Pinpoint Test I : The Defrost System Is Inoperative

WARNING: This page is about a different car, the 2016 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.

NOTE: 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 THE REAR WINDOW DEFROST GRID VOLTAGE

Disconnect: Rear Window Defrost Grid Power C402A.

Start the engine.

Activate the rear defrost switch and measure the voltage between rear window defrost grid power C402A-1 , circuit CRD06 (BN/YE) and ground.

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Is the voltage greater than 11 volts?

Yes	GO to I2.
No	GO to I3.

I2 CHECK THE REAR WINDOW DEFROST GRID GROUND

Ignition OFF.

Disconnect: Rear Window Defrost Grid Ground C402B.

Measure the resistance between rear window defrost grid ground C402B-1 , circuit GD150 (BK/WH) and ground.

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Is the resistance less than 3 ohms?

Yes	CARRY OUT the Grid Wire Test . REPAIR the rear window defrost grid or INSTALL a new liftgate glass. REFER to Window Grid Wire Repair . TEST the system for normal operation.
No	REPAIR the circuit. TEST the system for normal operation.

I3 CHECK THE POWER TO THE RELAY

Ignition OFF.

Disconnect: Rear Window Defrost Relay.

Ignition ON.

Measure the voltage between rear window defrost relay socket pin 1, circuit CBB52 (GN/WH), harness side and pin 3, circuit SBB51 (BU/RD), harness side and ground.

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Are the voltages greater than 11 volts?

Yes	GO to I4.
No	VERIFY Battery Junction Box(BJB) fuse 51 (40A) and fuse 52 (10A) are OK. If OK, REPAIR the affected circuit. TEST the system for normal operation.If not OK, REFER to the OEM Electrical Wiring Diagram Introduction to identify the possible causes of the circuit short. REPAIR the circuit. TEST the system for normal operation.

I4 CHECK THE HVAC MODULE OUTPUT

NOTE: 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 of this article. 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.

Activate the rear defrost switch.

Connect a 12-volt incandescent test light between rear window defrost relay socket pin 2, circuit CH122 (WH/OG) and rear window defrost relay socket pin 1, circuit CBB52 (GN/WH).

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Does the test light illuminate?

Yes	GO to I5.
No	GO to I6.

I5 CHECK THE REAR WINDOW DEFROST RELAY

Ignition OFF.

Carry out the rear window defrost relay component test.Refer to Component Testing for component testing.

Did the rear window defrost relay pass the component test?

Yes	REPAIR open in circuit CRD06 (BN/YE). TEST the system for normal operation.
No	INSTALL a new rear window defrost relay. TEST the system for normal operation.

I6 CHECK THE REAR DEFROST SWITCH STATUS (CC_RDEF) PID

Ignition OFF.

Ignition ON.

Using a diagnostic scan tool, view the HVAC module PIDs.

Monitor the HVAC module PID CC_RDEF while pressing and releasing the rear window defrost switch.

Does the PID agree with the rear window defrost switch status?

Yes

GO to I7.

If the climate control system is also inoperative or does not operate correctly, DIAGNOSE the climate control system. Climate Control System General Information and Diagnostics CLEAR the DTCs. TEST the system for normal operation.If the climate control system operates correctly except for the rear window defrost function, INSTALL a new FCIM. Refer to the appropriate Information and Entertainment Systems article for the procedure. CLEAR the DTCs. TEST the system for normal operation.

I7 CHECK CIRCUIT CH122 (WH/OG) FOR A SHORT TO VOLTAGE

Ignition OFF.

Disconnect: HVAC Module - EATC C228A or HVAC Module - EMTC C2357B.

Ignition ON.

Measure the voltage between rear window defrost relay socket pin 2, circuit CH122 (WH/OG), harness side and ground.

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Is any voltage present?

Yes	REPAIR the circuit. TEST the system for normal operation.
No	GO to I8.

I8 CHECK CIRCUIT CH122 (WH/OG) FOR AN OPEN

Ignition OFF.

If equipped with Electronic Manual Temperature Control(EMTC), measure the resistance between rear window defrost relay socket pin 2, circuit CH122 (WH/OG), harness side and C2357B-23 (HVAC module - Electronic Manual Temperature Control(EMTC)) circuit CH122 (WH/OG), harness side.

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If equipped with Electronic Automatic Temperature Control(EATC), measure the resistance between rear window defrost relay socket pin 2, circuit CH122 (WH/OG), harness side and C228A-25 (HVAC module - Electronic Automatic Temperature Control(EATC)), harness side.

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Is the resistance less than 3 ohms?

Yes	GO to I9.
No	REPAIR the circuit. TEST the system for normal operation.

I9 CHECK FOR CORRECT HVAC MODULE

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. Climate Control . 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.