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

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DTC B1087:87 [CONNECTIVITY MASTER UNIT]

Description	Communication error with commander switch
Detection condition	The connectivity master unit (CMU) cannot receive a LIN signal from the commander switch for 5 s or more with the ignition switched ACC or ON (engine off or on).
Fail-safe	Not applicable
Possible cause	Commander switch connector or terminal malfunction Connectivity master unit (CMU) connector or terminal malfunction Short to ground in wiring harness between connectivity master unit (CMU) terminal 2K and commander switch terminal E Short to power supply in wiring harness between connectivity master unit (CMU) terminal 2K and commander switch terminal E Open circuit in wiring harness between connectivity master unit (CMU) terminal 2K and commander switch terminal E Commander switch malfunction Connectivity master unit (CMU) malfunction

Diagnostic Procedure

Step	Inspection		Action
1	INSPECT COMMANDER SWITCH CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the commander switch 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 COMMANDER SWITCH CIRCUIT FOR SHORT TO GROUND Verify that the commander switch and connectivity master unit (CMU) connectors are disconnected. Inspect for continuity between commander switch terminal E (wiring harness-side) and body ground. Is there continuity?	Yes	Refer to the wiring diagram and verify if there is a common connector between connectivity master unit (CMU) terminal 2K and commander switch terminal E. 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 COMMANDER SWITCH CIRCUIT FOR SHORT TO POWER SUPPLY Verify that the commander switch 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 commander switch terminal E (wiring harness-side). 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 connectivity master unit (CMU) terminal 2K and commander switch terminal E. 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 is shorted to power supply. Go to Step 7.
5	INSPECT COMMANDER SWITCH CIRCUIT FOR OPEN CIRCUIT Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Verify that the commander switch and connectivity master unit (CMU) connectors are disconnected. Inspect the wiring harness for continuity between connectivity master unit (CMU) terminal 2K (wiring harness-side) and commander switch terminal E (wiring harness-side). Is there continuity?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify if there is a common connector between connectivity master unit (CMU) terminal 2K and commander switch terminal E. 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 COMMANDER SWITCH 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 commander switch, then go to the next step. (See COMMANDER SWITCH 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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