Diagnostic Instructions

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	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
5-Volt Reference	P0557	P0557	P0558	P0556
Brake Booster Vacuum Sensor Signal	P0557	P0557	P0558	P0556
Low Reference	--	P0557	--	P0556

Circuit/System Description

The brake booster pressure sensor measures the negative air pressure or vacuum reserve in the brake booster assembly. During engine running conditions, the brake booster pressure sensor signal circuit voltage varies, depending on the vacuum reserve internal to the brake booster.

Conditions for Running the DTC

P0556

Engine running at idle.

P0557 or P0558

Ignition ON.

Conditions for Setting the DTC

P0556

The ECM detects brake booster vacuum as being less than the intake manifold vacuum for more than 100 milliseconds.

P0557

The ECM detects less than 0.04 volts on the brake booster sensor signal circuit for more than 12.5 milliseconds.

P0558

The ECM detects greater than 4.89 volts on the brake booster sensor signal circuit for more than 12.5 milliseconds.

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 Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Brake Assist System Description and Operation

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the brake booster vacuum sensor.
2. Ignition OFF, wait 60 seconds, test for less than 5 ohms between the low reference circuit terminal 2 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 1 and the signal circuit terminal 3.

⇒	If less than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

⇒	If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.

5. Ignition OFF, disconnect the X2 harness connector at the ECM.
6. Ignition OFF, test for infinite resistance between the signal circuit terminal 29 and ground.

⇒	If not the specified value, test the signal circuit for a short to ground.

7. If all circuits test normal, test or replace the power brake booster vacuum sensor.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.