Code No. P0557: Brake Booster Pressure Sensor Circuit Low Input

OPERATION

A power voltage of 5 V is applied to the brake booster pressure sensor connector power terminal from the engine-ECU connector terminal ACP5&BVS5 and earthed to the engine-ECU connector terminal ACPE&BVSE from the brake booster pressure sensor connector earth terminal.
The sensor signal is inputted to the engine-ECU connector terminal BVS from the brake booster pressure sensor connector output terminal.

FUNCTION

The brake booster pressure sensor detects a change in brake booster negative pressure and inputs the signal to the engine-ECU.

TROUBLE JUDGEMENT

Check Conditions

After 2 seconds since the ignition switch is turned ON or since the completion of engine start.
Battery positive voltage is more than 10 V and is less than 16.5 V.

Judgement Criterion

Senor output voltage is 0.3 V or less for two seconds (corresponding to 13 kPa or less of the brake booster pressure).

PROBABLE CAUSES

Failed brake booster pressure sensor
Open/short circuit or harness damage in brake booster pressure sensor circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

Refer to Data List Reference Table .

Item 171: Brake booster pressure sensor

Q. Is the check result normal?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

	Go to Step 2.

STEP 2. Perform voltage measurement at brake booster pressure sensor connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal ACP5&BVS5 line and earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 6.

	Go to Step 3.

STEP 3. Perform voltage measurement at engine-ECU connector

Measure engine-ECU terminal voltage.
Disconnect brake booster pressure sensor connector.
Ignition switch: ON
Voltage between terminal ACP5&BVS5 and earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector(s), or check and repair the harness of open circuit in ACP5&BVS5 line between brake booster pressure sensor connector and engine-ECU connector.

STEP 4. Check of short to earth between brake booster pressure sensor connector and engine-ECU connector.

Q. Is the check result normal?

	Go to Step 5.

	Repair the connector(s) or wiring harness.

STEP 5. M.U.T.-III data list

Refer to Data List Reference Table .

Item 171: Brake booster pressure sensor

Q. Is the check result normal?

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).

	Replace the engine-ECU.

STEP 6. Perform voltage measurement at brake booster pressure sensor connector.

Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness.
Ignition switch: ON
Voltage between terminal ACP5&BVS5 line and earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 7.

	Repair or replace the connector(s), or check and repair the harness of damage in ACP5&BVS5 line between brake booster pressure sensor connector and engine-ECU connector.

STEP 7. Perform voltage measurement at brake booster pressure sensor connector.

Use special tool test harness (MB991348) to connect connector, and measure at pick-up harness.
Start up the engine and let it idle for several minutes.
Stop the engine, and turn the ignition switch to the ON position.
Depress the brake pedal several times.
Voltage between terminal BVS line and earth.

OK: The more frequently the brake pedal is depressed, the more the voltage is decreased.

Q. Is the check result normal?

	Go to Step 9.

	Go to Step 8.

STEP 8. Check of short to earth in BVS line between brake booster pressure sensor connector and engine-ECU connector.

Q. Is the check result normal?

	Replace the brake booster pressure sensor.

	Repair the connector(s) or wiring harness.

STEP 9. Perform voltage measurement at engine-ECU connector

Measure engine-ECU terminal voltage.
Start up the engine and let it idle for several minutes.
Stop the engine, and turn the ignition switch to the ON position.
Depress the brake pedal several times.
Voltage between terminal code BVS and earth.

OK: The more frequently the brake pedal is depressed, the more the voltage is decreased.

Q. Is the check result normal?

	Go to Step 5.

	Repair or replace the connector(s), or check and repair the harness of open circuit, and damage in BVS line between brake booster pressure sensor connector and engine-ECU connector.