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. |
| • | Review Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P258A: Vacuum Pump Relay Control CircuitDTC 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 power brake booster vacuum sensor monitors the vacuum level in the brake booster. When the ECM detects the level has dropped too low, it commands the vacuum pump relay ON to activate the power brake booster vacuum pump to maintain the vacuum needed when the brakes are applied.
Conditions for Running the DTC
P258A, P258C, P258D
Ignition ON.
P258B
| • | Engine Running |
| • | Vacuum pump is activated for greater than 1.6 seconds. |
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 MIL/DTC
DTC P258A, P258B, P258C, P258D are Type B DTCs.
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Brake Assist System 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
Verify that a vacuum leak is not present, refer to Brake Assist System Diagnosis
Circuit/System Testing
- Ignition OFF, disconnect the vacuum pump relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.
- Verify that a test lamp illuminates between the B+ circuit terminal 30 and ground.
- Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
- Verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
- Disconnect the harness connector at the vacuum pump.
- Test for less than 2 ohms between the vacuum pump ground circuit terminal 2 and ground.
- Connect the harness connector at the vacuum pump.
- Connect a 20A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the vacuum pump is activated.
- Ignition OFF, test for infinite resistance between the control circuit terminal 86 and ground.
- Disconnect the X2 harness connector at the ECM.
- Test for less than 2 ohms between the control circuit terminal 86 at the relay cavity and terminal 20 at the ECM harness connector.
- If all circuits test normal, test or replace the power brake booster vacuum pump.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition circuit fuse is open, test or replace the relay. |
| ⇒ | 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 the control circuit terminal 85 for a short to ground. |
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | 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. |
| ⇒ | If less than the specified value, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
| ⇒ | If greater than the specified range, test the control circuit for an open/high resistance. |
Component Testing
- Ignition OFF, disconnect the vacuum pump relay.
- Test for 60-180 ohms between terminals 85 and 86.
- Test for infinite resistance between the following terminals:
- Install a 30A fused jumper wire between relay terminal 85 and B+. Install a jumper wire between relay terminal 86 and ground.
- Test for less than 2 ohms between terminals 30 and 87.
| ⇒ | If the resistance is not within the specified range, replace the relay. |
| • | 30 and 86 |
| • | 30 and 87 |
| • | 30 and 85 |
| • | 85 and 87 |
| ⇒ | If not the specified value, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
