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

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DTC B1178:11 [BCM]

Description	Trunk lid latch switch circuit malfunction
Detection condition	BCM detects short to ground in trunk lid latch switch circuit with the trunk closed (trunk lid latch switch off).
Fail-safe	Not applicable
Possible cause	Trunk lid latch switch connector or terminal malfunction Trunk lid latch switch malfunction BCM connector or terminal malfunction Short to ground in wiring harness between trunk lid latch switch terminal A and BCM terminal 2AC BCM malfunction

Diagnostic Procedure

Step	Inspection		Action
1	VERIFY BCM DTCs AGAIN Clear the DTC for the BCM using the M-MDS. (See CLEARING DTC [BCM].) Open/close the trunk. Retrieve the BCM DTCs using the M-MDS. (See DTC INSPECTION [BCM].) Is the same DTC displayed?	Yes	Go to the next step.
		No	Go to Step 7.
2	INSPECT TRUNK LID LATCH SWITCH CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the trunk lid latch 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 6.
3	INSPECT TRUNK LID LATCH SWITCH Inspect the trunk lid latch switch. (See TRUNK LID OPENER SWITCH INSPECTION.) Is the trunk lid latch switch normal?	Yes	Go to the next step.
		No	Replace the trunk lid latch and release actuator, then go to Step 6. (See TRUNK LID LATCH AND RELEASE ACTUATOR REMOVAL/INSTALLATION.)
4	INSPECT BCM CONNECTOR CONDITION Disconnect the BCM 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	INSPECT TRUNK LID LATCH SWITCH CIRCUIT FOR SHORT TO GROUND Verify that the trunk lid latch switch and BCM connectors are disconnected. Inspect for continuity between trunk lid latch switch terminal A (wiring harness) and body ground. Is there continuity?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector between trunk lid latch switch terminal A and BCM terminal 2AC. 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 the next step.
		No	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 BCM using the M-MDS. (See CLEARING DTC [BCM].) Open/close the trunk. Retrieve the BCM DTCs using the M-MDS. (See DTC INSPECTION [BCM].) Is the same DTC displayed?	Yes	Repeat the inspection from Step 1. If the malfunction recurs, replace the BCM. (See BODY CONTROL MODULE (BCM) 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 [BCM].)
		No	DTC troubleshooting completed.

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