Express 3500 V8-6.6L DSL Turbo (2008)
Heated Glass Element: Testing and Inspection
Rear Window Defogger Malfunction
Diagnostic Instructions
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Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. See: Testing and Inspection/Initial Inspection and
Diagnostic Overview/Diagnostic System Check - Vehicle
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Review Strategy Based Diagnosis for an overview of the diagnostic approach.
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Diagnostic Procedure Instructions provides an overview of each diagnostic category.
Diagnostic Fault Information
Circuit/System Description
When you depress the rear defogger button, voltage is supplied to the REAR DEFOG relay coil and the HVAC control assembly also illuminates the rear
window defogger indicator. Battery positive voltage is supplied at all times to the DEFOG relay switched input and the DEFOG relay coil is always
grounded. This allows battery positive voltage from the relay switched input through the switch contacts and out the relay switched output to the rear
window defogger grids. Ground for the rear defogger grids are provided by G401 or G402.
When you start the engine and press the rear defogger switch for the first time, the defogger cycle lasts for 15 minutes. Further operation results in 7.5
minute defogger cycles. The defogger cycle resets to 15 minutes when you cycle the ignition to the OFF position and then to the ON position.
Circuit/System Verification
1. Ignition ON, observe the operation of the rear window defogger grids while pressing and depressing the rear defog switch. The rear window
defogger grids should ACTIVATE and DEACTIVATE when changing between commanded states.
‹› If a single grid is inoperative, refer to Single Rear Window Defog Grid Inoperative.
‹› If both grids are inoperative, refer to Rear Window Defogger Inoperative.
2. Command the rear window defogger indicator ON and OFF by pressing and depressing the rear defog switch. The rear window defogger indicator
should turn ON and OFF when changing between the commanded states.
‹› If the defogger indicator continuously illuminates, replace the HVAC control assembly.
Circuit/System Testing
Single Rear Window Defog Grid Inoperative
1. Ignition OFF, disconnect the harness connector at the appropriate rear window defogger grid.
2. Test for less than 1 ohm between the rear window defogger grid ground circuit terminal listed below and ground.
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RPO A12 rear window defogger grid ground terminal A
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RPO A18 rear window defogger grid ground terminal B
‹› If greater than the specified range, test the ground circuit for an open/high resistance.
3. Ignition ON, connect a test light between the rear window defogger grid control circuit terminal A and ground.
