Rear Window Defogger Malfunction
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Rear Window Defogger Malfunction
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Diagnostic Fault Information
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Circuit
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Short to Ground
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Open/High Resistance
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Short to Voltage
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Signal Performance
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Rear Window Defogger Relay Switch B+
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1
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1
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-
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-
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HVAC Control Serial Data
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U1510 00
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U1510 00
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U1510 00
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-
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Rear Window Defogger Relay Control
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B0283 02
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B0283 05
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B0283 05
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-
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Rear Defogger Grid Control
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1
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1
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2
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-
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Rear Window Defogger Relay Coil Ground
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-
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1
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1
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-
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Rear Defogger Grid Ground
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-
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1
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1
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-
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1. Rear Defogger Inoperative
2. Rear Defogger Always ON
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Circuit/System Description
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When the HVAC control module receives a rear window defog request from the HVAC control faceplate, the HVAC control module will supply voltage to the relay coil. Battery positive voltage is supplied at all times to the relay switched input and the relay coil is always grounded. This allows battery positive voltage from the relay switched input to flow through the switch contacts and out the relay switched output to the rear window defogger grid.
The rear window defogger indicator will still function when the rear defogger switch is pressed, but any of the following conditions may cause the rear window defogger grid not to function:
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The battery state of charge is out of range causing the HVAC control module to suspend the rear window defogger operation.
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The Remote Start Enable ambient temperature is greater than 5°C (40°F).
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Schematic Reference
Defogger Schematics
Connector End View Reference
Component Connector End Views
Description and Operation
Rear Window Defogger Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References
for scan tool information
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Circuit/System Verification
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1.
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Engine running, observe the scan tool Rear Defogger Switch parameter while pressing the heated rear window switch. The parameter should change from Inactive to Active.
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2.
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If the value does not change, replace the HVAC control.
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3.
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Observe the operation of the rear window defogger indicator while pressing the heated rear window switch. The indicator should turn ON or OFF each time the heated rear window switch is pressed.
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4.
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If the indicator does not turn ON or OFF with each switch press, replace the HVAC control.
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5.
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Command the Rear Defog ON and OFF with a scan tool. The rear defogger grid should turn ON and OFF when changing between the commanded states.
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1.
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Ignition OFF, disconnect the KR5 rear defogger relay.
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2.
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Test for less than 30 Ω between the ground circuit terminal 86 and ground.
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3.
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If greater than the specified range, test the ground circuit for an open/high resistance.
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4.
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Engine running, verify a test lamp does not illuminate between the control circuit terminal 87 and ground.
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5.
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If the test lamp illuminates, test the control circuit for a short to voltage.
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6.
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Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
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7.
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If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
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8.
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Ignition OFF, disconnect the X2 harness connector at the E18 rear defogger grid.
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9.
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Test for less than 30 Ω between the ground circuit terminal A and ground.
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10.
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If greater than the specified range, test the ground circuit for an open/high resistance.
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11.
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Connect the X2 harness connector at the E18 rear defogger grid.
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12.
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Engine running, connect a 40 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the E18 rear defogger grid is activated.
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13.
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If the rear defogger grid does not activate, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the E18 rear defogger grid.
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14.
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Connect a test lamp between the control circuit terminal 85 and the ground circuit terminal 86.
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15.
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Command the rear defogger grid ON and OFF by pressing and depressing the heated rear window switch, the test lamp should turn ON and OFF when changing between the commanded states.
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16.
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If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the K33 HVAC Control Module.
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17.
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If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K33 HVAC Control Module.
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18.
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If all circuits test normal, test or replace the KR5 rear defogger relay.
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Rear Window Defogger Grid Test
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1.
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Engine running, turn on the rear defogger grid.
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2.
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Verify that a test lamp illuminates between each rear window defogger grid line and ground. The test lamp should be off when testing at the ground side of the grid and get brighter as the test lamp moves closer to the voltage supply side of the grid. The test lamp should be dim when testing each grid line in the middle.
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3.
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If the test lamp remains bright at the middle of the grid line, test for an open between the test point and the ground side of the grid.
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4.
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If the test lamp remains off at the middle of the grid line, test for an open between the test point and the voltage supply side of the grid.
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Relay Test
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1.
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Ignition OFF, disconnect the KR5 rear defogger relay.
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2.
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Test for 60-180 Ω between terminals 85 and 86.
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3.
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If not within the specified range, replace the KR5 rear defogger relay.
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4.
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Test for infinite resistance between the following terminals:
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5.
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If not the specified value, replace the KR5 rear defogger relay.
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6.
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Install a 25A fused jumper wire between relay terminal 86 and 12V. Install a jumper wire between relay terminal 85 and ground. Test for less than 2 Ω between terminals 30 and 87.
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7.
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If greater than the specified range, replace the KR5 rear defogger relay.
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Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
