Pinpoint Tests AQ: DTC U0121

Instrumentation, Message Center and Warning Chimes

Pinpoint Tests

Pinpoint Test AQ: DTC U0121

Normal Operation
- DTC U0121 (Lost Communication With Anti-Lock Brake System (ABS) Control Module) - sets in continuous memory DTC if data messages received from the ABS module over the High Speed Controller Area Network (HS-CAN) are missing for greater than 5 seconds.

This pinpoint test is intended to diagnose the following:

- ABS module
- Instrument Cluster (IC)



PINPOINT TEST AQ: DTC U0121

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AQ1 VERIFY THE CUSTOMER CONCERN


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

Yes
GO to AQ2.

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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AQ2 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 AQ3.

No
REFER to Information Bus.

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AQ3 RETRIEVE THE RECORDED DTCs FROM THE IC SELF-TEST


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

Yes
GO to Pinpoint Test AM (B1317) or GO to Pinpoint Test AN (B1318). Pinpoint Tests AM: DTC B1317 Pinpoint Tests AN: DTC B1318

No
GO to AQ4.

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AQ4 RECHECK THE IC DTCs


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

Yes
INSTALL a new ABS module. REFER to Antilock Brakes / Traction Control Systems. 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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