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

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DTC U0447:86 [START STOP UNIT]

Description	Error signal received from BCM
Detection condition	Start stop unit receives the error signals from the BCM for 5 s or more with the ignition switched ON (engine off or on).
Fail-safe	Sets to default signal.
Possible cause	DTCs are stored in the BCM. BCM malfunction Start stop unit malfunction
System wiring diagram	Not applicable

Diagnostic Procedure

Step	Inspection		Action
1	VERIFY BCM DTCs Retrieve the BCM DTCs using the M-MDS. (See DTC INSPECTION [BCM].) Are any DTCs displayed?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [BCM].)
		No	Go to the next step.
2	VERIFY IF MALFUNCTIONING LOCATION IS BCM DEPENDING ON REPEATABILITY Clear the DTC for the start stop unit using the M-MDS. (See CLEARING DTC [START STOP UNIT].) Switch the ignition ON (engine off or on) 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	Replace the BCM, then go to the next step. (See BODY CONTROL MODULE (BCM) REMOVAL/INSTALLATION.)
		No	Go to Step 4.
3	VERIFY THAT REPAIRS HAVE BEEN COMPLETED Clear the DTC for the start stop unit using the M-MDS. (See CLEARING DTC [START STOP UNIT].) Switch the ignition ON (engine off or on) 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	Replace the start stop unit, then go to the next step. (See START STOP UNIT REMOVAL/INSTALLATION.)
		No	Go to the next step.
4	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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