B1203

General Description

Engine coolant temperature sensor is located in the engine coolant passage of the cylinder head for detecting the engine coolant temperature. It contains negative type thermistor whoses resistance value is in inverse proportion to temperature. Resistance of water-sensor that varies with temperature makes signal voltage of A/C ECU change. In this way A/C ECU detects temperature. Signal of water sensor is used for cold engine lockout control - When the driver operates the heater before the engine is warmed up enough, to prevent driver from unpleasantness of cold air. the heater control unit reduces blower motor speed until coolant temperature reaches the threshold value.

DTC Description

Air conditioner Control Module sets DTC B1203 if Engine coolant temperature sensor has been detected open or below 0.1V for 4sec.

DTC Detecting Condition






Specification

** Resistance value of Engine coolant temperature sensor as a function of temperature.






Diagnostic Circuit Diagram






Monitor Scantool Data

1. Connect scantool with diagnostic connector.
2. Warm up the engine to normal engine temperature after engine starts.
3. Select and monitor "Water temperature sensor" parameter.






Fig 1) Parameter of "WATER TEMP.SENSOR" will be fixed at 85°C(185°F), if there is any fault in INCAR SENSOR.
4. Is the Water temperature sensor normal ?






Terminal & Connector Inspection

1. Many malfunctions in the electrical system are caused by poor harness and terminals. Faults can also be caused by interference from other electrical systems, and mechanical or chemical damage.
2. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration,or damage.
3. Has a problem been found?






Signal Circuit Inspection

Check short to ground in harness
1. Ignition "OFF".
2. Disconnect Water temp.sensor and Connect A/C control unit main harness connector.
3. Measure resistance between Signal(+) terminal of Water temp.sensor harness connector and chassis ground.

Specification :Infinity

4. Is the measured resistance within specification?






Component Inspection

Check Incar temp.sensor
1. Ignition "OFF".
2. Disconnect Water temp.sensor and Connect A/C control unit main harness connector.
3. Measure resistance between Signal(+) terminal of Water temp.sensor harness connector and Sensor ground harness connector.

Specification :Refer the specifications in fig.1

FIG.1) ** Specifications : Resistance value of Water sensor as a function of temperature.






4. Is "resistance" display near the specified value?






Check A/C-ECU
1. Ignition "OFF".
2. Disconnect Water temp.sensor and Connect A/C control unit main harness connector.
3. Ignition "ON"(ENGINE "OFF").
4. Measure voltage between Signal(+) terminal of Water temp.sensor harness connector and chassis ground.

Specification :Approx. 5V

5. Is "voltage" display near the specified value?






Verification of Vehicle Repair

After a repair, it is essential to verify that the fault has been corrected.
1. Connect scantool and select "Diagnostic Trouble Codes(DTCs)" mode and then clear DTC.
2. Operate the vehicle and monitor the DTC on the scantool.
3. Are any DTCs present?