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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 B1277-11: Back-Up Light Circuit Malfunction [Electrical Supply Unit (ESU)] >> Diagnostic Procedure

Diagnostic Procedure

DTC B1277:11 (ELECTRICAL SUPPLY UNIT) DIAGNOSTIC PROCEDURE

Step Inspection Action
1 VISUALLY INSPECT BACK-UP LIGHT BULB (LH) 
  • Visually inspect the back-up light bulb (LH).
  • Is the back-up light bulb (LH) normal?
 Yes Go to the next step.
No Replace the back-up light bulb (LH), then go to Step 7.
(See BACK-UP LIGHT BULB REMOVAL/INSTALLATION .)
2 VISUALLY INSPECT BACK-UP LIGHT BULB (RH) 
  • Visually inspect the back-up light bulb (RH).
  • Is the back-up light bulb (RH) normal?
 Yes Go to the next step.
No Replace the back-up light bulb (RH), then go to Step 7.
(See BACK-UP LIGHT BULB REMOVAL/INSTALLATION .)
3 INSPECT BACK-UP LIGHT (LH) CONNECTOR CONDITION 
  • Switch the ignition off.
  • Disconnect the negative battery terminal. (See NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
  • Disconnect the back-up light (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 7.
4 INSPECT BACK-UP LIGHT (RH) CONNECTOR CONDITION 
  • Disconnect the back-up light (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 7.
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 7.
6 INSPECT BACK-UP LIGHT CONTROL CIRCUIT FOR SHORT TO GROUND 
  • Verify that the back-up light (LH)/(RH) and electrical supply unit (ESU) connectors are disconnected.
  • Inspect for continuity between electrical supply unit (ESU) terminal 2Q (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 2Q-Back-up light (LH) terminal A
  • Electrical supply unit (ESU) terminal 2Q-Back-up light (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 the next step.
No Go to the next step.
7 VERIFY THAT REPAIRS HAVE BEEN COMPLETED 
 Yes Repeat the inspection from Step 1.

Go to the next step.
No Go to the next step.
8 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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