P0556

DTC Troubleshooting: P0556

DTC P0556: Brake Booster Pressure Sensor Circuit Range/Performance Problem

Special Tools Required

- Vacuum pump/gauge, 0-30 in. Hg, Snap-on YA4000A or equivalent, commercially available
NOTE: If DTC P0556 is stored at the same time as DTC P0571, troubleshoot DTC P0571 first, then recheck for DTC P0556.

1. Turn the ignition switch to LOCK (0).

2. Disconnect the vacuum hose (A) for the brake booster pressure sensor (B) from the brake booster, and connect a vacuum pump/gauge, 0-30 in.Hg, to the brake booster pressure sensor hose.

3. Turn the ignition switch to ON (II).

4. Check the BRAKE BOOSTER PRESSURE SENSOR in the DATA LIST with the HDS before and after applying vacuum to the hose using the vacuum pump/gauge.

Does the indicated value change?
YES - Go to step 5.

NO - Replace the brake booster pressure sensor. Service and Repair






5. Turn the ignition switch to LOCK (0).

6. Check for vacuum leaks or clogging at these parts:
- Brake booster pressure sensor hose.

- Brake booster vacuum hoses and their joints.

- Check valve (intake manifold).

- Check valve (vacuum pump) and filter.

- Brake booster.

Are the parts OK?
YES - Go to step 7.

NO - Repair or replace the leaking or clogged part(s).


7. Check the brake pedal position switch signal circuit. Brake Pedal Position Switch Signal Circuit Troubleshooting

Is the circuit OK?
YES - Go to step 8.

NO - Troubleshoot the brake pedal position switch signal circuit.


8. Reconnect the vacuum hose on the brake booster pressure sensor to the brake booster.

9. Turn the ignition switch to ON (II).

10. Note the BRAKE BOOSTER PRESSURE in the DATA LIST with the HDS.

11. Turn the ignition switch to LOCK (0).

12. Do the battery terminal disconnection procedure, Procedures and wait several seconds.

13. Do the battery terminal reconnection procedure, Procedures then do this procedure after the troubleshooting.

14. Check the BRAKE BOOSTER PRESSURE SENSOR in the DATA LIST with the HDS when the electric vacuum pump runs while you turn the ignition switch to ON (II). Do not start the engine.

Does the indicated value change when the motor runs?
YES - Intermittent failure, the system is OK at this time. Check for loose terminals between the electric vacuum pump relay 2 4P connector, the electric vacuum pump 2P connector, the brake pedal position switch 4P connector, and PCM connector A (44P). Refer to intermittent failures troubleshooting. Initial Inspection and Diagnostic Overview

NO - If the pump does not run, go to step 15. If the pump runs, turn the ignition switch to LOCK (0), then repeat step 12 to 14 again. If you still get the same brake booster pressure sensor value, replace the electric vacuum pump.


15. Turn the ignition switch to LOCK (0).

16. Check the connection and pin fit of the electric vacuum pump 2P connector.

Is the connector properly connected?
YES - Go to step 17.

NO - Connect the electric vacuum pump 2P connector properly. If necessary, repair or replace the connector.


17. Remove electric vacuum pump relay 2, and check it. Testing and Inspection

Is the relay OK?
YES - Go to step 18.

NO - Replace electric vacuum pump relay 2.


18. Remove the No. 17 (15 A) fuse from the under-hood fuse/relay box.

19. Remove the No. 31 (7.5 A) fuse from the auxiliary under-hood fuse/relay box.

20. Check for continuity between electric vacuum pump relay 2 terminal No. 2 and No. 31 (7.5 A) fuse in the auxiliary under-hood fuse/relay box terminal No. 1.

Is there continuity?
YES - Go to step 21.

NO - Repair open in the wire between electric vacuum pump relay 2 and the No. 31 (7.5 A) fuse in the auxiliary under-hood fuse/relay box.






21. Remove electric vacuum pump relay 1.

22. Install the No. 17 (15 A) fuse in the under-hood fuse/relay box.

23. Connect the electric vacuum pump relay 2 connector terminals No. 1 and No. 2, and electric vacuum pump relay 1 connector terminals No. 1 and No. 2 with jumper wires.

Does the electric vacuum pump motor run?
YES - Check for loose terminals in the electric vacuum pump relay 2 4P connector, the electric vacuum pump 2P connector, the brake pedal position switch 4P connector, and PCM connector A (44P), then update the PCM if it does not have the latest software, or substitute a known-good PCM, then go to step 1 and recheck. If no DTCs are indicated, and the PCM was substituted, replace the original PCM. Service and Repair

NO - Go to step 24.






24. Disconnect the electric vacuum pump 2P connector.

25. Measure the voltage between body ground and electric vacuum pump 2P connector terminal No. 1.

Is there battery voltage?
YES - Go to step 26.

NO - Repair open in the wire between electric vacuum pump relay 2 and the electric vacuum pump.






26. Check for continuity between body ground and electric vacuum pump 2P connector terminal No. 2.

Is there continuity?
YES - Replace the electric vacuum pump.

NO - Repair open in the wire between the electric vacuum pump and body ground (G503).