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

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DTC B1B71:11, B1B71:13 [CLIMATE CONTROL UNIT (MANUAL AIR CONDITIONER)]

System malfunction location	B1B71:11: Evaporator temperature sensor circuit short to ground B1B71:13: Evaporator temperature sensor circuit open
Detection condition	Malfunction in wiring harness between evaporator temperature sensor and climate control unit
Fail-safe function	A/C output OFF is controlled when the evaporator temperature sensor input value is at 0 °C {32 °F}.
Possible cause	Connector or terminal malfunction Evaporator temperature sensor malfunction Open circuit in wiring harness between climate control unit and evaporator temperature sensor Short to ground in wiring harness between climate control unit and evaporator temperature sensor Climate control unit malfunction

Diagnostic procedure

STEP	INSPECTION		ACTION
1	INSPECT EVAPORATOR TEMPERATURE SENSOR CONNECTOR Switch the ignition off. Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Disconnect the evaporator temperature sensor connector. (See EVAPORATOR TEMPERATURE SENSOR INSPECTION [MANUAL AIR CONDITIONER].) Inspect the connector and terminals (corrosion, damage, pin disconnection). Are the connector and terminals normal?	Yes	Go to the next step.
		No	Repair/replace the connector or terminal. After repair procedure, go to the next step.
2	INSPECT EVAPORATOR TEMPERATURE SENSOR Inspect the evaporator temperature sensor. (See EVAPORATOR TEMPERATURE SENSOR INSPECTION [MANUAL AIR CONDITIONER].) Is it normal?	Yes	Go to the next step.
		No	Replace the evaporator temperature sensor. (See A/C UNIT DISASSEMBLY/ASSEMBLY.) Go to the next step.
3	INSPECT EVAPORATOR TEMPERATURE SENSOR CIRCUIT FOR OPEN CIRCUIT Disconnect the climate control unit connector. (See CLIMATE CONTROL UNIT REMOVAL/INSTALLATION [MANUAL AIR CONDITIONER].) Disconnect the evaporator temperature sensor connector. (See EVAPORATOR TEMPERATURE SENSOR INSPECTION [MANUAL AIR CONDITIONER].) Inspect for continuity between the following terminals (wiring harness-side): Climate control unit terminal E???evaporator temperature sensor terminal A Climate control unit terminal J???evaporator temperature sensor terminal B 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 climate control unit terminal and evaporator temperature sensor terminal. 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.
4	INSPECT EVAPORATOR TEMPERATURE SENSOR CIRCUIT FOR SHORT TO GROUND Inspect for continuity between the following terminal (wiring harness-side) and body ground: Climate control unit terminal J Is there continuity?	Yes	Refer to the wiring diagram and verify whether or not there is a common connector between climate control unit terminal and evaporator temperature sensor terminal. 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	Connect the climate control unit connector, then go to the next step.
5	VERIFY CLIMATE CONTROL UNIT CONNECTOR CONDITION Inspect the connector and terminals (corrosion, damage, pin disconnection). Are the connector and terminals normal?	Yes	Go to the next step.
		No	Repair/replace the malfunctioning vehicle wiring harness, connector, or terminal. After repair procedure, go to the next step.
6	INSPECT EVAPORATOR TEMPERATURE SENSOR CIRCUIT Connect the climate control unit connector. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Switch the ignition ON (engine off or on). Inspect the voltage at the following climate control unit terminal (wiring harness-side). Terminal J (evaporator temperature sensor input signal) Is the voltage normal? (Approx. 5 V)	Yes	The system is normal at present. Go to the next step.
		No	Go to the next step.
7	VERIFY THAT SAME DTC IS NOT OUTPUT AGAIN Switch the ignition off. Disconnect the negative battery cable. Reconnect the disconnected connectors. Connect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION.) Clear the past malfunction from memory. (See CLEARING DTC [CLIMATE CONTROL UNIT (MANUAL AIR CONDITIONER)].) Verify DTCs. (See DTC DISPLAY [CLIMATE CONTROL UNIT (MANUAL AIR CONDITIONER)].) Is DTC B1B71:11 or B1B71:13 output?	Yes	Repeat the inspection from Step 1. If the malfunction does not recur, go to the next step. If the malfunction recurs, replace the climate control unit. (See CLIMATE CONTROL UNIT REMOVAL/INSTALLATION [MANUAL AIR CONDITIONER].) Go to the next step.
		No	Go to the next step.
8	VERIFY THAT NO OTHER DTCs ARE PRESENT Verify other DTCs displayed. (See DTC DISPLAY [CLIMATE CONTROL UNIT (MANUAL AIR CONDITIONER)].) Are any other DTCs output?	Yes	Perform the corresponding DTC inspection. (See DTC TABLE [CLIMATE CONTROL UNIT (MANUAL AIR CONDITIONER)].)
		No	DTC troubleshooting completed.

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