B1241

B1241

Component Location:

General Description
The Evaporator sensor located on heater unit detects the core temperature. It is a negative type thermistor whose resistance is inversely proportional to temperature. Evaporator sensor transforms measured temperature into voltage value and delivers it to A/C ECU. when core temperature is blow threshold value, A/C ECU interrupts compressor relay power, in order to prevent evaporator freezing by excessive cooling.

DTC Description
The ECM sets DTC B1241 if there is a short circuit in evaporator sensor signal harness or the measured voltage value of the sensor is less than the threshold value (0.1 V)

DTC Detecting Condition:

Schematic Diagram:

Signal Waveform:

Monitor Scantool Data
1. Connect scantool to Data Link Connector (DLC).
2. Engine "ON".
3. Monitor the "EVAPORATIVE SENSOR" Parameter on the Scantool.






4. Are the DTC B1241 present and is parameter of "EVAPORATIVE SENSOR" fixed?
- Parameter of "EVAPORATIVE SENSOR" will be fixed at 28.4 °F, if there is any fault in EVAPORATIVE SENSOR.

YES
a. Go to "Inspection & Repair" procedure.

NO
a. Fault is intermittent caused by poor contact in the sensor's and/or A/C control unit's connector or was repaired and A/C control unit 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
a. Repair as necessary and go to "Verification Vehicle Repair" procedure.

NO
a. Go to "W/Harness Inspection" procedure.

Signal Circuit Inspection
1. Check for short to ground in harness
1. Ignition "OFF".
2. Disconnect evaporator sensor.
3. Measure resistance between terminal "1" of evaporator sensor and chassis ground.

Specification : Approx. Infinite ohms






4. Is the measured resistance within specifications?

YES
a. Go to "Component Inspection" procedure.

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

Component Inspection
1. Check evaporator sensor
1. Ignition "OFF".
2. Disconnect evaporator sensor.
3. Measure resistance between terminal "1" and "2" of evaporator sensor.

Specification : Refer the specifications in fig 3)









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

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

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

2. Check A/C Control Unit
5. Engine : "ON"
6. Disconnect evaporator sensor.
7. Measure voltage between terminal "4" of A/C Control Unit and chassis ground.

Specification : Approx. 5 V






8. Is the measured voltage within specifications?

YES
a. 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
a. 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
a. Go to the applicable troubleshooting procedure.

NO
a. System is performing to specification at this time.