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Home >> Ford >> 2009 >> Expedition RWD >> Repair and Diagnosis >> Electrical >> Gauges >> Instrument Cluster Illumination & Instrument Panel Illumination >> Diagnosis And Testing >> Instrument Cluster and Panel Illumination >> Pinpoint Tests >> Pinpoint Test D: All Instrument Panel Illumination Does Not Dim >> Normal Operation

Normal Operation

The Smart Junction Box (SJB) sends a voltage reference signal to the instrument panel dimmer switch through circuit CLN27 (WH/BN). The signal is routed through a variable resistor within the instrument panel dimmer switch and then back to the SJB  through circuit RLN29 (WH/OG) to an internal ground. The reference voltage changes depending on the position of the dimmer switch. When the dimmer switch is in the lowest setting, the resistance is low. When the SJB  senses the voltage is low (switch in the lowest setting), the dimmable backlighting intensity is low. When the SJB  senses the voltage reference is high (switch in the highest setting), the dimmable backlighting intensity is bright. The signal should be within a range (depending on the switch position) that the SJB  monitors. If the signal is too high (an open circuit or short to voltage), the SJB  faults the dimmable backlighting to full nighttime brightness. If circuit CLN27 (WH/BN) is short to ground, the SJB  interprets this as the lowest setting and sets the backlighting to the lowest intensity level, appearing to be inoperative.

The SJB  also sends a message over the network to the Audio Control Module (ACM), the Rear Entertainment Module (RETM), the HVAC module, and the Instrument Cluster (IC) to indicate the backlighting intensity level. If the receiving module receives no backlighting data or 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 intensity.

This pinpoint test is intended to diagnose the following: 

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