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

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DTC U0142:68 [BCM]

Description	Communication error with electrical supply unit (ESU)
Detection condition	BCM could not receive the signals from the electrical supply unit (ESU) for 5 s or more with the ignition switched ON (engine off or on).
Fail-safe	Exterior lighting system Turn the TNS (parking lights) and headlights LO on, and turn off other exterior light controls.
Possible cause	Electrical supply unit (ESU) connector or terminal malfunction BCM connector or terminal malfunction Short to ground in wiring harness between electrical supply unit (ESU) terminal 2I and BCM terminal 2Y Short to power supply in wiring harness between electrical supply unit (ESU) terminal 2I and BCM terminal 2Y Open circuit in wiring harness between electrical supply unit (ESU) terminal 2I and BCM terminal 2Y Electrical supply unit (ESU) malfunction BCM malfunction

Diagnostic Procedure

Step	Inspection		Action
1	VERIFY BCM DTCs AGAIN Clear the DTC for the BCM using the M-MDS. (See CLEARING DTC [BCM].) Switch the ignition ON (engine off or on) and wait for 5 s or more. Retrieve the BCM DTCs using the M-MDS. (See DTC INSPECTION [BCM].) Is the same DTC displayed?	Yes	Go to the next step.
		No	Go to Step 9.
2	INSPECT ELECTRICAL SUPPLY UNIT (ESU) CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) 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 8.
3	INSPECT BCM CONNECTOR CONDITION 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 8.
4	INSPECT ELECTRICAL SUPPLY UNIT (ESU) CIRCUIT FOR SHORT TO GROUND Verify that the electrical supply unit (ESU) and BCM 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 electrical supply unit (ESU) terminal 2I and BCM terminal 2Y. 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 8.
		No	Go to the next step.
5	INSPECT ELECTRICAL SUPPLY UNIT (ESU) CIRCUIT FOR SHORT TO POWER SUPPLY Verify that the electrical supply unit (ESU) and BCM 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 electrical supply unit (ESU) terminal 2I and BCM terminal 2Y. 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 8.
6	INSPECT ELECTRICAL SUPPLY UNIT (ESU) CIRCUIT FOR OPEN CIRCUIT Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Verify that the electrical supply unit (ESU) and BCM connectors are disconnected. Inspect the wiring harness for continuity between electrical supply unit (ESU) terminal 2I (wiring harness-side) and BCM terminal 2Y (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 electrical supply unit (ESU) terminal 2I and BCM terminal 2Y. 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 8.
7	VERIFY IF MALFUNCTIONING LOCATION IS ELECTRICAL SUPPLY UNIT (ESU) DEPENDING ON REPEATABILITY Always reconnect all disconnected connectors. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Clear the DTC for the BCM using the M-MDS. (See CLEARING DTC [BCM].) Switch the ignition ON (engine off or on) and wait for 5 s or more. Retrieve the BCM DTCs using the M-MDS. (See DTC INSPECTION [BCM].) Is the same DTC displayed?	Yes	Replace the electrical supply unit (ESU), then go to the next step. (See ELECTRICAL SUPPLY UNIT (ESU) REMOVAL/INSTALLATION.)
		No	Go to Step 9.
8	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 BCM using the M-MDS. (See CLEARING DTC [BCM].) Switch the ignition ON (engine off or on) and wait for 5 s or more. Retrieve the BCM DTCs using the M-MDS. (See DTC INSPECTION [BCM].) Is the same DTC displayed?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the BCM. (See BODY CONTROL MODULE (BCM) REMOVAL/INSTALLATION.) Go to the next step.
		No	Go to the next step.
9	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 [BCM].)
		No	DTC troubleshooting completed.

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