Normal Operation

The Smart Junction Box (SJB) monitors the input from the instrument panel dimmer switch by sending a voltage reference signal through circuit VLN18 (BU/WH) to the instrument panel dimmer switch. The return signal is sent through circuit RLN29 (WH/OG) back to the SJB  . Based on the input from the instrument panel dimmer switch, the SJB  sends a Pulse Width Modulated (PWM) voltage to the dimmable illumination sources. If the SJB  detects a concern with the circuitry to the instrument panel dimmer switch, the SJB  defaults the backlighting to a full intensity level.

The SJB  also sends a message over the Controller Area Network (CAN) to the Front Controls Interface Module (FCIM) (vehicles without navigation), the Front Display Interface Module (FDIM) (vehicles without navigation), the HVAC module (vehicles with navigation), the Audio Control Module (ACM) (vehicles with navigation), the Rear Entertainment Module (RETM) (if equipped) and the Instrument Cluster (IC) to indicate the backlighting intensity level. If the receiving module receives invalid backlighting data from the SJB  for 5 seconds or less, the receiving module defaults the backlighting to the last setting.

If the receiving module does not receive the backlighting status message from the SJB  or if the data received is deemed invalid for more than 5 seconds, the receiving module sets DTC U0140 in continuous memory (except the HVAC module) and defaults the backlighting to full nighttime intensity.

• DTC B2212 (Panel Dim Switch Out Of Range) - an on-demand DTC that sets when the SJB  detects an open or short to voltage on the dimmer switch input circuit.

This pinpoint test is intended to diagnose the following: 

• Wiring, terminals or connectors
• Instrument panel dimmer switch
• SJB