Code No. P0555: Brake Vacuum Sensor System <Vehicles with AS&G system>

OPERATION

A power voltage of 5 V is applied to the brake vacuum sensor power terminal (terminal No. 3) from the engine-ECU (terminal No. 127) and earthed to the engine-ECU (terminal No. 130) from the brake vacuum sensor (terminal No. 2).
The sensor signal is inputted to the engine-ECU (terminal No. 128) from the brake vacuum sensor output terminal (terminal No. 1).

FUNCTION

The brake vacuum sensor converts the vacuum pressure in the brake booster into a voltage signal and inputs the signal to the engine-ECU.
In response to the signal, the engine-ECU controls the AS&G system.

TROUBLE JUDGMENT

Check Condition

2 seconds later after the ignition switch has been in "ON" position or the engine has started up.

Judgment Criterion

The brake vacuum sensor output voltage is 4.5 V or more for 2 seconds.

The brake vacuum sensor output voltage is 0.2 V or less for 2 seconds.

PROBABLE CAUSES

Failed brake vacuum sensor
Open or shorted brake vacuum sensor circuit, harness damage, or connector damage

Failed engine-ECU

DIAGNOSIS PROCEDURE

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

Refer to Data List Reference Table .

Item No. 161: Brake vacuum 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. Connector check: A-38 brake vacuum sensor connector

Q. Is the check result normal?

Go to Step 3 .

Repair or replace the connector.

STEP 3. Perform voltage measurement at A-38 brake vacuum sensor connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal No. 3 and earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

Go to Step 7 .

Go to Step 4 .

STEP 4. Connector check: A-09 engine-ECU connector

Q. Is the check result normal?

Go to Step 5 .

Repair or replace the connector.

STEP 5. Check harness between A-38 (terminal No. 3) brake vacuum sensor connector and A-09 (terminal No. 127) engine-ECU connector.

Check power supply line for open/short circuit.

Q. Is the check result normal?

Go to Step 6 .

Repair the damaged harness wire.

STEP 6. M.U.T.-III data list

Refer to Data List Reference Table .

Item No. 161: Brake vacuum 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 then perform the variant coding (Refer to GROUP 00 - Precautions Before Service - How to Perform Variant Coding ).

STEP 7. Perform resistance measurement at A-38 brake vacuum sensor connector.

Disconnect connector, and measure at harness side.
Resistance between terminal No. 2 and earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 10 .

Go to Step 8 .

STEP 8. Connector check: A-09 engine-ECU connector

Q. Is the check result normal?

Go to Step 9 .

Repair or replace the connector.

STEP 9. Check harness between A-38 (terminal No. 2) brake vacuum sensor connector and A-09 (terminal No. 130) engine-ECU connector.

Check earthing line for open circuit and damage.

Q. Is the check result normal?

Go to Step 6 .

Repair the damaged harness wire.

STEP 10. Connector check: A-09 engine-ECU connector

Q. Is the check result normal?

Go to Step 11 .

Repair or replace the connector.

STEP 11. Check harness between A-38 (terminal No. 3) brake vacuum sensor connector and A-09 (terminal No. 127) engine-ECU connector.

Check power supply line for damage.

Q. Is the check result normal?

Go to Step 12 .

Repair the damaged harness wire.

STEP 12. Perform voltage measurement at A-38 brake vacuum sensor connector.

Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
Engine: Warming up, idle
Voltage between terminal No. 1 and earth.

OK: The voltage is reduced according to the brake depressing amount. (turn the ignition switch ON after the engine stops from the idling. Depress the brake pedal several times.)

Q. Is the check result normal?

Go to Step 14 .

Go to Step 13 .

STEP 13. Check harness between A-38 (terminal No. 1) brake vacuum sensor connector and A-09 (terminal No. 128) engine-ECU connector.

Check output line for short circuit.

Q. Is the check result normal?

Replace the brake vacuum sensor.

Repair the damaged harness wire.

STEP 14. Perform voltage measurement at A-09 engine-ECU connector.

Disconnect engine-ECU connector, and connect special tool power plant ECU check harness (MB991987), and then measure the voltage on the check connector.
Engine: Warming up, idle
Voltage between terminal No. 128 and earth.

OK: The voltage is reduced according to the brake depressing amount. (turn the ignition switch ON after the engine stops from the idling. Depress the brake pedal several times.)

Q. Is the check result normal?

Go to Step 6 .

Go to Step 15 .

STEP 15. Connector check: A-09 engine-ECU connector

Q. Is the check result normal?

Check output line for open circuit and damage.

Repair or replace the connector.