Pinpoint Test AK: PSCM (Power Steering Control Module) DTC (Diagnostic Trouble Code) U0121:00 Lost Communication With Anti-Lock Brake System (Abs) Control Module

NOTE: Refer to Steering GSB for additional connector and wiring inspection tips.

Refer to POWER STEERING CONTROLS for schematic and connector information.

Normal Operation and Fault Conditions

Description
The PSCM monitors the HS-CAN messages when the voltage to the PSCM is greater than 10 volts and there are no Diagnostic Trouble Codes (DTCs) present inhibiting PSCM operation.
For additional information on the messages sent to the PSCM from the ABS module, REFER to: Power Steering - System Operation and Component Description .

Pinpoint Test Applicability
This test applies to PSCM DTC U0121 Lost Communication with the ABS only. It does not apply to any other module except the PSCM.

DTC Diagnostic Strategy
If the module DTC list results in a large number of Diagnostic Trouble Codes (DTCs), diagnose all module hard faults first (C102D, C1B00, C200B, C200C, C200D, U2011 and U3000) before diagnosing any network faults (lost communication or invalid data). If voltage concern Diagnostic Trouble Codes (DTCs) are present, diagnose those after any module hard faults and before any network faults. Diagnose all current and active Diagnostic Trouble Codes (DTCs) before diagnosing any historic Diagnostic Trouble Codes (DTCs).

Pinpoint Test Purpose
To verify the PSCM wiring harness and connectors are OK. This test checks the connectors and wiring from the PSCM 3 pin connector at the steering gear to the in-line connector in the engine compartment. If these circuits are working correctly, the test then directs to check the ABS and wiring harness.

Diagnostic Aids
Do not install a new PSCM as part of the repair for a PSCM DTC U0121:00.
DTC U0121:00 indicates a possible failure of the HS-CAN which can be due to a circuit fault in the HS-CAN, the PSCM wiring harness or a ABS concern.
The presence of DTC U0121:00 may prevent the optional steering features; active park assist, Lane Keeping Assist (LKA) and Lane Centering Assist (LCA) from activating. If the DTC sets during an assist event, the event is terminated and the assist feature is deactivated.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Condition
PSCM U0121:00	Lost Communication With Anti-Lock Brake System (ABS) Control Module "A": No Sub Type Information	This DTC sets when the PSCM does not receive the ABS module messages within a certain time frame. This can occur if the ABS module wiring harness or electrical connectors are loose or damaged, or if the vehicle battery state of charge levels are low.

Possible Sources