B1238

DTC B1238 AMBIENT TEMPERATURE SENSOR OPEN (HIGH)

Component Location:

COMPONENT LOCATION

GENERAL DESCRIPTION
The ambient temperature senor located at the center stay of the condenser, detects ambient air temperature. It is a negative type thermistor whose resistance is inversely proportional to temperature. Its output is used for discharge temperature sensor, sensor fail-safe, temperature regulation door lock, blower motor level control, mix mode control and in-car humidity control.

DTC DESCRIPTION
The A/C controller sets DTC B1238 if there is an open circuit in ambient temp. sensor signal harness or the measured resistance value of sensor is more than threshold value (about 527 kohms)

DTC Detecting Condition:

DTC DETECTING CONDITION

Specification:

SPECIFICATION

MONITOR SCANTOOL DATA
1. Connect scantool to Data Link Connector (DLC).
2. Engine "ON"




3. Monitor the "AMBIENT TEMP SENSOR" Parameter on the Scantool.
* Parameter of "AMBIENT TEMP. SENSOR" will be fixed at 20 degrees C (67 degrees F), if there is any fault in AMBIENT TEMP SENSOR.

4. Are the DTC B1238 present and is parameter of "AMBIENT TEMP SENSOR" fixed?

YES - Go to "Inspection" procedure.

NO - Fault is intermittent caused by poor contact in the sensor's and/or A/C controller's connector or was repaired and A/C controller memory was not cleared. Thoroughly 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.

TERMINAL AND 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?

YES - Repair as necessary and go to "Verification of Vehicle Repair" procedure.

NO - Go to "Signal circuit inspection" procedure.

SIGNAL CIRCUIT INSPECTION
1. Check for open in harness.
1. Ignition "OFF"
2. Disconnect ambient temp. sensor.




3. Measure resistance between terminal "1" of ambient temp. sensor and terminal "3" of A/C Control Unit.

Specification : Approx. 0 ohms

4. Is the measured resistance within specifications?

YES - Go to "Ground circuit Inspection" procedure.

NO - Check for open in harness. Repair as necessary and go to "Verification of Vehicle Repair" procedure

GROUND CIRCUIT INSPECTION
1. Check for open in ground harness.
1. Ignition "OFF"
2. Disconnect ambient temp. sensor.




3. Measure resistance between terminal "2" of ambient temp. sensor and chassis ground

Specification : Approx. 0 ohms

4. Is the measured resistance within specifications?

YES - Go to "Component Inspection" procedure.

NO - Check for open in ground harness. Repair as necessary and go to "Verification of Vehicle Repair" procedure.

COMPONENT INSPECTION
1. Check Ambient temp. sensor.
1. Ignition "OFF"
2. Disconnect ambient temp. sensor.




3. Measure resistance between terminal "1" and "2" of ambient temp. sensor.

Specification : Refer the specifications in fig 3.

4. Is the measured resistance within specifications in fig3? (tolerance limits ± 3%)

YES - Go to "Check A/C Control Unit" procedure.

NO
- Substitute with a known-good ambient temp. sensor and check for proper operation.
- If the problem is corrected, replace ambient temp. sensor and then go to "Verification of Vehicle Repair" procedure.

2. Check A/C Control Unit
1. Engine "ON"
2. Disconnect ambient temp. sensor.




3. Measure voltage between terminal "3" of A/C Control Unit and chassis ground.

Specification : Approx. 5 V

4. Is the measured voltage within specifications?

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 Control Unit and check for proper operation.
- If the problem is corrected, replace A/C Control Unit and then go to "Verification of Vehicle Repair" procedure.

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?

YES - Go to the applicable troubleshooting procedure.

NO - System is performing to specification at this time.