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

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DTC P1794:16 [START STOP UNIT]

Description	Start stop unit power supply voltage (terminal 2W) low input
Detection condition	Start stop unit power supply circuit voltage (terminal 2W) of less than 6.5 V is detected for 5 s or more.
Fail-safe	Not applicable
Possible cause	DTCs are stored in the PCM. Battery malfunction Generator malfunction Start stop unit connector or terminal malfunction Start stop unit power supply circuit (terminal 2W) malfunction Short to ground in wiring harness between MAIN 200 A fuse and start stop unit terminal 2W AT 15 A fuse malfunction MAIN 200 A fuse malfunction Open circuit in wiring harness between battery positive terminal and start stop unit terminal 2W Start stop unit malfunction

Diagnostic Procedure

Step	Inspection		Action
1	VERIFY PCM DTCs Retrieve the PCM DTCs using the M-MDS. (See ON-BOARD DIAGNOSTIC TEST [PCM (SKYACTIV-G 2.0)].) Are any DTCs displayed?	Yes	Repair or replace the malfunctioning part according to the applicable DTC troubleshooting. (See DTC TABLE [PCM (SKYACTIV-G 2.0)].)
		No	Go to the next step.
2	INSPECT BATTERY Inspect the battery. (See BATTERY INSPECTION.) Is the battery normal?	Yes	Go to the next step.
		No	Recharge or replace the battery, then go to Step 6. (See BATTERY RECHARGING.) (See BATTERY REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
3	INSPECT GENERATOR Inspect the generator. (See GENERATOR INSPECTION [SKYACTIV-G 2.0].) Is the generator normal?	Yes	Go to the next step.
		No	Replace the generator, then go to Step 6. (See GENERATOR REMOVAL/INSTALLATION [SKYACTIV-G 2.0].)
4	INSPECT START STOP UNIT CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the start stop 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 6.
5	VERIFY START STOP UNIT POWER SUPPLY VOLTAGE (TERMINAL 2W) Always reconnect all disconnected connectors. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Display PID VPWR_B2 using the M-MDS. (See PID/DATA MONITOR INSPECTION [START STOP UNIT].) Is the voltage B+?	Yes	Go to the next step.
		No	Inspect the AT 15 A fuse and MAIN 200 A fuse. Any fuse is blown: Refer to the wiring diagram and verify whether or not there is a common connector between MAIN 200 A fuse and start stop unit terminal 2W. 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. Replace the fuse. Any fuse is damaged: Replace the fuse. All fuses are normal: Refer to the wiring diagram and verify whether or not there is a common connector between battery positive terminal and start stop unit terminal 2W. 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 the next step.
6	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 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	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.
7	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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