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

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DTC B1238:87 [CONNECTIVITY MASTER UNIT]

Description	HD image transfer circuit malfunction
Detection condition	The connectivity master unit (CMU) detects a communication error in the HD image transfer circuit for 20 times with the ignition switched ON (engine off or on).
Fail-safe	Not applicable
Possible cause	Tuner and amp unit (TAU) connector or terminal malfunction Connectivity master unit (CMU) connector or terminal malfunction Short to ground in wiring harness between the following terminals: Connectivity master unit (CMU) terminal 2O—Tuner and amp unit (TAU) terminal 1W Connectivity master unit (CMU) terminal 2P—Tuner and amp unit (TAU) terminal 1X Short to power supply in wiring harness between the following terminals: Connectivity master unit (CMU) terminal 2O—Tuner and amp unit (TAU) terminal 1W Connectivity master unit (CMU) terminal 2P—Tuner and amp unit (TAU) terminal 1X Open circuit in wiring harness between the following terminals: Connectivity master unit (CMU) terminal 2O—Tuner and amp unit (TAU) terminal 1W Connectivity master unit (CMU) terminal 2P—Tuner and amp unit (TAU) terminal 1X Tuner and amp unit (TAU) malfunction Connectivity master unit (CMU) malfunction

Diagnostic Procedure

Step	Inspection		Action
1	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 7.
2	INSPECT CONNECTIVITY MASTER UNIT (CMU) CONNECTOR CONDITION 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 7.
3	INSPECT HD IMAGE TRANSFER CIRCUIT FOR SHORT TO GROUND Verify that the tuner and amp unit (TAU) and connectivity master unit (CMU) connectors are disconnected. Inspect for continuity between the following terminals (wiring harness-side) and body ground: Tuner and amp unit (TAU) terminal 1W Tuner and amp unit (TAU) terminal 1X Is there continuity?	Yes	Refer to the wiring diagram and verify if there is a common connector between the following terminals: Connectivity master unit (CMU) terminal 2O—Tuner and amp unit (TAU) terminal 1W Connectivity master unit (CMU) terminal 2P—Tuner and amp unit (TAU) terminal 1X 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. Go to Step 7.
		No	Go to the next step.
4	INSPECT HD IMAGE TRANSFER CIRCUIT FOR SHORT TO POWER SUPPLY Verify that the tuner and amp unit (TAU) and connectivity master unit (CMU) connectors are disconnected. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Switch the ignition ON (engine off or on). Measure the voltage at the following terminals (wiring harness-side): Tuner and amp unit (TAU) terminal 1W Tuner and amp unit (TAU) terminal 1X Is the voltage 0 V?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify if there is a common connector between the following terminals: Connectivity master unit (CMU) terminal 2O—Tuner and amp unit (TAU) terminal 1W Connectivity master unit (CMU) terminal 2P—Tuner and amp unit (TAU) terminal 1X 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 power supply. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a short to power supply. Go to Step 7.
5	INSPECT HD IMAGE TRANSFER CIRCUIT FOR OPEN CIRCUIT Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Verify that the tuner and amp unit (TAU) and connectivity master unit (CMU) connectors are disconnected. Inspect for continuity between the following terminals (wiring harness-side): Connectivity master unit (CMU) terminal 2O—Tuner and amp unit (TAU) terminal 1W Connectivity master unit (CMU) terminal 2P—Tuner and amp unit (TAU) terminal 1X Is there continuity?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify if there is a common connector between the following terminals: Connectivity master unit (CMU) terminal 2O—Tuner and amp unit (TAU) terminal 1W Connectivity master unit (CMU) terminal 2P—Tuner and amp unit (TAU) terminal 1X 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 Step 7.
6	VERIFY IF MALFUNCTIONING LOCATION IS TUNER AND AMP UNIT (TAU) DEPENDING ON REPEATABILITY 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 12 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	Replace the tuner and amp unit (TAU), then go to the next step. (See TUNER AND AMP UNIT (TAU) REMOVAL/INSTALLATION.)
		No	Go to Step 8.
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 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 12 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.
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 [CONNECTIVITY MASTER UNIT].)
		No	DTC troubleshooting completed.

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