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

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DTC B13C3:16 [START STOP UNIT]

Description	LF control unit power supply voltage low input
Detection condition	Start stop unit power supply circuit voltage of 8.5 V or more or less than 16.5 V and LF control unit power supply circuit voltage of 5 V or more or less than 8.5 V are detected for 5 s or more.
Fail-safe	Inhibits the door lock/unlock control using the advanced keyless entry system.
Possible cause	LF control unit connector or terminal malfunction Malfunction between battery positive terminal and LF control unit terminal B LF control unit malfunction Start stop unit malfunction

Diagnostic Procedure

Step	Inspection		Action
1	INSPECT LF CONTROL UNIT CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the LF control unit 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 4.
2	VERIFY LF CONTROL UNIT POWER SUPPLY VOLTAGE Always reconnect all disconnected connectors. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Measure the voltage at the LF control unit terminal B (wiring harness-side). Is the voltage 5 V or more or less than 8.5 V?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector between battery positive terminal and LF control unit 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 a malfunction. Repair or replace the malfunctioning part. If there is no common connector: Inspect the wiring harness between battery positive terminal and LF control unit terminal B. If there is any malfunction: Repair or replace the wiring harness. If there is no malfunction: Replace the LF control unit. (See LF CONTROL UNIT REMOVAL/INSTALLATION.) Go to Step 4.
		No	Go to the next step.
3	INSPECT LF CONTROL UNIT Inspect the LF control unit. (See LF CONTROL UNIT INSPECTION.) Is the LF control unit normal?	Yes	Go to the next step.
		No	Replace the LF control unit, then go to the next step. (See LF CONTROL UNIT REMOVAL/INSTALLATION.)
4	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 start stop unit using the M-MDS. (See CLEARING DTC [START STOP UNIT].) Switch the ignition ON (engine off) and wait for 5 s or more. Retrieve the start stop unit DTCs using the M-MDS. (See DTC INSPECTION [START STOP UNIT].) Is the same DTC displayed?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the start stop unit. (See START STOP UNIT REMOVAL/INSTALLATION.) Go to the next step.
		No	Go to the next step.
5	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 [START STOP UNIT].)
		No	DTC troubleshooting completed.

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