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Home >> Mazda >> 2022 >> MX-5 Miata RF Club >> Repair and Diagnosis >> Accessories & Equipment >> Communication Devices >> On-Board Diagnostic - Electric Supply Unit (ESU) >> DTC B124A-11: DRL Circuit Malfunction [Electrical Supply Unit (ESU)] >> Diagnostic Procedure

Diagnostic Procedure

DTC B124A:11 (ELECTRICAL SUPPLY UNIT) 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 terminal. (See NEGATIVE BATTERY TERMINAL 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 
 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 
 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 
 Yes Repeat the inspection from Step 1.

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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