Pinpoint Tests AN: DTC U0121

Instrumentation, Message Center and Warning Chimes

Pinpoint Tests

Pinpoint Test AN: DTC U0121

Normal Operation
- DTC U0121 (Lost Communication With Anti-Lock Brake System Control Module [ABS]) - sets in the Instrument Cluster (IC) if the data messages received from the ABS module over the High Speed Controller Area Network (HS-CAN) are missing.

This pinpoint test is intended to diagnose the following:

- ABS module
- IC


PINPOINT TEST AN: DTC U0121

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AN1 VERIFY CUSTOMER CONCERN


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

Yes
GO to AN2.

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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AN2 CHECK THE COMMUNICATION NETWORK


- 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 AN3.

No
REFER to Module Communications Network Testing and Inspection.

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AN3 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
For DTC B1317, GO to Pinpoint Test AK. Pinpoint Tests AK: DTC B1317

For DTC B1318, GO to Pinpoint Test AL. Pinpoint Tests AL: DTC B1318

No
GO to AN4.

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AN4 RECHECK THE IC 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 may not have been carried out.

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

Yes
INSTALL a new PCM. REFER to Electronic Engine Controls Service and Repair. TEST the system for normal operation. REPEAT the PCM self-test.

If DTC U0121 is still present, INSTALL a new IC module.

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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