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

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DTC B1238:16 [CONNECTIVITY MASTER UNIT]

Description	Tuner and amp unit (TAU) low power supply voltage input
Detection condition	Connectivity master unit (CMU) detects power supply circuit voltage for tuner and amp unit (TAU) 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 Tuner and amp unit (TAU) connector or terminal malfunction Tuner and amp unit (TAU) power supply circuit malfunction Short to ground in wiring harness between MAIN 200 A fuse and tuner and amp unit (TAU) terminal 2B AUDIO2 15 A fuse malfunction AUDIO1 25 A fuse malfunction CABIN+B 50 A fuse malfunction MAIN 200 A fuse malfunction Open circuit in wiring harness between battery positive terminal and tuner and amp unit (TAU) terminal 2B Tuner and amp unit (TAU) 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 TUNER AND AMP UNIT (TAU) CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the tuner and amp unit (TAU) 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 TUNER AND AMP UNIT (TAU) POWER SUPPLY VOLTAGE Verify that the tuner and amp unit (TAU) connector is disconnected. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Switch the ignition ON (engine off or on). Measure the voltage at tuner and amp unit (TAU) terminal 2B (wiring harness-side). Is the voltage 10 V or more?	Yes	Go to the next step.
		No	Inspect the AUDIO2 15 A fuse, AUDIO1 25 A fuse, CABIN+B 50 A fuse, and MAIN 200 A fuse. Any fuse is blown: Refer to the wiring diagram and verify if there is a common connector between MAIN 200 A fuse and tuner and amp unit (TAU) terminal 2B. 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 if there is a common connector between battery positive terminal and tuner and amp unit (TAU) terminal 2B. 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 tuner and amp unit (TAU). (See TUNER AND AMP UNIT (TAU) 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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