C027B
DTC C027B
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.
DTC Descriptor
DTC C027B
- Brake Booster Electric Vacuum Pump
For symptom byte information refer to Symptom Byte List Symptom Byte List.
Diagnostic Fault Information
Circuit/System Description
The electronic brake control module monitors the control circuit of the brake booster pump relay. The electronic brake control module supplies ground through the pump relay control circuit which then supplies B+ voltage to actuate the brake booster pump. B+ voltage is supplied at all times to the coil side of the pump relay.
Conditions for Running the DTC
Ignition ON.
Conditions for Setting the DTC
The electronic brake control module detects a short to ground or a short to voltage on the control circuit.
Conditions for Clearing the DTC
The condition for setting the DTC is no longer present.
Reference Information
Schematic Reference
Hydraulic Brake Schematics Electrical Diagrams
Connector End View Reference
Component Connector End Views Sunshade - Left Front
Description and Operation
Brake Assist System Description and Operation Brake Assist System
Electrical Information Reference
* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs
Scan Tool Reference
Control Module References Control Module References for scan tool information
Circuit/System Verification
1. Ignition ON.
2. Verify the brake booster pump motor turns ON and OFF when commanding the brake booster electric vacuum pump ON and OFF with a scan tool.
• If the brake booster pump motor does not turn ON and OFF
Refer to Circuit/System Testing.
• If the brake booster pump motor turn ON and OFF
3. All OK.
Circuit/System Testing
1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the KR14 Brake Booster Pump Motor Relay. It may take up to 2 minutes for all vehicle systems to power down.
2. Connect a test lamp between the control circuit terminal 85 and B+, ignition ON.
3. 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 less than 1 V between the control circuit terminal 35 and ground.
• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V.
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.
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, replace the K17 Electronic Brake Control Module.
• If the test lamp turns ON and OFF
4. Ignition ON.
5. Verify that a test lamp illuminates between the B+ circuit terminals listed below and ground.
* Terminal 86
* Terminal 87
• 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, replace the KR14 Brake Booster Pump Motor Relay.
• If the test lamp illuminates
6. Replace the KR14 Brake Booster Pump Motor Relay.
7. 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
8. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)
* Control Module References Control Module References for Electronic Brake Control Module replacement, programming and setup.