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

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DTC B124C:56 [START STOP UNIT]

Description	Turn switch internal circuit malfunction
Detection condition	Start stop unit detects that the turn switch LH and RH are turned on simultaneously for 5 s or more.
Fail-safe	Not applicable
Possible cause	Start stop unit configuration error The installations of the light switch and the wiper and washer switch are reversed. Turn switch malfunction Start stop unit malfunction
System wiring diagram	Not applicable

Diagnostic Procedure

Step	Inspection		Action
1	PERFORM START STOP UNIT CONFIGURATION (USING AS-BUILT DATA) Using the M-MDS, perform the start stop unit configuration (using As-Built data). (See START STOP UNIT CONFIGURATION (USING AS-BUILT DATA).) Clear the DTC for the start stop unit using the M-MDS. (See CLEARING DTC [START STOP UNIT].) Operate the turn switch to RH position and wait for 5 s or more. Operate the turn switch to LH position 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	Using the M-MDS, perform the start stop unit configuration (using As-Built data) again, then go to the next step. (See START STOP UNIT CONFIGURATION (USING AS-BUILT DATA).)
		No	Go to Step 5.
2	VERIFY IF INSTALLATIONS OF LIGHT SWITCH AND WIPER AND WASHER SWITCH ARE REVERSED Verify the installation condition of the light switch and the wiper and washer switch. Are the light switch and the wiper and washer switch installed correctly?	Yes	Go to the next step.
		No	Install the light switch and the wiper and washer switch properly, then go to Step 4. (See LIGHT SWITCH REMOVAL/INSTALLATION.) (See WIPER AND WASHER SWITCH REMOVAL/INSTALLATION.)
3	INSPECT TURN SWITCH Inspect the turn switch. (See LIGHT SWITCH INSPECTION.) Is the turn switch normal?	Yes	Go to the next step.
		No	Replace the light switch, then go to the next step. (See LIGHT SWITCH REMOVAL/INSTALLATION.)
4	VERIFY THAT REPAIRS HAVE BEEN COMPLETED Clear the DTC for the start stop unit using the M-MDS. (See CLEARING DTC [START STOP UNIT].) Operate the turn switch to RH position and wait for 5 s or more. Operate the turn switch to LH position and wait for 5 s or more. Perform the start stop unit DTC inspection 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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