DTC U112B: Lost Communication With Electric Brake Booster(Local)

DTC detecting condition:

No : data is received from the electric brake booster.

Trouble symptom:

Cooperation control with the electric brake booster control module does not operate properly.

Wiring diagram:

Electric brake booster system Ref. to WIRING SYSTEM>ELECTRIC BRAKE BOOSTER SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Before performing diagnosis, refer to "CAUTION" in "General Description". Ref. to LAN SYSTEM (DIAGNOSTICS)>GENERAL DESCRIPTION>CAUTION .

CHECK CAN COMMUNICATION HARNESS .
Perform the basic diagnostic procedure to check for fault in CAN communication harness. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .

Was the basic diagnostic procedure performed up to step 7?

Yes : Go to 2.

No : Perform the basic diagnostic procedure. Ref. to LAN SYSTEM (DIAGNOSTICS)>BASIC DIAGNOSTIC PROCEDURE .
CHECK DTC (OTHER THAN U-CODE) .
Check the displayed DTC.

Is DTC other than U*** displayed? (Current code)

Yes : Perform the diagnosis for the displayed DTCs other than U-code.

No : Go to 3.
CHECK DTC .
Check the displayed DTC.

Is DTC U112B displayed? (Current code)

Yes : Go to 4.

No : Go to 9.
CHECK DTC .
1. Check CAN communication circuit. Ref. to LAN SYSTEM (DIAGNOSTICS)>CAN COMMUNICATION CIRCUIT CHECK .
2. Using the Subaru Select Monitor, read all DTCs. Ref. to LAN SYSTEM (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .
Is DTC U112B displayed? (Current code)

Yes : Go to 5.

No : Go to 9.
CHECK HARNESS (OPEN CIRCUIT) .
1. Turn the ignition switch to OFF.
2. Disconnect the connector from the electric brake booster control module.
3. Disconnect the connector from the VDC control module & H/U.
4. Using a tester, measure the resistance between the electric brake booster control module connector and VDC control module & H/U connector.
Connector & terminal

(B664) No. 25 - (B310) No. 11:

(B664) No. 16 - (B310) No. 25:

Is the resistance less than 10 Ω?

Yes : Go to 6.

No : Repair the open circuit of harness.
CHECK HARNESS (SHORT CIRCUIT TO POWER SUPPLY) .
1. Turn the ignition switch to ON.
2. Measure the resistance between the electric brake booster control module connector and chassis ground and between the VDC control module & H/U connector and chassis ground.
Connector & terminal

(B664) No. 25 (+) - Chassis ground (-):

(B664) No. 16 (+) - Chassis ground (-):

Is the voltage less than 1 V?

Yes : Go to 7.

No : Repair the short circuit to power supply in harness.
CHECK HARNESS (GROUND SHORT CIRCUIT) .
1. Turn the ignition switch to OFF.
2. Measure the resistance between the electric brake booster control module connector and chassis ground and between the VDC control module & H/U connector and chassis ground.
Connector & terminal

(B664) No. 25 - Chassis ground:

(B664) No. 16 - Chassis ground:

Is the resistance 1 MΩ or more?

Yes : Go to 8.

No : Repair the ground short circuit of harness.
CHECK DTC .
Using the Subaru Select Monitor, read DTC of all the systems. Ref. to LAN SYSTEM (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .

Is DTC U112B detected in several modules? (Current code)

Yes : Replace the electric brake booster control module. Ref. to BRAKE>BRAKE BOOSTER .

No : Replace the module that the DTC has been detected.
CHECK HARNESS .
1. Shake the harness, and check for poor contact.
2. Using the Subaru Select Monitor, read all DTCs. Ref. to LAN SYSTEM (DIAGNOSTICS)>DIAGNOSTIC TROUBLE CODE (DTC) .
Is DTC U112B displayed? (Current code)

Yes : Repair the poor contact of harness, or replace the harness.

No : Go to 10.
CHECK CONNECTOR .
Check the connector used for high speed CAN for poor contact.

Is there poor contact of connector?

Yes : Repair the connector that has poor contact, or replace harness.

No : It is possible that temporary poor communication occurs. Delete the DTC.