B1203
DTC B1203 WATER TEMPERATURE SENSOR SHORT (LOW)Component Location:
GENERAL DESCRIPTION
A water temp sensor located at heater unit detects coolant temperature. It contains negative type thermistor whose 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
The ECM sets DTC B1203 if there is a short circuit In water temp sensor signal harness or the measured resistance value of the sensor is less than the threshold value (1.27 kohms)
DTC Detecting Condition:
Signal Waveform And Data:
Schematic Diagram:
MONITOR DTC STATUS
1. Connect scantool to Data Link Connector (DLC).
2. Warm up the engine to normal operating temperature.
3. Monitor DTC (Diagnostics Trouble Code) on the scantool.
4. Is the same DTC displayed again?
YES - Go to "Inspection/Repair" procedure
NO - Fault is intermittent caused by poor contact In the sensor's and/or A/C-ECM connector or was repaired and A/C-ECM memory was not cleared. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of vehicle Repair" procedure.
W/HARNESS 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?
YES - Repair as necessary and go to "Verification of Vehicle Repair" procedure
NO - Go to "Signal circuit Short Inspection" procedure.
SIGNAL CIRCUIT SHORT INSPECTION
1. Ignition "OFF"
2. A/C-ECU : Connect, Water temp. sensor : Disconnect.
3. Measure resistance between Signal (+) terminal of Water temp. sensor harness connector and and chassis ground.
Specification : Infinity
4. Is "resistance" display near the specified value?
YES - Go to "Component Inspection" procedure.
NO
- Check for short to ground in harness.
- Repair as necessary and then go to "Verification of Vehicle Repair" procedure.
COMPONENT INSPECTION
CHECK WATER TEMP. SENSOR
1. Ignition "OFF"
2. A/C-ECU, Water temp. sensor : Connect.
3. Measure resistance between Signal (+) terminal of Water temp. sensor harness connector and and Sensor ground harness connector. (Component side)
Specification : Refer the specifications in fig.1
# Specifications : Resistance value of water temp sensor as a function of temperature.
# The actual value may differ from it according to various engine condition.
4. Is "resistance" display near the specified value?
YES - Go to "Check A/C-ECU" procedure
NO - Substitute with a known-good Water temp. sensor and check for proper operation If the problem is corrected, replace Water temp. sensor and then go to "Verification of Vehicle Repair" procedure.
CHECK A/C-ECU
1. Ignition "OFF".
2. A/C-ECU : Connect, Water temp. sensor : Disconnect.
3. Ignition "ON" (ENGINE "OFF").
4. Measure voltage between Signal (+) terminal of Water temp. sensor connector and and chassis ground. (Component side)
Specification: approx. 5 V
5. Is "voltage" display near the specified value?
YES - Check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and then go to "Verification of Vehicle Repair" procedure.
NO - Substitute with a known-good A/C-ECU and check for proper operation If the problem is corrected, replace A/C-ECU and then go to "Verification of Vehicle Repair" procedure.
VERIFICATION OF VEHICLE REPAIR
After a repair, it is essential to verifying that the fault has been corrected.
1. Connect scan tool and select "Diagnostic Trouble Codes (DTCs)" mode
2. Using scantool, Clear DTC.
3. Operate the vehicle within DTC Enable conditions in General information
4. Are any DTCs present?
YES - Go to the applicable troubleshooting procedure.
NO - System is performing to specification at this time.