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Brake Booster Pump Motor Malfunction

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.

Diagnostic Fault Information

Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

Brake Booster Pump Motor B+

1

1

--

--

Brake Booster Pump Motor Ignition

1

1

1

--

Brake Booster Vacuum Switch Ignition

--

1

1

--

Brake Booster Pump Motor Control

1

1

2

--

Brake Booster Pump Motor Ground

--

1

1

--

1. Brake Booster Pump Motor Always Off

2. Brake Booster Pump Motor Always On

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

Connector End View Reference

Component Connector End Views

Description and Operation

Brake Booster Vacuum Assist 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 Verification

Verify that a vacuum leak is not present within the power brake booster system, refer to Brake Assist System Diagnosis .

Circuit/System Testing
  1. Ignition OFF, disconnect the harness connector at the M9 brake booster pump motor.
  2. Test for less than 10 Ω between the ground circuit terminal 1 and ground.
    3. ⇒If greater than the specified range, test the ground circuit for an open/high resistance.
  3. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 5 and ground.
    4. ⇒If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test or replace the M9 brake booster pump motor.
  4. 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.
  5. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 1 and ground.
    6. ⇒If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
  6. Verify that a test lamp does not illuminate between the control circuit terminal 2 and ground.
    7. ⇒If the test lamp illuminates, test the control circuit for a short to B+.
  7. Connect a 10 A fused jumper wire between the ignition circuit terminal 1 and the control circuit terminal 2, verify the M9 brake servo pump motor is activated.
    8. ⇒If the M9 brake booster pump motor is not active, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the M9 brake booster pump motor.
  8. If all circuits test normal, 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.
  2. Connect a 30 A fused jumper wire between the B+ terminal 5 and B+
  3. Connect a 7.5 A fused jumper wire between the ignition terminal 2 and B+
  4. Connect a jumper wire between the ground terminal 1 and ground, verify the M9 brake booster pump motor activates.
    5. ⇒If the M9 brake booster pump motor does not activate, replace the M9 brake booster pump motor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Servo Unit Pump Replacement

   


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