Automatic Lighting Control Unit

Control System DTCs

DTC Troubleshooting: U128D

DTC U128D : Automatic Lighting Control Unit Lost Communication With Gauge Control Module

1. Problem verification:

Problem verification
-1. Clear the DTCs with the HDS.

-2. Turn the ignition switch to LOCK (0) and then back to ON (II).

-3. Wait for at least 6 seconds.

-4. Check for DTCs with the HDS.

Is DTC U128D indicated?
-YES- Go to step 2.
-NO- Intermittent failure, the system is OK at this time. Check for loose or poor connections.

2. Determine possible failure area (gauge control module (tach) power and ground, B_CAN line):

Determine possible failure area (gauge control module (tach) power and ground, B_CAN line)
-1. Select B-CAN CONTROL UNITS INFORMATION from the BODY ELECTRICAL SYSTEM SELECT menu, and then select CHECK CONNECTED CONTROL UNITS.

-2. Check the DETECT/NOT AVAILABLE information of the GAUGE CONTROL MODULE.

Is DETECT indicated?
-YES- Go to step 7.
-NO- Go to step 3.

3. Fuse check:

Fuse check
-1. Check the following fuse.





Is the fuse OK?
-YES- Go to step 4.
-NO- Replace the fuse. If the fuse blows again, repair a short to ground in the No. A29 (10 A) fuse circuit.

4. Open wire check (+B_BACK_UP line):

Open wire check (+B_BACK_UP line)
-1. Turn the ignition switch to LOCK (0).

-2. Disconnect the following connector.





-3. Measure the voltage between test points 1 and 2.









Is there battery voltage?
-YES- Go to step 5.
-NO- Repair an open or high resistance in the wire.

5. Open wire check (GND line):

Open wire check (GND line)
-1. Check for continuity between test points 1 and 2 individually.














Is there continuity?
-YES- Go to step 6.
-NO- Repair an open or high resistance in the ground wire or poor ground (G502/G503).

6. Open wire check (B_CAN lines):

Open wire check (B_CAN lines)
-1. Disconnect the following connector.





-2. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- An open or poor connection in the B_CAN-L wire between the automatic lighting control unit and the gauge control module (tach).
-NO- An open or poor connection in the B_CAN-H wire between the automatic lighting control unit and the gauge control module (tach).

7. Open wire check (B_CAN lines):

Open wire check (B_CAN lines)
-1. Turn the ignition switch to LOCK (0).

-2. Disconnect the following connectors.





-3. Check for continuity between test points 1 and 2.









Is there continuity?
-YES- An open or poor connection in the B_CAN-L wire between the automatic lighting control unit and the gauge control module (tach).
-NO- An open or poor connection in the B_CAN-H wire between the automatic lighting control unit and the gauge control module (tach).