DTC Troubleshooting: U0121
DTC U0121: Gauge control module lost communication with ABS modulator-control unit
DTC Description
DTC
U0121 Gauge control module lost communication with ABS modulator-control unit
  

NOTE: If you are troubleshooting multiple DTCs, be sure to follow the instructions in B-CAN System Diagnosis Test Mode A.

NOTE: If you have any loss of communication DTCs for the PCM, troubleshoot those DTCs first.

1.
Problem verification:

Problem verification
?1.
Turn the vehicle to the ON mode.

?2.
Clear the DTCs with the HDS.


?3.
Turn the vehicle to the OFF (LOCK) mode and then the ON mode.

?4.
Wait for at least 6 seconds.

?5.
Check for DTCs with the HDS.
DTC Description
DTC
U0121 Gauge control module lost communication with ABS modulator-control unit
  

Is DTC U0121 indicated?

     
YES
     
     
     
Go to step 2.
     
NO
     
     
     
Intermittent failure, the system is OK at this time. Check for loose or poor connections.?
2.
Fuse check:

Fuse check
?1.
Check the following fuse.
Fuse
No. C27 (7.5 A)
Location
Under-dash fuse/relay box

Is the fuse OK?

     
YES
     
     
     
Go to step 3.
     
NO
     
     
     
Replace the fuse. If the fuse blows again, repair a short to ground in the No. C27 (7.5 A) fuse circuit.?
3.
Open wire check (IG1 VSA/ABS line):

Open wire check (IG1 VSA/ABS line)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Disconnect the following connector.
ABS modulator-control unit 38P connector

?3.
Turn the vehicle to the ON mode.

?4.
Measure the voltage between test points 1 and 2.
Test condition
Vehicle ON mode
ABS modulator-control unit 38P connector: disconnected
Test point 1
ABS modulator-control unit 38P connector No. 36
Test point 2
Body ground

Is there battery voltage?

     
YES
     
     
     
The IG1 VSA/ABS wire is OK. Go to step 4.
     
NO
     
     
     
Repair an open or high resistance in the wire.?
4.
Open wire check (GND lines):

Open wire check (GND lines)
?1.
Turn the vehicle to the OFF (LOCK) mode.

?2.
Check for continuity between test points 1 and 2 individually.
Test condition
Vehicle OFF mode
ABS modulator-control unit 38P connector: disconnected
Test point 1
ABS modulator-control unit 38P connector No. 1
Test point 2
Body ground

Test point 1
ABS modulator-control unit 38P connector No. 3
Test point 2
Body ground

Is there continuity?

     
YES
     
     
     
The GND wires are OK. Go to step 5.
     
NO
     
     
     
Repair an open or high resistance in the ground wire(s) or poor ground (G201).?
5.
Open wire check (F-CAN_H line):

Open wire check (F-CAN_H line)
?1.
Disconnect the following connector.
Gauge control module 32P connector

?2.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
ABS modulator-control unit 38P connector: disconnected
Gauge control module 32P connector: disconnected
Test point 1
ABS modulator-control unit 38P connector No. 38
Test point 2
Gauge control module 32P connector No. 21

Is there continuity?

     
YES
     
     
     
The F-CAN_H wire is OK. Go to step 6.
     
NO
     
     
     
An open or poor connection in the F-CAN_H wire.?
6.
Open wire check (B-CAN_L line):

Open wire check (B-CAN_L line)
?1.
Check for continuity between test points 1 and 2.
Test condition
Vehicle OFF (LOCK) mode
ABS modulator-control unit 38P connector: disconnected
Gauge control module 32P connector: disconnected
Test point 1
ABS modulator-control unit 38P connector No. 26
Test point 2
Gauge control module 32P connector No. 22

Is there continuity?

     
YES
     
     
     
The F-CAN_L wire is OK. Replace the gauge control module.?
     
NO
     
     
     
An open or poor connection in the F-CAN_L wire.?