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

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DTC B1313:12 [ELECTRICAL SUPPLY UNIT (ESU)]

Description	Map light circuit malfunction
Detection condition	Electrical supply unit (ESU) detects a short to power supply in the map light circuit.
Fail-safe	Not applicable
Possible cause	Map light malfunction Map light bulb malfunction Map light malfunction Map light connector or terminal malfunction Electrical supply unit (ESU) connector or terminal malfunction Short to power supply in wiring harness between map light terminal B and electrical supply unit (ESU) terminal 2L Electrical supply unit (ESU) malfunction

Diagnostic Procedure

Step	Inspection		Action
1	INSPECT MAP LIGHT Inspect the map light. (See MAP LIGHT INSPECTION.) Is the map light normal?	Yes	Go to the next step.
		No	Replace the map light bulb or map light, then go to Step 5. (See MAP LIGHT BULB REMOVAL/INSTALLATION.) (See MAP LIGHT REMOVAL/INSTALLATION.)
2	INSPECT MAP LIGHT CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the map light 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 5.
3	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 5.
4	INSPECT MAP LIGHT CIRCUIT FOR SHORT TO POWER SUPPLY Verify that the map light and electrical supply unit (ESU) connectors are disconnected. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Switch the ignition ON (engine off or on). Measure the voltage at map light terminal B (wiring harness-side). Is the voltage 0 V?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify whether or not there is a common connector between map light terminal B and electrical supply unit (ESU) terminal 2L. 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 power supply. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a short to power supply. Go to the next step.
5	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)].) Operate the room light switch to DOOR position. 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.
6	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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