VERACRUZ(EN) >2009 > G 3.8 DOHC > Heating,Ventilation, Air Conditioning > Troubleshooting>B1234 In-Car Temperature Sensor Open (High)  
Component Location

General Description
The incar temperature sensor joined to Humidity sensor as one body is located at heater control unit. It contains a thermistor which measures the temperature of the inside. The signal,decided by the resistance value which changes in accordance with perceived inside temperature, is delivered to heater control unit. According to this signal, the control unit regulates incar temperature to intended value.
DTC Description
The ECM sets DTC B1234 if there is an open circuit in incar temp sensor signal harness or the measured voltage value of the sensor is more than the threshold value(4.9V)
DTC Detecting Condition
Item
 Detecting Condition
 Possible Cause
DTC Strategy
•
Resistance check
•
Open Circuit in harness
•
Faulty incar temp.sensor
•
Faulty A/C Control Unit
Threshold value
•
>528kΩ
Detecting time
•
0.3sec
FAIL SAFE
•
Control with the value of 25°C

Signal Waveform And Data
※ Resistance value of incar temp sensor as a function of temperature.
Temperature(°C)
 Resistance(kΩ)
 Temperature(°C)
 Resistance(kΩ)
-20
 285.6
 20
 37.4
-10
 164.6
 30
 24.1
0
 97.7
 40
 15.9
10
 59.67
 50
 10.8

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?

▶ Go to " Inspection/Repair " procedure .

▶ 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, poorconnection, 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?

 ▶ Repair as necessary and go to "Verification of Vehicle Repair" procedure

 ▶ Go to "Signal circuit Open Inspection" procedure.

Signal Circuit Open Inspection
1.
Ignition "OFF"
2.
A/C-ECU, Incar temp.sensor : Disconnect.
3.
Measure resistance between Signal(+) terminal of Incar temp.sensor harness connector and Signal(+) terminal of A/C-ECU harness connector.
Specification : 1Ω below
4.
Is "resistance" display near the specified value?

 ▶ Go to "Sensor ground circuit Open Inspection " procedure.

 ▶ Check for open in harness.
▶ Repair as necessary and then go to "Verification of Vehicle Repair" procedure.

Sensor Ground Circuit Open Inspection
1.
Ignition "OFF"
2.
A/C-ECU, Incar temp.sensor : Disconnect.
3.
Measure resistance between Sensor ground(-) terminal of Incar temp.sensor harness connector and Sensor ground(-) terminal of A/C-ECU harness connector.
Specification : 1Ω below
4.
Is "resistance" display near the specified value?

 ▶ Go to " Component inspection " procedure .

 ▶ Check for open in harness.
▶ Repair as necessary and then go to "Verification of Vehicle Repair" procedure.

Component Inspection
Check Incar temp.sensor
1.
Ignition "OFF"
2.
A/C-ECU, Incar temp.sensor : Connect.
3.
Measure resistance between Signal(+) terminal of Incar temp.sensor harness connector and and Sensor ground harness connector .(Component side)
Specification : Refer the specifications in fig.1
Temperature(°C)
 Resistance(kΩ)
 Temperature(°C)
 Resistance(kΩ)
-20
 285.6
 20
 37.4
-10
 164.6
 30
 24.1
0
 97.7
 40
 15.9
10
 59.67
 50
 10.8

※ Specifications : Resistance value of incar 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?

 ▶ Go to "Check A/C-ECU" procedure

 ▶ Substitute with a known-good Incar temp.sensor and check for proper operation. If the problem is corrected, replace Incar temp.sensor and then go to "Verification of Vehicle Repair" procedure.

Check A/C-ECU
1.
Ignition "OFF"
2.
A/C-ECU : Connect, Incar temp.sensor : Disconnect.
3.
Ignition "ON"(ENGINE "OFF").
4.
Measure voltage between Signal(+) terminal of Incar temp.sensor harness connector and and chassis ground .(Component side)
Specification : approx. 5V
5.
Is "voltage" display near the specified value?

 ▶ 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.

 ▶ 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?

 ▶ Go to the applicable troubleshooting procedure.

 ▶ System is performing to specification at this time.