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

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DTC B111E:12 [ELECTRICAL SUPPLY UNIT (ESU)]

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

Diagnostic Procedure

Step	Inspection		Action
1	VISUALLY INSPECT TRUNK COMPARTMENT LIGHT BULB Visually inspect the trunk compartment light bulb. Is the trunk compartment light bulb normal?	Yes	Go to the next step.
		No	Replace the trunk compartment light bulb, then go to Step 6. (See TRUNK COMPARTMENT LIGHT BULB REMOVAL/INSTALLATION.)
2	INSPECT TRUNK COMPARTMENT LIGHT CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the trunk compartment 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 6.
3	INSPECT TRUNK COMPARTMENT LIGHT Inspect the trunk compartment light. (See TRUNK COMPARTMENT LIGHT INSPECTION.) Is the trunk compartment light normal?	Yes	Go to the next step.
		No	Replace the trunk compartment light, then go to Step 6. (See TRUNK COMPARTMENT LIGHT REMOVAL/INSTALLATION.)
4	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 6.
5	INSPECT TRUNK COMPARTMENT LIGHT CIRCUIT FOR SHORT TO POWER SUPPLY Verify that the trunk compartment 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 the trunk compartment 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 trunk compartment light terminal B and electrical supply unit (ESU) terminal 2F. 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.
6	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)].) Open the trunk and turn the trunk compartment light switch on. 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.
7	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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