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

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DTC U0231:68 [BCM]

Description	Communication error with auto light sensor/rain sensor
Detection condition	BCM could not receive the signals from the auto light sensor/rain sensor for 5 s or more with the ignition switched ON (engine off or on).
Fail-safe	Auto light system Continue the controls prior to the auto light malfunction detection. Auto wiper system Continue the controls prior to the wiper malfunction detection.
Possible cause	Auto light sensor/rain sensor connector or terminal malfunction BCM connector or terminal malfunction Short to ground in wiring harness between auto light sensor/rain sensor terminal A and BCM terminal 3X Short to power supply in wiring harness between auto light sensor/rain sensor terminal A and BCM terminal 3X Open circuit in wiring harness between auto light sensor/rain sensor terminal A and BCM terminal 3X Auto light sensor/rain sensor 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].) Operate the light switch to the AUTO position. Operate the wiper and washer switch to the AUTO position. Switch the ignition ON (engine off or on) and wait for 5 s or more. 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 9.
2	INSPECT AUTO LIGHT SENSOR/RAIN SENSOR CONNECTOR CONDITION Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the auto light sensor/rain sensor 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 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.
4	INSPECT AUTO LIGHT SENSOR/RAIN SENSOR CIRCUIT FOR SHORT TO GROUND Verify that the auto light sensor/rain sensor and BCM connectors are disconnected. Inspect for continuity between BCM terminal 3X (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 auto light sensor/rain sensor terminal A and BCM terminal 3X. 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.
5	INSPECT AUTO LIGHT SENSOR/RAIN SENSOR CIRCUIT FOR SHORT TO POWER SUPPLY Verify that the auto light sensor/rain sensor and BCM connectors are disconnected. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Switch the ignition ON (engine off or on). Measure the voltage at the BCM terminal 3X (wiring harness-side). Is the voltage 0 V?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify whether or not there is a common connector between auto light sensor/rain sensor terminal A and BCM terminal 3X. 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 power supply. Repair or replace the malfunctioning part. If there is no common connector: Repair or replace the wiring harness which has a short to power supply. Go to Step 8.
6	INSPECT AUTO LIGHT SENSOR/RAIN SENSOR CIRCUIT FOR OPEN CIRCUIT Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Verify that the auto light sensor/rain sensor and BCM connectors are disconnected. Inspect the wiring harness for continuity between auto light sensor/rain sensor terminal A (wiring harness-side) and BCM terminal 3X (wiring harness-side). Is there continuity?	Yes	Go to the next step.
		No	Refer to the wiring diagram and verify whether or not there is a common connector between auto light sensor/rain sensor terminal A and BCM terminal 3X. 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 Step 8.
7	VERIFY IF MALFUNCTIONING LOCATION IS AUTO LIGHT SENSOR/RAIN SENSOR DEPENDING ON REPEATABILITY 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].) Operate the light switch to the AUTO position. Operate the wiper and washer switch to the AUTO position. Switch the ignition ON (engine off or on) and wait for 5 s or more. Retrieve the BCM DTCs using the M-MDS. (See DTC INSPECTION [BCM].) Is the same DTC displayed?	Yes	Replace the auto light sensor/rain sensor, then go to the next step. (See RAIN SENSOR REMOVAL/INSTALLATION.)
		No	Go to Step 9.
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].) Operate the light switch to the AUTO position. Operate the wiper and washer switch to the AUTO position. Switch the ignition ON (engine off or on) and wait for 5 s or more. 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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