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Free to use workshop manual for your 2015+ Mk4 'ND' Mazda MX-5
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REAR WINDOW DEFOGGER SYSTEM INSPECTION

System wiring diagram

Inspection Procedure

Step

Inspection

Action

1
    VERIFY INSTRUMENT CLUSTER DTCs

  • Switch the ignition ON (engine off or on).

  • Perform the DTC inspection for the instrument cluster using the M-MDS.

    (See DTC INSPECTION [INSTRUMENT CLUSTER].)

  • Is a DTC displayed?

Yes

Repair the malfunctioning location according to the applicable DTC troubleshooting.

(See DTC TABLE [INSTRUMENT CLUSTER].)

No

Go to the next step.

2
    DETERMINE MALFUNCTIONING LOCATION BY PERFORMING PID/DATA MONITOR INSPECTION

  • Display the BCM PID [R_DEF_RLY] using the M-MDS.

    (See PID/DATA MONITOR INSPECTION [BCM].)

  • Turn the rear window defogger switch on.

  • Is the PID value on?

Yes

Go to Step 5.

No

Go to the next step.

3

Yes

Go to the next step.

No

Replace the climate control unit, then go to Step 10.

(See CLIMATE CONTROL UNIT REMOVAL/INSTALLATION [FULL-AUTO AIR CONDITIONER].)

(See CLIMATE CONTROL UNIT REMOVAL/INSTALLATION [MANUAL AIR CONDITIONER].)

4

Yes

NOTE:

  • The rear window defogger does not operate normally due to BCM control malfunction.

Replace the BCM, then go to Step 10.

(See BODY CONTROL MODULE (BCM) REMOVAL/INSTALLATION.)

No

Replace the climate control unit, then go to Step 10.

(See CLIMATE CONTROL UNIT REMOVAL/INSTALLATION [FULL-AUTO AIR CONDITIONER].)

(See CLIMATE CONTROL UNIT REMOVAL/INSTALLATION [MANUAL AIR CONDITIONER].)

5

Yes

Go to the next step.

No

Replace the rear window defogger relay, then go to Step 10.

(See RELAY LOCATION.)

6
    INSPECT REAR WINDOW DEFOGGER RELAY CIRCUIT FOR SHORT TO GROUND OR OPEN CIRCUIT

  • Verify that the rear window defogger relay is removed.

  • Connect the negative battery cable.

    (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.)

  • Measure the voltage at rear window defogger relay terminals C and E (vehicle wiring harness side).

  • Is the voltage B+?

Yes

Go to the next step.

No

Inspect the DEFOG 30 A fuse.

  • If the fuse is blown:

    • Refer to the wiring diagram and verify if there is a common connector between DEFOG 30 A fuse and rear window defogger relay terminals C and E.

        • If there is a common connector:

      • Inspect the common connector and terminals for corrosion, damage, or disconnection and the common wiring harnesses for short to ground to determine the malfunctioning location.

      • Repair or replace the malfunctioning location.

        If there is no common connector:

      • Repair or replace the wiring harness which is shorted to ground.

      • Replace the fuse.

  • If the fuse is damaged:

    • Replace the fuse.

  • If the fuse is normal:

    • Refer to the wiring diagram and verify if there is a common connector between positive battery terminal and rear window defogger relay terminals C and E.

        • If there is a common connector:

      • Inspect the common connector and terminals for corrosion, damage, or disconnection and the common wiring harnesses for an open circuit to determine the malfunctioning location.

      • Repair or replace the malfunctioning location.

        If there is no common connector:

      • Repair or replace the wiring harness which has an open circuit.

Go to Step 10.

7
    INSPECT REAR WINDOW DEFOGGER CIRCUIT FOR SHORT TO GROUND OR OPEN CIRCUIT

  • Install the rear window defogger relay.

  • Turn the rear window defogger switch on.

  • Measure the voltage at rear window defogger terminal 1A (vehicle wiring harness side).

  • Is the voltage B+?

Yes

Go to the next step.

No

Refer to the wiring diagram and verify if there is a common connector between rear window defogger relay terminals D and rear window defogger terminal 1A.

    If there is a common connector:

  • Inspect the common connector and terminals for corrosion, damage, or disconnection and the common wiring harnesses for short to ground or open circuit to determine the malfunctioning location.

  • Repair or replace the malfunctioning location.

    If there is no common connector:

  • Repair or replace the wiring harness which is shorted to ground or has an open circuit.

After repair procedure, go to Step 10.

8

Yes

Go to the next step.

No

Repair the rear window defogger, then go to Step 10.

(See REAR WINDOW DEFOGGER REPAIR.)

9
    INSPECT BCM CIRCUIT FOR SHORT TO GROUND OR OPEN CIRCUIT

  • Switch the ignition ON (engine off or on).

  • Measure the voltage at BCM terminal 3K (vehicle wiring harness side).

  • Is the voltage B+?

Yes

Replace the BCM, then go to the next step.

(See BODY CONTROL MODULE (BCM) REMOVAL/INSTALLATION.)

No

Refer to the wiring diagram and verify if there is a common connector between BCM terminal 3K and rear window defogger relay terminal A.

    If there is a common connector:

  • Inspect the common connector and terminals for corrosion, damage, or disconnection and the common wiring harnesses for short to ground or open circuit to determine the malfunctioning location.

  • Repair or replace the malfunctioning location.

    If there is no common connector:

  • Repair or replace the wiring harness which is shorted to ground or has an open circuit.

After repair, go to the next step.

10
    VERIFY IF MALFUNCTION IS RESOLVED

  • Does the rear window defogger system operate normally?

Yes

Explain the contents of the servicing to the customer.

No

If the malfunction has not been resolved, repeat the inspection from Step 1.
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Free to use workshop manual for your 2015+ Mk4 'ND' Mazda MX-5

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