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Computers/Controls - Erroneous DTC U1108

NUMBER: 08-003-05

GROUP: Electrical

DATE: January 26, 2005

SUBJECT:
Erroneous DTC U1108 May Occur If FCM Is Replaced On A TMC Equipped Vehicle

MODELS:

2005 (WH) Grand Cherokee (International Market Only)

NOTE:
This bulletin applies to vehicles equipped with Traffic Message Channel (sales code XRX) and a radio with an integrated display (sales code REJ).

DISCUSSION:

An erroneous Diagnostic Trouble Code (DTC) U1108 - "Additional CAN B ECU Detected" may be set if the Front Control Module (FCM) is replaced on a vehicle that is equipped with the Traffic Message Channel (TMC) feature. This condition may occur only if the replacement FCM part number is 56040662AJ.

The TMC module, the additional ECU detected on the CAN B bus, is not recognized by the "AJ" level software of a replacement FCM. Grand Cherokee vehicles originally assembled with an "AJ" level FCM and equipped with TMC should have this condition corrected during the vehicle assembly process and should not exhibit a U1108 DTC if the TMC module is present. Only the installation of an "AJ" level replacement FCM may cause this condition to occur.

DTC U1108 should be ignored on those vehicles that have a replacement FCM having part number 56040662AJ, and are equipped with the TMC feature.

A technician may not be able to determine if the FCM has been replaced. In those cases, if the technician needs to verify that the U1108 DTC in the FCM is caused by the presence of a TMC module, then the following steps can be performed:

1. Verify the current FCM part number and if vehicle is TMC equipped.

2. Turn ignition switch to the OFF position, disconnect the TMC module from the electrical harness. The TMC module is located in the right rear quarter panel.

3. Turn the ignition switch to the RUN position (engine not running) and determine if DTC U1108 is still an active fault in the FCM.

4. If DTC U1108 is no longer an active DTC in the FCM, then the presence of the TMC module on the CAN B bus is most probably the cause of this DTC. Reconnecting the TMC module should cause the U1108 DTC to again become an active FCM DTC.

POLICY:
Information Only

Disclaimer:
This bulletin is supplied as technical information only and is not an authorization for repair.
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