For 1990-2009 cars

### Circuit Description

The brake booster pressure sensor measures the negative air pressure or vacuum reserve in the brake booster assembly. The engine control module (ECM) supplies the following circuits to the brake booster pressure sensor:

• | A 5-volt reference circuit

• | A signal circuit

• | A low reference circuit

During engine running conditions, the brake booster pressure sensor signal circuit voltage varies, depending on the vacuum reserve internal to the brake booster. If the ECM detects that the brake booster pressure sensor signal circuit is at a low voltage, then DTC P0557 sets.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0557 Brake Booster Pressure Sensor Circuit Low Voltage

### Conditions for Running the DTC

• | The ignition is ON.

• | The ignition voltage is greater than 11 volts, but less than 18 volts.

• | DTC P0557 runs continuously once the above conditions are met.

### Conditions for Setting the DTC

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

### Action Taken When the DTC Sets

• | The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails.

• | The control module records the operating conditions at the time the diagnostic fails. The control module stores the information in the Freeze Frame/Failure Records.

### Conditions for Clearing the MIL/DTC

• | The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• | A current DTC, last test failed, clears when the diagnostic runs and passes.

• | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• | Clear the MIL and the DTC with a scan tool.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step is measuring the current flow of the 5-volt reference circuit from the ECM.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views and Engine Controls Connector End Views
1 | Did you perform the Vehicle System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Observe the brake booster pressure sensor voltage parameter with a scan tool. Is the brake booster pressure sensor voltage parameter less than the specified value? | 0.2 V | Go to Step 4 | Go to Step 3
3 |

1. Observe the Freeze Frame/Failure Records for this DTC.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Is the brake booster pressure sensor voltage parameter less than the specified value?

0.2 V

Go to Step 4

Go to Testing for Intermittent Conditions and Poor Connections

4 | Is DTC P258A, B, C, or D also set? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Disconnect the brake booster pressure sensor wire harness electrical connector.
3. Test for shorted terminals and poor connections at the brake booster pressure sensor wire harness electrical connector and also the mating electrical connector on the brake booster pressure sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .

Did you find and correct the condition

--

Go to Step 15

Go to Step 6

6 |

1. Turn ON the ignition with the engine OFF.
2. Measure the voltage from the 5-volt reference circuit at the brake booster pressure sensor wire harness electrical connector to a good ground with a DMM. Refer to Circuit Testing .

Is the voltage within the specified range?

4.8-5.2 V

Go to Step 7

Go to Step 9

7 |

1. Turn OFF the ignition.
2. Connect one test lead of the DMM to the 5-volt reference circuit at the brake booster sensor wire harness electrical connector.
3. Connect the other test lead of the DMM to a good ground.
4. Configure the DMM to measure on the milliamps scale. Refer to Circuit Testing .
5. Turn ON the ignition with the engine OFF.

Is the amperage less than the specified value?

174 mA

Go to Step 9

Go to Step 8

8 |

1. Turn ON the ignition with the engine OFF.
2. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the brake booster pressure sensor, and the signal circuit of the brake booster pressure sensor.
3. Observe the brake booster pressure sensor voltage parameter with a scan tool.

Is the brake booster pressure sensor voltage parameter within the specified range?

4.8-5.2 V

Go to Step 13

Go to Step 10

9 | Test the brake booster pressure sensor 5-volt reference circuit for the following conditions:

• | An open

• | High resistance

• | A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

10 | Test the brake booster pressure sensor signal circuit for the following conditions:

• | An open

• | High resistance

• | A short to ground

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 11

11 | Test the brake booster pressure sensor low reference circuit for the following conditions:

• | An open

• | High resistance

Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 15

Go to Step 12

12 | Test for shorted terminals and poor connections at the engine control module (ECM) wire harness electrical connectors. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14
13 | Replace the brake booster pressure sensor. Did you complete the replacement? | -- | Go to Step 15 | --
14 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | --
15 |

1. Clear the DTCs with a scan tool.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Step 16

16 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle | System OK