Pinpoint Tests AG: DTC U0121

Instrumentation, Message Center and Warning Chimes

Pinpoint Tests

Pinpoint Test AG: DTC U0121

Normal Operation
- DTC U0121 (Lost Communication With Anti-Lock Brake System Control Module (ABS)) - 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.

This pinpoint test is intended to diagnose the following:

- Module communication
- ABS module



PINPOINT TEST AG: DTC U0121

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AG1 VERIFY CUSTOMER CONCERN


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

Yes
GO to AG2.

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

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AG2 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 AG3.

No
REFER to Information Bus.

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AG3 RETRIEVE THE RECORDED DTCs FROM THE IC SELF-TEST


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

Yes
For DTC B1317, Go To Pinpoint Test AB. Pinpoint Tests AB: DTC B1317

For DTC B1318, Go To Pinpoint Test AC. Pinpoint Tests AC: DTC B1318

No
GO to AG4.

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AG4 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. 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.

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