Pinpoint Test Q: DTC (Diagnostic Trouble Code) U0121:87

Refer to Module Communications Network for schematic and connector information.

Normal Operation and Fault Conditions

The IPMB communicates with the ABS module on the HS-CAN2.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Condition
IPMB U0121:87	Lost Communication With Anti-Lock Brake System (ABS) Control Module "A": Missing Message	Sets in continuous memory in the IPMB if expected messages from the ABS module are not received for 5 seconds or more when the ignition is on.

Possible Sources

Communication network concern
ABS module concern
IPMB concern

Q1 VERIFY THE CUSTOMER CONCERN

Ignition ON.

Verify whether an observable symptom is present.

Is an observable symptom present?

Yes

GO to Q2

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

Q2 CHECK THE COMMUNICATION NETWORK
- Using a diagnostic scan tool, perform the network test
Does the ABS module pass the network test?

Yes GO to Q3

No Refer to: Communications Network .

Q3 PERFORM THE ABS (ANTI-LOCK BRAKE SYSTEM) MODULE SELF-TEST

Using a diagnostic scan tool, perform the ABS module self-test.

Are any non-network Diagnostic Trouble Codes (DTCs) present?

Yes	DIAGNOSE all non-network Diagnostic Trouble Codes (DTCs). Refer to: Anti-Lock Brake System (ABS) and Stability Control .

GO to Q4

Q4 PERFORM THE IPMB (IMAGE PROCESSING MODULE B) SELF-TEST

Using a diagnostic scan tool, perform the IPMB self-test.

Are any non-network Diagnostic Trouble Codes (DTCs) present?

Yes	DIAGNOSE all non-network Diagnostic Trouble Codes (DTCs). Refer to the DTC Chart: IPMB .

GO to Q5

Q5 RECHECK THE IPMB (IMAGE PROCESSING MODULE B) DIAGNOSTIC TROUBLE CODES (DTCS)

Using a diagnostic scan tool, clear the IPMB Diagnostic Trouble Codes (DTCs).

Ignition OFF.

Ignition ON.

Wait 10 seconds.

Using a diagnostic scan tool, retrieve the IPMB Continuous Memory Diagnostic Trouble Codes (CMDTCs).

Is DTC U0121:87 still present?

Yes

GO to Q6

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.

Q6 CHECK FOR OTHER CAUSES OF COMMUNICATION NETWORK CONCERN

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

CHECK the vehicle service history for recent service actions related to the ABS module or IPMB if recent service history is found:
- verify correct replacement module was installed
  - vehicle parts build list may be used to verify correct part fitment
- verify the configuration of replacement module was correct
  - re-configure module using as-built data if prior configuration is suspect
- verify the module was not obtained from a like vehicle and installed into customer vehicle
  - return the swapped module to source vehicle and obtain new replacement module

Operate the system and determine if the observable symptom is still present.

Is the observable symptom still present?

Yes

GO to Q7

No	The system is operating correctly at this time. The concern may have been due to incorrect parts replacement procedures or incorrect module configuration.

Q7 CHECK FOR CORRECT ABS (ANTI-LOCK BRAKE SYSTEM) MODULE OPERATION

Ignition OFF.

Disconnect and inspect all ABS module and related in-line connectors.

Repair:
- corrosion (install new connector or terminals - clean module pins)
- damaged or bent pins - install new terminals/pins
- pushed-out pins - install new pins as necessary

Reconnect the ABS module and related in-line connectors. Make sure they seat and latch correctly.

Operate the system and determine if the concern is still present.

Is the concern still present?

Yes

CHECK OASIS for any applicable Technical Service Bulletins (TSBs). If a Technical Service Bulletin (TSB) exists for this concern, DISCONTINUE this test and FOLLOW the Technical Service Bulletin (TSB) instructions. If no Technical Service Bulletins (TSBs) address this concern, INSTALL a new ABS module. Refer to: Anti-Lock Brake System (ABS) Module .

No	The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. ADDRESS the root cause of any connector or pin issues.