Pinpoint Test J: DTC U0121

Adaptive Headlighting

Pinpoint Test J: DTC U0121

Normal Operation

- DTC U0121 (Lost Communication With Anti-Lock Brake System (ABS) Control Module)- an on-demand DTC that sets when the Headlamp Control Module (HCM) does not receive braking informational messages from the ABS module for longer than 5 seconds.

This pinpoint test is intended to diagnose the following:

- Communication network concern

- ABS module

- Left headlamp assembly

PINPOINT TEST J : DTC U0121

J1 VERIFY THE CUSTOMER CONCERN

- Ignition ON.

- Verify that there is an observable symptom present.

Is an observable symptom present?

Yes
GO to J2.

No
The system is operating normally at this time. The DTC may have been set due to high network traffic or an intermittent fault condition.

J2 CHECK THE COMMUNICATION NETWORK

- Ignition ON.

- Enter the following diagnostic mode on the scan tool: Network Test.

- Carry out the network test.

Does the ABS module pass the network test?

Yes
GO to J3.

No
REFER to Information Bus, The ABS Module Does Not Respond To The Scan Tool Pinpoint Test B: The ABS Module Does Not Respond To The Scan Tool.

J3 CHECK FOR DTCs U3003:16 AND U3003:17 FROM THE ABS MODULE SELF-TEST

- Retrieve the continuous memory DTCs from the ABS module.

Is DTC U3003:16 or DTC U3003:17 recorded?

Yes
REFER to Antilock Brakes / Traction Control Systems.

No
GO to J4.

J4 RECHECK THE HCM (Headlamp Control Module) DTCs

NOTE: If new modules were installed prior to the DTC being set, the module configuration may be incorrectly set during Programmable Module Installation (PMI) or the PMI (Programmable Module Installation) may not have been carried out.

- Enter the following diagnostic mode on the scan tool: HCM (Headlamp Control Module) Self-Test.

- Clear the DTCs and repeat the HCM (Headlamp Control Module) self-test.

Is DTC U0121 still present?

Yes
GO to J5.

No
The system is operating correctly at this time. The DTC may have been set due to high network traffic or an intermittent fault condition.

J5 CHECK FOR DTC U0121:87 OR DTC U0121 SET IN OTHER MODULES

- Enter the following diagnostic mode on the scan tool: Self-Test.

- Retrieve the continuous memory DTCs from all modules.

Is DTC U0121:87 or DTC U0126 retrieved?

Yes
INSTALL a new ABS module. CLEAR the DTCs. REPEAT the HCM (Headlamp Control Module) self-test.

No
INSTALL a new left headlamp assembly. REFER to Headlamp Assembly . TEST the system for normal operation