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DTC B124A:11 [ELECTRICAL SUPPLY UNIT (ESU)]

Description

DRL circuit malfunction

Detection condition

  • Electrical supply unit (ESU) detects a short to ground in the DRL circuit with the ignition switched ON (engine off or on).

Fail-safe

Not applicable

Possible cause

  • DRL bulb (LH) malfunction (bulb type)

  • DRL bulb (RH) malfunction (bulb type)

  • DRL (LH) connector or terminal malfunction

  • DRL (RH) connector or terminal malfunction

  • Electrical supply unit (ESU) connector or terminal malfunction

  • Short to ground in wiring harness between the following terminals:

    • Electrical supply unit (ESU) terminal 4J—DRL (LH) terminal A

    • Electrical supply unit (ESU) terminal 4J—DRL (RH) terminal A

  • DRL (LH) malfunction (LED type)

  • DRL (RH) malfunction (LED type)

  • Electrical supply unit (ESU) malfunction

Diagnostic Procedure

Step

Inspection

Action

1

VISUALLY INSPECT DRL BULB (LH)

NOTE:

  • For vehicles with DRL (LED type), go to Step 3.

  • Visually inspect the DRL bulb (LH).

  • Is the DRL bulb (LH) normal?

Yes

Go to the next step.

No

Replace the DRL bulb (LH), then go to Step 9.

(See DAYTIME RUNNING LIGHT (DRL) BULB REMOVAL/INSTALLATION.)

2

VISUALLY INSPECT DRL BULB (RH)
  • Visually inspect the DRL bulb (RH).

  • Is the DRL bulb (RH) normal?

Yes

Go to the next step.

No

Replace the DRL bulb (RH), then go to Step 9.

(See DAYTIME RUNNING LIGHT (DRL) BULB REMOVAL/INSTALLATION.)

3

INSPECT DRL (LH) CONNECTOR CONDITION
  • Switch the ignition off.

  • Disconnect the negative battery cable.

    (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.)

  • Disconnect the DRL (LH) connector.

  • Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection.

  • Is the connector normal?

Yes

Go to the next step.

No

Repair or replace the connector, then go to Step 9.

4

INSPECT DRL (RH) CONNECTOR CONDITION
  • Disconnect the DRL (RH) connector.

  • Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection.

  • Is the connector normal?

Yes

Go to the next step.

No

Repair or replace the connector, then go to Step 9.

5

INSPECT ELECTRICAL SUPPLY UNIT (ESU) CONNECTOR CONDITION
  • Disconnect the electrical supply unit (ESU) connector.

  • Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection.

  • Is the connector normal?

Yes

Go to the next step.

No

Repair or replace the connector, then go to Step 9.

6

INSPECT DRL CONTROL CIRCUIT FOR SHORT TO GROUND
  • Verify that the DRL (LH)/(RH) and electrical supply unit (ESU) connectors are disconnected.

  • Inspect for continuity between electrical supply unit (ESU) terminal 4J (wiring harness-side) and body ground.

  • Is there continuity?

Yes

Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals:

  • Electrical supply unit (ESU) terminal 4J—DRL (LH) terminal A

  • Electrical supply unit (ESU) terminal 4J—DRL (RH) terminal A

    If there is a common connector:
  • Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for a short to ground.

  • Repair or replace the malfunctioning part.

    If there is no common connector:
  • Repair or replace the wiring harness which has a short to ground.

Go to Step 9.

No

    Bulb type:
  • Go to Step 9.

    LED type:
  • Go to the next step.

7

VERIFY IF MALFUNCTIONING LOCATION IS DRL (LH) DEPENDING ON REPEATABILITY
  • Always reconnect all disconnected connectors.

  • Connect the negative battery cable.

    (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.)

  • Clear the DTC for the electrical supply unit (ESU) using the M-MDS.

    (See CLEARING DTC [ELECTRICAL SUPPLY UNIT (ESU)].)

  • Retrieve the electrical supply unit (ESU) DTCs using the M-MDS.

    (See DTC INSPECTION [ELECTRICAL SUPPLY UNIT (ESU)].)

  • Is the same DTC displayed?

Yes

Replace the DRL (LH), then go to the next step.

(See DAYTIME RUNNING LIGHT (DRL) REMOVAL/INSTALLATION.)

No

Go to Step 10.

8

VERIFY IF MALFUNCTIONING LOCATION IS DRL (RH) DEPENDING ON REPEATABILITY
  • Clear the DTC for the electrical supply unit (ESU) using the M-MDS.

    (See CLEARING DTC [ELECTRICAL SUPPLY UNIT (ESU)].)

  • Retrieve the electrical supply unit (ESU) DTCs using the M-MDS.

    (See DTC INSPECTION [ELECTRICAL SUPPLY UNIT (ESU)].)

  • Is the same DTC displayed?

Yes

Replace the DRL (RH), then go to the next step.

(See DAYTIME RUNNING LIGHT (DRL) REMOVAL/INSTALLATION.)

No

Go to Step 10.

9

VERIFY THAT REPAIRS HAVE BEEN COMPLETED
  • Always reconnect all disconnected connectors.

  • Connect the negative battery cable.

    (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.)

  • Clear the DTC for the electrical supply unit (ESU) using the M-MDS.

    (See CLEARING DTC [ELECTRICAL SUPPLY UNIT (ESU)].)

  • Retrieve the electrical supply unit (ESU) DTCs using the M-MDS.

    (See DTC INSPECTION [ELECTRICAL SUPPLY UNIT (ESU)].)

  • Is the same DTC displayed?

Yes

Repeat the inspection from Step 1.

  • If the malfunction recurs, replace the electrical supply unit (ESU).

    (See ELECTRICAL SUPPLY UNIT (ESU) REMOVAL/INSTALLATION.)

Go to the next step.

No

Go to the next step.

10

VERIFY IF OTHER DTCs DISPLAYED
  • Are any other DTCs displayed?

Yes

Repair or replace the malfunctioning part according to the applicable DTC troubleshooting.

(See DTC TABLE [ELECTRICAL SUPPLY UNIT (ESU)].)

No

DTC troubleshooting completed.

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Free to use workshop manual for your 2015+ Mk4 'ND' Mazda MX-5

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