Pinpoint Test I: The Defrost System Does Not Shut Off Automatically
Glass, Frames and Mechanisms
Pinpoint Test I: The Defrost System Does Not Shut Off Automatically
Normal Operation
When the engine is running and the defrost switch (integral to the HVAC module or Front Controls Interface Module (FCIM) if equipped with navigation system) is pressed, the HVAC module activates the rear window defrost relay. For vehicles equipped with navigation system, the FCIM (Front Controls Interface Module) sends the defrost request message to the HVAC module over the Controller Area Network (CAN). When the rear window defrost relay is active, voltage is supplied to the rear window defrost grid. For vehicles equipped with a power sliding rear window, the rear window defrost grid does not activate unless the rear sliding window glass is in the fully CLOSED position due to a glass position switch in series with the grid circuit. The glass position switch is integral to the power sliding rear window assembly. There is a feedback circuit incorporated into the glass position switch which illuminates the rear window defrost switch LED when the defrost grid is active and the sliding glass is fully closed. If the sliding glass is opened while the defrost system is active, the heated mirrors continue to operate regardless of the rear window defrost switch LED status.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Rear window defrost relay
- HVAC module
PINPOINT TEST I : THE DEFROST SYSTEM WILL NOT SHUT OFF AUTOMATICALLY
NOTICE: Use the correct probe adapter(s) from the Flex Probe Kit when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
I1 CHECK REAR WINDOW DEFROST GRID POWER CIRCUIT FOR A SHORT TO VOLTAGE
- Disconnect: Rear Window Defrost Relay.
- Disconnect: Rear Window Defrost Grid Power (Passenger Side Terminal).
- Ignition ON.
- Measure the voltage between rear window defrost grid power terminal, harness side and ground.
Is the voltage greater than 10 volts?
Yes
REPAIR circuit CRD06 (BN/YE) for a short to voltage. TEST the system for normal operation.
No
If equipped with a power sliding rear window, GO to I2.
If not equipped with a power sliding rear window, GO to I4.
I2 CHECK THE REAR WINDOW DEFROST SWITCH LED STATUS
- Observe the rear window defrost switch status.
Is the rear window defrost switch LED illuminated?
Yes
GO to I3.
No
GO to I4.
I3 CHECK THE REAR WINDOW DEFROST FEEDBACK CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: Rear Window Defrost Grid Inline (passenger side) C3368.
- Disconnect: HVAC Module- Dual Automatic Temperature Control (DATC) C228A (With Navigation) or C2109A (Without Navigation) or HVAC Module- Electronic Manual Temperature Control (EMTC) C294A.
- Ignition ON.
- Measure the voltage between rear window defrost grid inline C3368-1, circuit CH122 (WH/OG), harness side and ground.
Is any voltage present?
Yes
REPAIR the circuit. TEST the system for normal operation.
No
GO to I6.
I4 CHECK THE HVAC MODULE
NOTICE: The following step uses a test light to simulate normal circuit loads. Use only the test light recommended in the Special Tools table at the beginning. To avoid connector terminal damage, use the Flex Probe Kit for the test light probe connection to the vehicle. Do not use the test light probe directly on any connector.
- Start the engine.
- Connect the 12-volt incandescent test light between rear window defrost relay socket pin 2, circuit CRD02 (BN/BU) and rear window defrost relay socket pin 1, circuit CBB54 (VT/OG).
Does the test light illuminate?
Yes
GO to I5.
No
INSTALL a new rear window defrost relay. TEST the system for normal operation.
I5 CHECK THE REAR WINDOW DEFROST RELAY CONTROL CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- Disconnect: HVAC Module- Dual Automatic Temperature Control (DATC) C228A (With Navigation) or C2109A (Without Navigation) or HVAC Module- Electronic Manual Temperature Control (EMTC) C294A.
- Measure the resistance between rear window defrost relay socket pin 2, circuit CRD02 (BN/BU), harness side and ground.
Is the resistance greater than 10,000 ohms?
Yes
GO to I6.
No
REPAIR short to ground in circuit CH122 (WH/OG). TEST the system for normal operation.
I6 CHECK FOR CORRECT HVAC MODULE OPERATION
- Disconnect all HVAC module connectors.
- Check for:
- corrosion.
- pushed-out pins.
- Connect all HVAC module connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
Is the concern still present?
Yes
INSTALL a new HVAC module. TEST the system for normal operation.
No
The system is operating correctly at this time. Concern may have been caused by a loose or corroded connector. TEST the system for normal operation.