Pinpoint Test B: DTC U0121:87

Body Control Module (BCM)

Pinpoint Tests

Pinpoint Test B: DTC U0121:87

Normal Operation

- DTC U0121:87 (Lost Communication With Anti-Lock Brake System (ABS) Control Module: Missing Message) - sets in the BCM if data messages received from the ABS module 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:

- Communication network concern
- ABS module
- BCM

PINPOINT TEST B: DTC U0121:87

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B1 VERIFY THE CUSTOMER CONCERN

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

Yes
GO to B2.

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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B2 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 B3.

No
REFER to Module Communications Network Testing and Inspection, The ABS Module Does Not Respond To The Scan Tool.

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B3 RETRIEVE THE RECORDED DTCs FROM THE BCM AND SELF-TEST

- Check for recorded BCM DTCs from the self-test.
- Is DTC U3003:16 or DTC U3003:17 recorded?

Yes
For DTC U3003:16, GO to Pinpoint Test F. For DTC U3003:17, GO to Pinpoint Test G. Pinpoint Test F: DTC U3003:16 Pinpoint Test G: DTC U3003:17

No
GO to B4.

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B4 RECHECK THE BCM 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 BCM self-test.
- Is DTC U0121:87 still present?

Yes
GO to B5.

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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B5 CHECK FOR DTC U0121:87 SET IN OTHER MODULES

- Clear the DTCs.
- Ignition OFF.
- Ignition ON.
- Wait 10 seconds.
- Enter the following diagnostic mode on the scan tool: Self-Test.
- Retrieve the continuous memory DTCs from all modules.
- Is DTC U0121:87 set in any other module?

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

No
INSTALL a new BCM. REFER to Body Control Module (BCM) Service and Repair. TEST the system for normal operation.

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