Pinpoint Test T: The Brake Vacuum Pump is Inoperative
Anti-Lock Control
Pinpoint Test T: The Brake Vacuum Pump is Inoperative
Normal Operation
On vehicles equipped with a 3.5L engine, an electrically operated pump is used to supply additional vacuum to the brake booster. The ABS module controls the pump through a relay located in the Battery Junction Box (BJB). When activated, the relay supplies voltage to the brake vacuum pump. The ABS module uses a sensor mounted on the brake booster to monitor brake booster vacuum. The ABS module activates the pump when the vacuum in the brake booster is below 57.56 kPa (17 in-Hg) and deactivates the pump once the vacuum in the brake booster reaches a minimum of 71.11 kPa (21 in-Hg).
If the sensor on the brake booster suffers an internal failure, the vacuum pump can fail to operate (or it may operate continuously) and one or more DTCs is set in the ABS module. Altitude affects vacuum readings, subtract 3.3863 kPa (1 in-Hg) from the reading for every 304.8 m (1,000 ft) of elevation above sea level.
- DTC P258A (Brake Booster Vacuum Pump Relay Circuit Failure)- This DTC sets in continuous memory if the ABS module detects an open or high resistance in the relay control circuit.
- DTC P258B (Brake Booster Vacuum Pump Plausibility Failure)- This DTC sets in continuous memory if the ABS module detects that the desired vacuum level is not reached in a specified time in the brake booster when the brake vacuum pump is commanded on. This can be caused by a inoperative vacuum pump relay, an inoperative vacuum pump or an internal failure of the ABS module.
This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- Vacuum pump relay
- Brake booster vacuum sensor
- Brake vacuum pump
- ABS module
PINPOINT TEST T : THE BRAKE VACUUM PUMP IS INOPERATIVE
T1 CHECK THE DTCs FROM THE ABS MODULE SELF-TEST
- Review the DTCs retrieved and recorded during Inspection and Verification.
Are DTCs C109D, C109E and C109F present?
Yes
DIAGNOSE any vacuum sensor DTCs first, GO to Pinpoint Test I. Pinpoint Test I: DTCs C109D, C109E and C109F
No
GO to T2.
T2 CHECK THE BRAKE VACUUM PUMP RELAY
- Disconnect: Brake Vacuum Pump Relay.
- Connect the scan tool.
- Enter the following diagnostic mode on the scan tool: DataLogger- ABS Module.
- Install a known good relay in place of the brake vacuum pump relay.
- Toggle the vacuum pump (VAC_PMP) active command ON.
Does the brake vacuum pump run when commanded ON?
Yes
REMOVE the known good relay. INSTALL a new brake vacuum pump relay. CLEAR the DTCs. REPEAT the self-test.
No
REMOVE the known good relay. GO to T3.
T3 CHECK THE BRAKE VACUUM PUMP RELAY CONTROL CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition ON.
- Measure the voltage between the brake vacuum pump relay circuit CCB30 (GY/VT) and ground.
Is any voltage present?
Yes
REPAIR circuit CCB30 (GY/VT). CLEAR the DTCs. REPEAT the self-test.
No
GO to T4.
T4 CHECK THE BRAKE VACUUM PUMP RELAY CONTROL CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: ABS Module C135.
- Measure the resistance between ABS module C135-36, circuit CCB30 (GY/VT), harness side and brake vacuum pump relay circuit CCB30 (GY/VT).
Is the resistance less than 5 ohms?
Yes
GO to T5.
No
REPAIR circuit CCB30 (GY/VT). CLEAR the DTCs. REPEAT the self-test.
T5 CHECK THE BRAKE VACUUM PUMP RELAY OUTPUT CIRCUIT FOR AN OPEN
- Ignition OFF.
- Disconnect: Brake Vacuum Pump C1560.
- Measure the resistance between brake vacuum pump relay circuit CCB29 (WH/GN) and brake vacuum pump C1560-1, circuit CCB29 (WH/GN), harness side.
Is the resistance less than 5 ohms?
Yes
GO to T6.
No
REPAIR circuit CCB29 (WH/GN). CLEAR the DTCs. REPEAT the self-test.
T6 CHECK THE BRAKE VACUUM PUMP RELAY OUTPUT CIRCUIT FOR A SHORT TO GROUND
- Measure the resistance between the brake vacuum pump relay circuit CCB29 (WH/GN) and ground.
Is the resistance greater than 10,000 ohms?
Yes
GO to T7.
No
REPAIR circuit CCB29 (WH/GN). CLEAR the DTCs. REPEAT the self-test.
T7 CHECK THE BRAKE VACUUM PUMP GROUND CIRCUIT FOR AN OPEN
- Measure the resistance between the brake vacuum pump C1560-2, circuit GD123 (BK/GY), harness side and ground.
Is the resistance less than 5 ohms?
Yes
GO to T8.
No
REPAIR circuit GD123 (BK/GY). CLEAR the DTCs. REPEAT the self-test.
T8 CHECK THE VOLTAGE TO THE BRAKE VACUUM PUMP RELAY
- Ignition ON.
- Measure the voltage between the brake vacuum pump relay circuit CBB52 (GN/WH) and ground; and between the brake vacuum pump relay circuit SBB64 (VT/RD) and ground.
Are the voltages greater than 10 volts?
Yes
GO to T9.
No
VERIFY that BJB (Battery Junction Box) fuse 64 (40A) and fuse 52 (5A) are OK.
If OK, REPAIR circuit SBB64 (VT/RD) or CBB52 (GN/WH) for an open.
If not OK, REFER to the Wiring Diagrams to identify the possible causes of the circuit short [1][2]Diagrams By Number. CLEAR the DTCs. REPEAT the self-test.
T9 CHECK THE BRAKE VACUUM PUMP OPERATION
- Ignition OFF.
- Connect: Vacuum Pump C1560.
- Connect: BJB (Battery Junction Box) Fuse 64 (40A).
- Momentarily, connect a fused jumper wire between brake vacuum pump relay circuit SBB64 (VT/RD) and brake vacuum pump relay circuit CCB29 (WH/GN).
Does the vacuum pump run?
Yes
REMOVE the fused jumper wire. GO to T10.
No
REMOVE the fused jumper wire. INSTALL a brake new vacuum pump. CLEAR the DTCs and REPEAT the self-test.
T10 CHECK FOR CORRECT ABS MODULE OPERATION
- Check ABS module connector for:
- corrosion
- damaged pins
- pushed-out pins
- Connect: ABS Module.
- Connect: Vacuum Pump C1560.
- Connect: BJB (Battery Junction Box) Fuse 64 (40A).
- Connect: Brake Vacuum Pump Relay.
- Make sure each connector seats correctly, then operate the system and verify the concern is still present.
Is the concern still present?
Yes
INSTALL a new ABS module. REFER to Anti-Lock Brake System (ABS) Module . TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. CLEAR the DTCs. REPEAT the self-test.