Buick Regal: DTC P0556, P0557, or P0558

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.
• Refer to Diagnostic Procedure Instructions for an overview of each diagnostic category.

DTC Descriptors

DTC P0556

Brake Booster Pressure Sensor Performance

DTC P0557

Brake Booster Pressure Sensor Circuit Low Voltage

DTC P0558

Brake Booster Pressure Sensor Circuit High Voltage

Diagnostic Fault Information

Circuit/System Description

The brake booster vacuum sensor monitors the pressure in the brake booster. The engine control module supplies a 5 V reference and a low reference circuit to the brake booster vacuum sensor. The vacuum sensor supplies a voltage signal in relation to the pressure in the brake booster to the engine control module.

Conditions for Running the DTC

P0556

Engine Running.

P0557 or P0558

Ignition ON/Ignition ON/Vehicle in Service Mode.

Conditions for Setting the DTC

P0556

The engine control module detects brake booster vacuum as being less than the intake manifold vacuum for more than 100 ms.

P0557

The engine control module detects less than 0.01 V on the brake booster sensor signal circuit for more than 12.5 ms.

P0558

The engine control module detects greater than 4.9 V on the brake booster sensor signal circuit for more than 12.5 ms.

Action Taken When the DTC Sets

DTCs P0556, P0557 or P0558 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0556, P0557 or P0558 are Type B DTCs.

Reference Information

Schematic Reference

Hydraulic Brake Wiring Schematics

Connector End View Reference

Component Connector End View Index

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

DTC Type Reference

Refer to Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Refer to Control Module References for scan tool information

Circuit/System Testing

1. Ignition OFF/Ignition OFF/Vehicle OFF and all vehicle systems OFF, disconnect the harness connector at the B19B Brake Booster Vacuum Sensor. It may take up to 2 min for all vehicle systems to power down.

2. Test for less than 10 Ω between the low reference circuit terminal 2 and ground.

• If 10 Ω or greater

1. Disconnect the harness connector at the K20 Engine Control Module.
2. Test for less than 2 Ω in the low reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• Go to next step: If less than 10 Ω

3. Ignition ON/Ignition ON/Vehicle in Service Mode.

4. Test for 4.8 - 5.2 V between the 5 V reference circuit terminal 3 and ground.

• If less than 4.8 V

1. Ignition OFF/Ignition OFF/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module.
2. Test for infinite resistance between the 5 V reference circuit and ground.
   • If less than infinite resistance, repair the short to ground on the circuit.
   • Go to next step: If infinite resistance
3. Test for less than 2 Ω in the 5 V reference circuit end to end.
   • If 2 Ω or greater, repair the open/high resistance in the circuit.
   • If less than 2 Ω, replace the K20 Engine Control Module.

• If greater than 5.2 V

1. Ignition OFF/Ignition OFF/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the 5 V reference circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K20 Engine Control Module.

• Go to next step: If between 4.8 - 5.2 V

5. Test for less than 1 V between the B19B Brake Booster Vacuum Sensor signal circuit terminal 1 and ground.

• If greater than 1 V

1. Ignition OFF/Ignition OFF/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module, ignition ON.
2. Test for less than 1 V between the signal circuit and ground.
   • If 1 V or greater, repair the short to voltage on the circuit.
   • If less than 1 V, replace the K20 Engine Control Module.

• Go to next step: If less than 1 V

6. Ignition OFF/Ignition OFF/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module.

7. Test for infinite resistance between the B19B Brake Booster Vacuum Sensor signal circuit terminal 1 and ground.

• If less than infinite resistance

Repair the short to ground on the circuit.

• Go to next step: If infinite resistance

8. Test for less than 2 Ω in the B19B Brake Booster Vacuum Sensor signal circuit end to end.

• If 2 Ω or greater

Repair the open/high resistance in the circuit.

• Go to next step: If less than 2 Ω

9. Replace the B19B Brake Booster Vacuum Sensor.

10. Verify the DTC does not set while operating the vehicle under Conditions for Running the DTC.

• If the DTC sets

Replace the K20 Engine Control Module.

• Go to next step: If the DTC does not set

11. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

Refer to Control Module References for Engine Control Module replacement, programming and setup.

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