DTC C1378/44: Capacitor Communication Malfunction [03/2017 - 09/2018]: Procedure

1. Make sure that there is no looseness at the locking part and the connecting part of the connector.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *a	Front view of wire harness connector (to Brake Control Power Supply with Bracket Assembly)

2. Disconnect the X77 brake control power supply with bracket assembly connector.
3. Turn the engine switch on (IG).
4. Measure the voltage according to the value(s) in the table below.

   Standard Voltage

   Tester Connection	Condition	Specified Condition
   X77-3 (IG1) - Body ground	Engine switch on (IG)	11 to 14 V

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR (IG1 CIRCUIT) 

Result: 

OK 

See step  2

1. Turn the engine switch off.

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

   *a	Front view of wire harness connector (to Brake Control Power Supply with Bracket Assembly)

2. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   X77-8 (GND) - Body ground	Always	Below 1 Ω

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR (GND CIRCUIT) 

Result: 

OK 

See step  3

1. Make sure that there is no looseness at the locking part and the connecting part of the connectors.
2. Disconnect the A9 and A10 skid control ECU assembly connectors.
3. Measure the resistance according to the value(s) in the table below.

   Standard Resistance

   Tester Connection	Condition	Specified Condition
   A9-20 (ENA) - X77-2 (ENA)	Always	Below 1 Ω
   A9-20 (ENA) or X77-2 (ENA) - Body ground	Always	10 kΩ or higher
   A10-30 (FAIL) - X77-7 (FAIL)	Always	Below 1 Ω
   A10-30 (FAIL) or X77-7 (FAIL) - Body ground	Always	10 kΩ or higher

   Result

   Proceed to
   OK
   NG

Result: 

NG 

REPAIR OR REPLACE HARNESS OR CONNECTOR 

Result: 

OK 

See step  4

1. Reconnect the A9 and A10 skid control ECU assembly connectors.
2. Reconnect the X77 brake control power supply with bracket assembly connector.
3. Clear the DTCs.

   Refer to DTC CHECK / CLEAR [03/2017 - 09/2018]

   Chassis > ABS/VSC/TRAC > Clear DTCs 

4. Turn the engine switch off.
5. Turn the engine switch on (IG).
6. Check if the same DTC is output.

   Refer to DTC CHECK / CLEAR [03/2017 - 09/2018]

   Chassis > ABS/VSC/TRAC > Trouble Codes 

   Result

   Result	Proceed to
   DTC C1378/44 is output.	A
   DTC C1378/44 is not output.	B

Result: 

B 

USE SIMULATION METHOD TO CHECK. Refer to  HOW TO PROCEED WITH TROUBLESHOOTING [03/2017 - 04/2020] 

Result: 

A 

See step  5

1. Check the INF code from the Freeze Frame Data stored when DTC (C1378/44) was stored.

   Refer to FREEZE FRAME DATA [03/2017 - 05/2023]

   Result

   Result	Proceed to
   INF code 112 is output.	A
   INF code 112 is not output.	B

Result: 

A 

REPLACE BRAKE CONTROL POWER SUPPLY WITH BRACKET ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023] 

Result: 

B 

REPLACE SKID CONTROL ECU ASSEMBLY. Refer to  REMOVAL [03/2017 - 05/2023]