Diagnostic Fault Information

Circuit/System Description

The brake booster vacuum sensor measures the vacuum in the brake booster. The electronic brake control module supplies a 5 v reference and a low reference circuit to the brake booster vacuum sensor. The vacuum sensor supplies a voltage signal in relation to the pressure in the brake booster to the electronic brake control module. When the vacuum within the system becomes low, the electronic brake control module turns on the brake booster pump motor by providing battery voltage to the brake booster pump motor relay. The relay activates and supplies the voltage to the brake booster pump motor.

Conditions for Running the DTC

Engine running

Conditions for Setting the DTC

C025E 01

• A short to voltage is detected on the signal circuit.
• A short to voltage is detected on the 5 V reference circuit.
• A short to voltage is detected on the relay control circuit.

C025E 04

• A open/high resistance is detected on the vacuum sensor signal circuit.
• A open/high resistance is detected on the relay control circuit.

C025E 5A

The Electronic Brake Control Module detected an erratic Vacuum Sensor Signal that is not plausible.

C025E 71

The electronic brake control module receives an invalid serial data message from the engine control module.

C027B 01

The electronic brake control module receives an invalid serial data message from the engine control module.

C027B 04

The electronic brake control module receives an invalid serial data message from the engine control module.

Action Taken When the DTC Sets

• The ABS indicator turns ON.
• The red Brake warning indicator turns ON.
• The Electronic Brake Control Module disables the ABS, the traction control, and the electronic stability control for the duration of the ignition cycle.

Conditions for Clearing the DTC

• A current DTC clears when the diagnostic runs and passes.
• The history DTC will clear after 40 consecutive fault-free ignition cycles have occurred.

Reference Information

Schematic Reference

Hydraulic Brake Schematics (Encore), Hydraulic Brake Schematics (Trax)

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - ENCORE WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - TRAX

Description and Operation

Brake Assist System 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 Testing

C025E 71

1. Ignition ON.
2. Verify that no other DTCs are set.

If any other DTCs are set

Refer to Diagnostic Trouble Code (DTC) List - Vehicle .

If no other DTCs are set

3. Replace the K20 Engine Control Module.
4. Verify the DTC C025E does not set while operating the vehicle under the conditions for Running the DTC.

If the DTC sets

Replace the K17 Electronic Brake Control Module.

If the DTC does not set

5. All OK.

C025E 01, C025E 04, C025E 5A, C027B 01, or C027B 04

1. Ignition OFF and all vehicle systems OFF, disconnect the KR14 Brake Booster Pump Motor Relay. It may take up to 2 min for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal 1 (86) and ground.

If 10 ohms or greater

1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.

If less than 10 ohms

3. Ignition ON.
4. Verify a test lamp illuminates between the B+ circuit terminal 3 (30) and ground.

If the test lamp does not illuminate and the circuit fuse is good

1. Ignition OFF.
2. Test for less than 2 ohms in the B+ circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.

If the test lamp does not illuminate and the circuit fuse is open

1. Ignition OFF.
2. Test for infinite resistance between the B+ circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance

3. Test for infinite resistance between the control circuit terminal 5 (87) and ground.

• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the KR14 Brake Booster Pump Motor Relay.

If the test lamp illuminates

5. Connect a test lamp between the control circuit terminal 2 (85) and the ground circuit terminal 1 (86). Clear EBCM DTCs.
6. Verify the test lamp turns ON and OFF when commanding the Brake Booster Electric Vacuum Pump ON and OFF with a scan tool.

If the test lamp is always OFF

1. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
2. Test for infinite resistance between the control circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance

3. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K17 Electronic Brake Control Module.

If the test lamp is always ON

1. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module, ignition ON.
2. Test for less than 1 V between the control circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K17 Electronic Brake Control Module.

If the test lamp turns ON and OFF

7. Verify that a test lamp does not illuminate between the control circuit terminal 5 (87) and ground.

If the test lamp illuminates

Repair the short to voltage on the control circuit

If the test lamp does not illuminate

8. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the M9 Brake Booster Pump Motor. It may take up to 2 min for all vehicle systems to power down.
9. Test for less than 10 ohms between the M9 Brake Booster Pump Motor ground circuit terminal 2 and ground.

If 10 ohms or greater

1. Ignition OFF.
2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.

If less than 10 ohms

10. Connect the harness connector at the M9 Brake Booster Pump Motor.
11. Ignition ON, connect a 30 A fused jumper wire between the B+ circuit terminal 3 (30) and the control circuit terminal 5 (87) .
12. Verify the M9 Brake Booster Pump Motor is activated.

If the M9 Brake Booster Pump Motor does not activate

1. Ignition OFF, disconnect the harness connector at the M9 Brake Booster Pump Motor.
2. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the M9 Brake Booster Pump Motor.

If the M9 Brake Booster Pump Motor activates

13. Test for 60-180 ohms between terminals 85 and 86 on the relay.

If less than 60 or greater than 180 ohms

Replace the relay.

If between 60-180 ohms

14. Test for infinite resistance between the terminals listed below:

• 30 and 86
• 30 and 85
• 30 and 87
• 85 and 87

• If less than infinite resistance

Replace the relay.

If infinite resistance

15. Install a 20 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground.
16. Test for less than 2 ohms between terminals 30 and 87.

If 2 ohms or greater

Replace the relay.

If less than 2 ohms

17. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the B19B Brake Booster Vacuum Sensor. It may take up to 2 min for all vehicle systems to power down.
18. Test for less than 10 ohms between the low reference circuit terminal 2 and ground.

If 10 ohms or greater

1. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
2. Test for less than 2 ohms in the low reference circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K17 Electronic Brake Control Module.

If less than 10 ohms

19. Ignition ON.
20. Test for 4.8-5.2 V between the 5 V reference circuit terminal 3 and ground.

If less than 4.8 V

1. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module.
2. Test for infinite resistance between the 5 V reference circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance

3. Test for less than 2 ohms in the 5 V reference circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, replace the K17 Electronic Brake Control Module.

If greater than 5.2 V

1. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module, ignition ON.
2. Test for less than 1 V between the 5 V reference circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, replace the K17 Electronic Brake Control Module.

If between 4.8-5.2 V

21. Ignition OFF, disconnect the harness connector at the K17 Electronic Brake Control Module, Ignition ON.
22. Test for less than 1 V between the B19B Brake Booster Vacuum Sensor signal circuit terminal 1 and ground.

If greater than 1 V

Repair the short to voltage on the circuit.

If less than 1 V

23. Ignition OFF.
24. Test for infinite resistance between the B19B Brake Booster Vacuum Sensor signal circuit terminal 1 and ground.

If less than infinite resistance

Repair the short to ground on the circuit.

If infinite resistance

25. Test for less than 2 ohms in the B19B Brake Booster Vacuum Sensor signal circuit end to end.

If 2 ohms or greater

Repair the open/high resistance in the circuit.

If less than 2 ohms

26. Replace the B19B Brake Booster Vacuum Sensor.
27. Verify the DTC does not set while operating the vehicle under Conditions for Running the DTC.

If the DTC sets

Replace the K17 Electronic Brake Control Module.

If the DTC does not set

28. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• Power Brake Booster Vacuum Hose Replacement for brake booster vacuum sensor replacement
• Control Module References for control module replacement, programming and setup.

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