Diagnostic Instructions

DTC Descriptors

DTC P258A: Vacuum Pump Relay Control Circuit

DTC P258B: Vacuum Pump Performance

DTC P258C: Vacuum Pump Relay Control Circuit Low Voltage

DTC P258D: Vacuum Pump Relay Control Circuit High Voltage

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Relay Coil B+	P258A	P258A, P258C	--	P258B
Relay Coil Control	P258C	P258A	P258D	P258B
Brake Booster Pump Control	1	1	1	--
Brake Booster Pump Ground	1	1	--	--
1. Brake Booster Pump Malfunction

Circuit/System Description

The engine control module (ECM) monitors the control circuit of the brake booster pump relay. The ECM 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

P258A, P258C, P258D

Ignition ON.

P258B

Conditions for Setting the DTC

P258A, P258C

The ECM detects an open/high resistance on the relay coil control circuit.

P258B

The ECM detects an excessive difference in vacuum levels between the power brake booster and the manifold absolute pressure (MAP).

P258D

The ECM detects a short to voltage on the relay control circuit.

Action Taken When the DTC Sets

DTC P258A, P258B, P258C, P258D are Type B DTCs.

Conditions for Clearing the DTC

DTC P258A, P258B, P258C, P258D are Type B DTCs.

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

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

1. Verify that a vacuum leak is not present, refer to Brake System Vacuum Source Test
2. Ignition ON, command the relay ON and OFF with a scan tool. Observe to verify that the vacuum relay and motor turns ON and OFF with each command.

Circuit/System Testing

1. Ignition OFF, disconnect the vacuum pump relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Verify that a test lamp illuminates between the B+ circuit terminals listed below and ground.

•	Terminal 30

•	Terminal 86

⇒	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 relay.

4. Verify that a test lamp does not illuminate between the control circuit terminal 85 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

5. Disconnect the harness connector at the vacuum pump.
6. Test for less than 2 ohms between the vacuum pump ground circuit terminal 2 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

7. Connect the harness connector at the vacuum pump.
8. Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the vacuum pump is activated.

⇒	If the vacuum pump does not activate, test the control circuit for a short ground or an open/high resistance. If the circuit tests normal, test or replace the vacuum pump.

9. Ignition OFF, test for infinite resistance between the control circuit terminal 85 and ground.

⇒	If less than the specified value, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.

10. Disconnect the X1 harness connector at the ECM.
11. Test for less than 2 ohms between the control circuit terminal 85 at the relay cavity and terminal 18 at the ECM harness connector.

⇒	If greater than the specified range, test the control circuit for an open/high resistance.

12. If all circuits test normal, replace the brake booster pump relay. If the DTC resets, replace the power brake booster vacuum pump.

Component Testing

1. Ignition OFF, disconnect the vacuum pump relay.
2. Test for 60-180 ohms between terminals 85 and 86.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 85

•

30 and 87

•

30 and 86

•

86 and 87

⇒	If not the specified value, replace the relay.

4. Install a 30A fused jumper wire between relay terminal 86 and B+. Install a jumper wire between relay terminal 85 and ground.
5. Test for less than 2 ohms between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.