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

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DTC U0140:00 [ELECTRICAL SUPPLY UNIT (ESU)]

Description	Communication error with BCM
Detection condition	Electrical supply unit (ESU) could not receive the CAN signal from the BCM for 2 s or more with the ignition switched ON (engine off or on).
Fail-safe	Exterior lighting system When the ignition is switched ON (engine off or on), the headlights LO, TNS (parking lights), and panel light turn on and other exterior light controls are stopped. Interior light control system Turn the interior light off when the room light switch is in the DOOR position.
Possible cause	BCM connector or terminal malfunction Electrical supply unit (ESU) connector or terminal malfunction Short to ground in wiring harness between BCM terminal 2Y and electrical supply unit (ESU) terminal 2I Short to power supply in wiring harness between BCM terminal 2Y and electrical supply unit (ESU) terminal 2I Open circuit in wiring harness between BCM terminal 2Y and electrical supply unit (ESU) terminal 2I BCM malfunction Electrical supply unit (ESU) malfunction

Diagnostic Procedure

Step	Inspection		Action
1	INSPECT BCM CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the BCM 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.
2	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.
3	INSPECT LIN COMMUNICATION CIRCUIT BETWEEN BCM AND ELECTRICAL SUPPLY UNIT (ESU) FOR SHORT TO GROUND Verify that the BCM and electrical supply unit (ESU) connectors are disconnected. Inspect for continuity between BCM terminal 2Y (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 BCM terminal 2Y and electrical supply unit (ESU) terminal 2I. 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 7.
		No	Go to the next step.
4	INSPECT LIN COMMUNICATION CIRCUIT BETWEEN BCM AND ELECTRICAL SUPPLY UNIT (ESU) FOR SHORT TO POWER SUPPLY Verify that the BCM 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 BCM terminal 2Y (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 BCM terminal 2Y and electrical supply unit (ESU) terminal 2I. 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 Step 7.
5	INSPECT LIN COMMUNICATION CIRCUIT BETWEEN BCM AND ELECTRICAL SUPPLY UNIT (ESU) FOR OPEN CIRCUIT Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Verify that the BCM and electrical supply unit (ESU) connectors are disconnected. Inspect the wiring harness for continuity between BCM terminal 2Y (wiring harness-side) and electrical supply unit (ESU) terminal 2I (wiring harness-side). Is there continuity?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify whether or not there is a common connector between BCM terminal 2Y and electrical supply unit (ESU) terminal 2I. 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 an open circuit. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has an open circuit. Go to Step 7.
6	VERIFY IF MALFUNCTIONING LOCATION IS BCM 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)].) Switch the ignition ON (engine off or on) and wait for 2 s or more. 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 BCM, then go to the next step. (See BODY CONTROL MODULE (BCM) REMOVAL/INSTALLATION.)
		No	Go to Step 8.
7	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)].) Switch the ignition ON (engine off or on) and wait for 2 s or more. 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.
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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