Test N: DTC U0140 - Lost Communication With Body Control Module (GEM)

PINPOINT TEST N: DTC U0140 - LOST COMMUNICATION WITH BODY CONTROL MODULE (GEM)

Normal Operation
The audio control module (ACM) receives the following signals from the smart junction box (SJB) via the medium speed controller area network (MS-CAN):
- Ignition switch position
- Illumination
- Delayed accessory enable

Rather than use a battery feed through the ignition switch, the ignition switch position signal is used to "wake up" the audio system modules. If the SJB is not broadcasting the ignition switch position signal, none of the audio system modules will power-up, resulting in the audio system being completely inoperative.

The illumination signal is sent to multiple modules, including the front controls interface module (FCIM) and the front display interface module (FDIM). If the SJB is not broadcasting the illumination signal, the FDIM and FCIM will default to full nighttime brightness.

The delayed accessory function allows the audio system to be operated for a pre-determined amount of time after the key has been turned to OFF and a front door has not been opened. If the delayed accessory enable message is missing, the audio system defaults to the ignition switch position signal (delayed accessory disabled).

- DTC U0140 (Lost Communication With Body Control Module [GEM]) - sets when any of the above messages are missing for greater than 5 seconds.

This pinpoint test is intended to diagnose the following:
- Communication network concern
- SJB
- ACM

N1-N3: