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

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DTC U3003:16 [ELECTRICAL SUPPLY UNIT (ESU)]

Description	Electrical supply unit (ESU) power supply voltage low input
Detection condition	Electrical supply unit (ESU) power supply circuit (terminal 1H, 2P, or 2R) of less than 8 V is detected for 10 s or more.
Fail-safe	Not applicable
Possible cause	DTCs are stored in the PCM. Battery malfunction Generator malfunction Electrical supply unit (ESU) connector or terminal malfunction Electrical supply unit (ESU) power supply circuit malfunction Short to ground in the wiring harness between the following terminals: METER1 10 A fuse—Electrical supply unit (ESU) terminal 1H MAIN 200 A fuse—Electrical supply unit (ESU) terminal 2P MAIN 200 A fuse—Electrical supply unit (ESU) terminal 2R METER1 10 A fuse malfunction INTERIOR 15 A fuse malfunction ROOM 25 A fuse malfunction F.WASHER 15 A fuse malfunction CABIN+B 50 A fuse malfunction MAIN 200 A fuse malfunction Open circuit in wiring harness between the following terminals: IG1 relay—Electrical supply unit (ESU) terminal 1H Battery positive terminal—Electrical supply unit (ESU) terminal 2P Battery positive terminal—Electrical supply unit (ESU) terminal 2R Electrical supply unit (ESU) malfunction

Diagnostic Procedure

Step	Inspection		Action
1	VERIFY PCM DTCs Retrieve the PCM DTCs using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST [PCM (SKYACTIV-G 2.0)].) Are any DTCs displayed?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [PCM (SKYACTIV-G 2.0)].)
		No	Go to the next step.
2	INSPECT BATTERY Inspect the battery. (See BATTERY INSPECTION.) Is the battery normal?	Yes	Go to the next step.
		No	Recharge or replace the battery, then go to Step 6. (See BATTERY RECHARGING.) (See BATTERY REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
3	INSPECT GENERATOR Inspect the generator. (See GENERATOR INSPECTION [SKYACTIV-G 2.0].) Is the generator normal?	Yes	Go to the next step.
		No	Replace the generator, then go to Step 6. (See GENERATOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
4	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 6.
5	VERIFY ELECTRICAL SUPPLY UNIT (ESU) POWER SUPPLY VOLTAGE Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Measure the voltage at the following terminals (wiring harness-side): Electrical supply unit (ESU) terminal 1H Electrical supply unit (ESU) terminal 2P Electrical supply unit (ESU) terminal 2R Is the voltage B+?	Yes	Go to the next step.
		No	Inspect the METER1 10 A fuse, INTERIOR 15 A fuse, ROOM 25 A fuse, F.WASHER 15 A fuse, CABIN+B 50 A fuse and MAIN 200 A fuse. Any fuse is blown: Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: METER1 10 A fuse—Electrical supply unit (ESU) terminal 1H MAIN 200 A fuse—Electrical supply unit (ESU) terminal 2P MAIN 200 A fuse—Electrical supply unit (ESU) terminal 2R 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. Replace the fuse. Any fuse is damaged: Replace the fuse. All fuses are normal: Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: IG1 relay—Electrical supply unit (ESU) terminal 1H Battery positive terminal—Electrical supply unit (ESU) terminal 2P Battery positive terminal—Electrical supply unit (ESU) terminal 2R 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 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)].) Switch the ignition ON (engine off or on) and wait for 10 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.
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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