• 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.

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.

Engine Running.

Ignition ON/Ignition ON/Vehicle in Service Mode.

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

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

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

DTCs P0556, P0557 or P0558 are Type B DTCs..

DTCs P0556, P0557 or P0558 are Type B DTCs.

Hydraulic Brake Schematics

Master Electrical Component List

Brake Assist System Description and Operation

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Control Module References for scan tool information

1. Verify that the brake booster vacuum system has no damage, leakage or incorrect installation.
• If damage, leakage or incorrect installation is found

  Refer to Brake System Vacuum Source Test.

• If the inspection is OK
2. 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.
3. 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.
• If less than 10 Ω
4. Ignition ON/Ignition ON/Vehicle in Service Mode.
5. 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.
• 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.
• If between 4.8–5.2 V
6. 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.
• If less than 1 V
7. Ignition OFF/Ignition OFF/Vehicle OFF, disconnect the harness connector at the K20 Engine Control Module.
8. 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.

• If infinite resistance
9. 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.

• If less than 2 Ω
10. Replace the B19B Brake Booster Vacuum Sensor.
11. 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.

• If the DTC does not set
12. All OK.

Perform the Diagnostic Repair Verification after completing the repair.

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