Pinpoint Test O: U0401

WARNING: This page is about a different variant/trim than selected.

Refer to MODULE COMMUNICATIONS NETWORK for schematic and connector information.

Normal Operation and Fault Conditions

The GSM and TCM communicate through messages sent over HS-CAN. The GSM will set a DTC if it receives an invalid or incomplete message from the TCM. Incomplete or corrupted messages typically result from high network traffic preventing the complete message from being received within the calibrated time limit.

DTC Fault Trigger Conditions

DTC	Description	Fault Trigger Condition
GSM U0401:00	Invalid Data Received from ECM/PCM A: No Sub Type Information	This DTC indicates the GSM is receiving messages from the TCM, but the TCM is reporting faults in key signals. This DTC could also set due to the transmission manual park override lever bolt being installed. This bolt is installed during manufacturing, but should be removed before installing the transmission into the vehicle.

Possible Sources

Manual park override lever bolt is installed
High network traffic event
Incorrect PMI
Connectors damaged or pushed-out terminals, corrosion, loose wires and missing or damaged seals
TCM fault

O1 VERIFY THE MANUAL PARK OVERRIDE BOLT HAS BEEN REMOVED FROM THE TRANSMISSION

NOTE: New transmissions may be equipped with a manual park override bolt that holds the transmission out of park. If this bolt is not removed, DTC U0401 may set in the GSM.
- If a new transmission was just installed, verify the manual park override bolt has been removed from the manual park release lever on the transmission. REFER to: Transmission Description - Overview .
Has the manual park override bolt been removed from the transmission?

Yes GO to O2

No Remove the manual park override bolt from the transmission.

O2 CHECK THE TCM (TRANSMISSION CONTROL MODULE) FOR DIAGNOSTIC TROUBLE CODES (DTCS)
- Using a diagnostic scan tool, CARRY OUT the TCM self-test.
Are any diagnostic trouble codes (DTCs) present in the TCM?

Yes RESOLVE those diagnostic trouble codes first. REFER to: DTC Chart and Pinpoint Tests .

No GO to O3

O3 CHECK THE GWM (GATEWAY MODULE A) FOR DIAGNOSTIC TROUBLE CODES (DTCS)
- Using a diagnostic scan tool, CARRY OUT the GWM self-test.
Are any diagnostic trouble codes (DTCs) present in the GWM?

Yes RESOLVE those diagnostic trouble codes first. REFER to: Communications Network .

No GO to O4

O4 ATTEMPT TO DUPLICATE THE DTC (DIAGNOSTIC TROUBLE CODE)

NOTE: If a GSM self-test is carried out, the driver door must be fully closed. A false P166B DTC may set if the driver door is not fully closed during the self-test.
- Using a diagnostic scan tool, clear all diagnostic trouble codes from the GSM.
- Road test the vehicle.
- Using a diagnostic scan tool, CARRY OUT the GSM self-test.
Is DTC U0401 present?

Yes GO to O5

No The system is operating correctly at this time. The concern may have been caused by a high network traffic event.

O5 CHECK FOR OTHER CAUSES OF COMMUNICATION CONCERNS

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 TCM or to the GSM. If recent service history is found:
  - verify correct replacement module was installed
    - HVBOM may be used to verify correct part application
  - 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
Were any causes of a communication concern found in the vehicle service history?

Yes PROGRAM or INSTALL a new module as necessary.

No GO to O6

O6 INSPECT ALL IN-LINE CAN (CONTROLLER AREA NETWORK) CONNECTORS
- Ignition OFF.
- Refer to MODULE COMMUNICATIONS NETWORK and TRANSMISSION CONTROLS - TR9070 for schematic and connector information. Disconnect all in-line CAN connectors between the GSM and the TCM.
- Using a good light source, inspect all disconnected electrical connectors for the following:
  - 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
  - spread terminals - install new terminals as necessary
Are any connector or pin issues present?

Yes REPAIR any connector or pin issues.

No GO to O7

O7 CHECK THE TCM (TRANSMISSION CONTROL MODULE) FOR CORRECT OPERATION

Ignition OFF.

Disconnect the TCM and all related in-line electrical connectors.

Using a good light source, inspect all disconnected electrical connectors for the following:
- corrosion - install new connector or terminal and clean the module pins
- damaged or bent pins - install new terminals or pins
- pushed-out pins - install new pins as necessary
- spread terminals - install new terminals as necessary

Reconnect the TCM and all other electrical connectors that were previously disconnected. Make sure they seat and latch correctly.

Operate the system and verify the concern is still present.

Is the concern still present?

Yes	CHECK OASIS for any applicable TSB. If a TSB exists for this concern, DISCONTINUE this test and FOLLOW TSB instructions. If no TSB addresses this concern, INSTALL a new TCM. REFER to: Transmission Control Module (TCM) .

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