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

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DTC U3003:16 [CONNECTIVITY MASTER UNIT]

Description	Low ACC power supply voltage input to connectivity master unit (CMU)
Detection condition	The connectivity master unit (CMU) detects ACC power supply circuit voltage of 8.0 ± 0.8 V or less for 10 s or more with the ignition switched to ACC or ON (engine off or on).
Fail-safe	Not applicable
Possible cause	DTCs are stored in the PCM. Battery malfunction Generator malfunction Connectivity master unit (CMU) connector or terminal malfunction Connectivity master unit (CMU) ACC power supply circuit malfunction Short to ground in wiring harness between MIRROR 7.5 A fuse and connectivity master unit (CMU) terminal 2Q MIRROR 7.5 A fuse malfunction Open circuit in wiring harness between ACC relay terminal C and connectivity master unit (CMU) terminal 2Q Connectivity master unit (CMU) 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 CONNECTIVITY MASTER UNIT (CMU) CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the connectivity master unit (CMU) 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 CONNECTIVITY MASTER UNIT (CMU) ACC POWER SUPPLY VOLTAGE Verify that the connectivity master unit (CMU) connector is disconnected. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Measure the voltage at connectivity master unit (CMU) terminal 2Q (wiring harness-side). Is the voltage B+?	Yes	Go to the next step.
		No	Inspect the MIRROR 7.5 A fuse. If the fuse is blown: Refer to the wiring diagram and verify if there is a common connector between MIRROR 7.5 A fuse and connectivity master unit (CMU) terminal 2Q. 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. If the fuse is normal: Refer to the wiring diagram and verify if there is a common connector between ACC relay terminal C and connectivity master unit (CMU) terminal 2Q. 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 connectivity master unit (CMU) using the M-MDS. (See CLEARING DTC [CONNECTIVITY MASTER UNIT].) Switch the ignition ON (engine off or on) and wait for 17 s or more. Retrieve the connectivity master unit (CMU) DTCs using the M-MDS. (See DTC INSPECTION [CONNECTIVITY MASTER UNIT].) Is the same DTC displayed?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the connectivity master unit (CMU). (See CONNECTIVITY MASTER UNIT (CMU) 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 [CONNECTIVITY MASTER UNIT].)
		No	DTC troubleshooting completed.

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