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

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DTC B126A:11 [BCM]

Description	Door lock-link switch (LH) lock circuit malfunction
Detection condition	BCM detects a short to ground in the door lock-link switch (LH) lock circuit with the door lock-link switch (LH) unlocked.
Fail-safe	Not applicable
Possible cause	Door latch and lock actuator (LH) connector or terminal malfunction Door lock-link switch (LH) malfunction Start stop unit connector or terminal malfunction BCM connector or terminal malfunction Short to ground in wiring harness between the following terminals: Door latch and lock actuator (LH) terminal D—BCM terminal 2A Start stop unit terminal 1P—Door latch and lock actuator (LH) terminal D Start stop unit malfunction 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].) Lock/unlock all the doors by operating the driver’s door lock knob. Retrieve the BCM DTCs using the M-MDS with the door lock-link switch (LH) unlocked. (See DTC INSPECTION [BCM].) Is the same DTC displayed?	Yes	Go to the next step.
		No	Go to Step 9.
2	INSPECT DOOR LATCH AND LOCK ACTUATOR (LH) CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the door latch and lock actuator (LH) 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 8.
3	INSPECT DOOR LOCK-LINK SWITCH (LH) Inspect the door lock-link switch (LH). (See DOOR LOCK-LINK SWITCH INSPECTION.) Is the door lock-link switch (LH) normal?	Yes	Go to the next step.
		No	Replace the door latch and lock actuator (LH), then go to Step 8. (See DOOR LATCH AND LOCK ACTUATOR REMOVAL/INSTALLATION.)
4	INSPECT START STOP UNIT CONNECTOR CONDITION 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 8.
5	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 8.
6	INSPECT DOOR LOCK-LINK SWITCH (LH) LOCK CIRCUIT FOR SHORT TO GROUND Verify that the door latch and lock actuator (LH), start stop unit and BCM connectors are disconnected. Inspect for continuity between door latch and lock actuator (LH) terminal D (wiring harness-side) and body ground. Is there continuity?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals: Door latch and lock actuator (LH) terminal D—BCM terminal 2A Start stop unit terminal 1P—Door latch and lock actuator (LH) terminal D 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 Step 8.
		No	Go to the next step.
7	INSPECT START STOP UNIT Inspect the start stop unit. (See START STOP UNIT INSPECTION.) Is the start stop unit normal?	Yes	Go to the next step.
		No	Replace the start stop unit, then go to the next step. (See START STOP UNIT REMOVAL/INSTALLATION.)
8	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].) Lock/unlock all the doors by operating the driver’s door lock knob. 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.
9	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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