Symptom Related Diagnostic Procedures
Brake Booster Pump Motor Malfunction
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.
Diagnostic Fault Information
Circuit/System Description
The brake booster vacuum switch monitors the amount of vacuum available to the power brake booster. When the vacuum within the system drops, the switch within the brake booster vacuum switch closes allowing voltage to be supplied to the brake booster pump motor.
Reference Information
Schematic Reference
Hydraulic Brake Schematics [1][2]Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
Description and Operation
Brake Booster Vacuum Assist Description and Operation Brake Booster Vacuum Assist
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. Verify that the brake booster vacuum system has no damage, leakage or incorrect installation.
• If damage, leakage or incorrect installation is found
Refer to Brake Assist System Diagnosis Component Tests and General Diagnostics.
• If the inspection is OK
2. All OK.
Circuit/System Testing
1. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the M9 Brake Booster Pump Motor. It may take up to 2 minutes for all vehicle systems to power down.
2. Test for less than 10 ohms between the ground circuit terminal 1 and ground.
• If 10 ohms or greater
1. 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 that a test lamp illuminates between the B+ circuit terminal 5 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, replace the M9 Brake Booster Pump Motor.
• If the test lamp illuminates
5. Ignition OFF, connect the harness connector at the M9 Brake Booster Pump Motor and disconnect the harness connector at the B19C Brake Booster Vacuum Switch, ignition ON.
6. Verify that a test lamp illuminates between the ignition circuit terminal 1 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 ignition 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 ignition circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, replace the B19C Brake Booster Vacuum Switch.
• If the test lamp illuminates
7. Verify that a test lamp does not illuminate between the control circuit terminal 2 and ground.
• If the test lamp illuminates
Repair the short to voltage on the control circuit.
• If the test lamp does not illuminate
8. Connect a 10 A fused jumper wire between the ignition circuit terminal 1 and the control circuit terminal 2.
9. Verify the M9 Brake Booster Pump Motor activates.
• If the brake booster pump motor does not activate
1. Ignition OFF, disconnect the harness connector at the M9 Brake Booster Pump Motor.
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 M9 Brake Booster Pump Motor.
• If the brake booster pump motor activates
10. Test or replace the B19C Brake Booster Vacuum Switch.
Component Testing
1. Ignition OFF, disconnect the harness connector at the M9 Brake Booster Pump Motor. Install a 30 A fused jumper wire between the B+ circuit terminal 5 and B+. Install a 7.5 A fused jumper wire between the ignition circuit terminal 2 and B+. Install a jumper wire between the ground circuit terminal 1 and ground.
2. Verify the M9 Brake Booster Pump Motor activates.
• If the brake booster pump motor does not activate
Replace the M9 Brake Booster Pump Motor.
• If the brake booster pump motor activates
3. All OK.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the repair.
Power Brake Booster Pump Replacement Service and Repair