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

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DTC U3003:16 [BCM]

Description	BCM power supply voltage low input
Detection condition	The BCM detected a BCM power supply circuit (terminals 1B and 1A) voltage of less than 10 V for 10 s or more with the ignition switched ON (engine off or on).
Fail-safe	Not applicable
Possible cause	DTCs are stored in the PCM. Battery malfunction Generator malfunction BCM connector or terminal malfunction BCM power supply circuit malfunction Short to ground in the wiring harness between the following: MAIN 200 A fuse—BCM terminal 1B MAIN 200 A fuse—BCM terminal 1A INTERIOR 15 A fuse malfunction ROOM 25 A fuse malfunction HAZARD 15 A fuse malfunction MAIN 200 A fuse malfunction Open circuit in wiring harness between the following terminals: Battery positive terminal—BCM terminal 1B Battery positive terminal—BCM terminal 1A 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 10 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 8.
2	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.
3	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 7. (See BATTERY RECHARGING.) (See BATTERY REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
4	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 7. (See GENERATOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
5	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.
6	VERIFY BCM POWER SUPPLY VOLTAGE Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Measure the voltage at the following terminals (wiring harness-side): BCM terminal 1B BCM terminal 1A Is the voltage B+?	Yes	Go to the next step.
		No	Inspect the INTERIOR 15 A fuse, ROOM 25 A fuse, HAZARD 15 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: MAIN 200 A fuse—BCM terminal 1B MAIN 200 A fuse—BCM terminal 1A 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: Battery positive terminal—BCM terminal 1B Battery positive terminal—BCM terminal 1A 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.
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 BCM using the M-MDS. (See CLEARING DTC [BCM].) Switch the ignition ON (engine off or on) and wait for 10 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.
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 [BCM].)
		No	DTC troubleshooting completed.

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