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

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DTC U3003:16/U3003:17/U3003:1E [DSC HU/CM]

DTC	U3003:16	Power supply
	U3003:17
	U3003:1E
DETECTION CONDITION		Power supply malfunction is detected.
FAIL-SAFE FUNCTION		Refer to “Fail-safe function table”. (See DTC TABLE [DSC HU/CM].)
POSSIBLE CAUSE		DTC is stored in PCM Battery malfunction Generator malfunction Fuse (SRS1 7.5A, ABS/DSC S 30A, ABS/DSC M 50A) malfunction Short to ground or open circuit in wiring harness between battery and DSC HU/CM terminal I Short to ground or open circuit in wiring harness between battery and DSC HU/CM terminal A Short to ground or open circuit in wiring harness between battery and DSC HU/CM terminal B Open circuit in wiring harness between DSC HU/CM terminal AK and body ground Poor connection at each connector DSC HU/CM malfunction

Diagnostic Procedure

Step	Inspection		Action
1	VERIFY PCM DTC Using the M-MDS, perform the PCM DTC inspection. (See ON-BOARD DIAGNOSTIC TEST [PCM (SKYACTIV-G 2.0)].) Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [PCM (SKYACTIV-G 2.0)].) DTC troubleshooting completed, then go to the next step.
		No	Go to the next step.
2	INSPECT BATTERY Inspect the battery. (See BATTERY INSPECTION.) Is there any malfunction?	Yes	Charge or replace the battery, then go to Step7. (See BATTERY RECHARGING.) (See BATTERY REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
		No	Go to the next step.
3	INSPECT GENERATOR Inspect the generator. (See GENERATOR INSPECTION [SKYACTIV-G 2.0].) Is there any malfunction?	Yes	Replace the generator, then go to Step7. (See GENERATOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
		No	Go to the next step.
4	INSPECT FUSE CONDITION Is the fuse (SRS1 7.5A, ABS/DSC S 30A, ABS/DSC M 50A) normal?	Yes	Go to the next step.
		No	If the fuse is blown: Refer to the wiring diagram and verify whether or not there is a common connector between fuse and DSC HU/CM terminal I, A and B. 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. If the fuse is damaged: Replace the fuse. Go to Step7.
5	INSPECT DSC HU/CM POWER CIRCUIT FOR OPEN CIRCUIT Switch the ignition OFF. Disconnect the DSC HU/CM connector. Switch the ignition ON (engine off). Measure the voltage as followings: DSC HU/CM terminal I (wiring harness-side)—body ground DSC HU/CM terminal A (wiring harness-side)—body ground DSC HU/CM terminal B (wiring harness-side)—body ground Is the voltage 10 V or more?	Yes	Go to the next Step.
		No	Refer to the wiring diagram and verify whether or not there is a common connector in the followings. Battery—DSC HU/CM terminal I Battery—DSC HU/CM terminal A Battery—DSC HU/CM terminal B 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 Step7.
6	INSPECT DSC HU/CM GROUND CIRCUIT FOR OPEN CIRCUIT OR POOR GROUND Switch the ignition OFF. Disconnect the DSC HU/CM connector. Measure the resistance between DSC HU/CM terminal AK (wiring harness-side) and body ground. Is the resistance 0—1 ohm?	Yes	Go to the next step.
		No	If the open circuit could be detected in the wiring harness: Refer to the wiring diagram and verify whether or not there is a common connector between DSC HU/CM terminal AK and body ground. 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. If the resistance is out of specification: Refer to the wiring diagram and verify whether or not there is a common connector between DSC HU/CM terminal AK and body ground. 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 poor ground. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a poor ground. Go to the next step.
7	VERIFY DTC TROUBLESHOOTING COMPLETED Using the M-MDS, clear the DTC from the DSC HU/CM. (See CLEARING DTC [DSC HU/CM].) Using the M-MDS, perform the DSC HU/CM DTC inspection. (See DTC INSPECTION [DSC HU/CM].) Is the same DTC present?	Yes	Repeat the inspection from Step1 If the malfunction recurs, replace the DSC HU/CM, then go to the next step. (See DSC HU/CM REMOVAL/INSTALLATION.)
		No	Go to the next step.
8	VERIFY NO DTC IS PRESENT Are any DTCs present?	Yes	Go to the applicable DTC inspection. (See DTC TABLE [DSC HU/CM].)
		No	DTC troubleshooting completed.

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