Pinpoint Test AM: DTC U0121

Instrumentation and Warning Chimes

Pinpoint Tests

Pinpoint Test AM: DTC U0121

Normal Operation
- DTC U0121 (Lost Communication With Anti-Lock Brake System (ABS) Control Module: No Sub-Type Information) - sets in the Instrument Cluster (IC) if data messages received from the ABS module over the High Speed Controller Area Network (HS-CAN) are missing. For a complete list of all network messages, refer to Module Communications Network Testing and Inspection.

This pinpoint test is intended to diagnose the following:

- ABS module
- IC

PINPOINT TEST AM: DTC U0121

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AM1 VERIFY THE CUSTOMER CONCERN

- Ignition ON.
- Verify that there is an observable symptom present.
- Is an observable symptom present?

Yes
GO to AM2.

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.

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AM2 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 AM3.

No
REFER to Module Communications Network Testing and Inspection.

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AM3 RETRIEVE THE RECORDED DTCs FROM THE SELF-TEST

- Check for recorded IC DTCs from the self-test.
- Is DTC B1317 or DTC B1318 recorded?

Yes
GO to Pinpoint Test AH (DTC B1317) or GO to Pinpoint Test AI (DTC B1318). Pinpoint Test AH: DTC B1317 Pinpoint Test AI: DTC B1318

No
GO to AM4.

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AM4 RECHECK THE IC DTCs

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

- Clear the DTCs. Repeat the IC self-test.
- Is DTC U0121 still present?

Yes
INSTALL a new ABS module. REFER to Vehicle Dynamic Systems Service and Repair. CLEAR the DTCs. REPEAT the IC self-test.

If DTC U0121 is still present, INSTALL a new IC. REFER to Instrument Cluster (IC) Instrument Cluster (IC). TEST the system for normal operation.

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.

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