Test B: The Control Illumination Is Inoperative

PINPOINT TEST B: THE CONTROL ILLUMINATION IS INOPERATIVE

B1-B2:

B2-B5:

B5-B7:

B7-B9:

B9-B12:

Normal Operation
The headlamp switch supplies the instrument cluster with the headlamp switch position status. The instrument panel dimmer switch provides the instrument cluster with the dimming control status through signal circuit 8-LE10 (WH/BK) and return circuit 9-LE10 (BN/YE). The instrument cluster sends the illumination message to the front electronic module (FEM) over the communication network, circuits 4-EG8 (GY/VT) and 5-EG8 (BU/WH), based upon the instrument panel dimmer switch position. The FEM is supplied with illumination voltage through circuit 29S-DK22 (OG/YE) whenever the switched system power (SSP) is energized. For additional information on the SSP operation, refer to Lighting and Horns. When the headlamp switch is in the PARK, HEADLAMP, or AUTOLAMP ON position, the instrument cluster sends the FEM an illumination message and the FEM, in turn, provides a pulse width modulation (PWM) voltage to the interior auxiliary junction box (AJB) through circuit 64S-LH2 (BU/RD) and then to the dimmable backlighting sources through circuits 64S-LK21 (BU/BK) and 64S-LK1 (LB). Circuit 64S-LK1 (LB) is then spliced and sent to the dimmable backlighting sub-sources through circuits 64-LK18 (BU/RD), 64S-LE10 (BU/YE), 64S-LH26 (BU/BK), 64S-LH45 (BU/OG), and 64S-LK29 (BU/RD). For the fixed backlighting system, when the ignition switch is in the ON position, the AJB sends the rear electronic module (REM) a voltage signal through circuit 29S-DK31 (OG/BK). The REM, in turn, sends B+ voltage to the fixed backlighting sources through circuit 7-LH1 (YE) for 100% illumination density.

Possible Causes
- circuit 7-LH1 (YE) open or short to ground
- circuit 8-LE10 (WH/BK) open or short to ground
- circuit 9-LE10 (BN/YE) open or short to ground
- circuit 64S-LE10 (BU/YE) open
- circuit 64S-LH2 (BU/RD) open or short to ground
- circuit 64S-LH26 (BU/BK) open or short to ground
- circuit 64S-LK1 (BU/RD) open or short to ground
- circuit 64S-LK29 (BU/RD) open or short to ground
- auxiliary junction box (AJB)
- front electronic module (FEM)
- rear electronic module (REM)
- instrument panel dimmer switch
- instrument cluster