3.
Monitor the "EVAPORATIVE SENSOR" Parameter on the Scantool.
The Evaporator temperature sensor located on heater unit, detects the core temperature and interrupts compressor relay power, in order to prevent evaporator freezing by excessive cooling. It is a negative type thermistor whose resistance is inversely proportional to temperature.
The A/C controller sets DTC B1242 if there is an open circuit in evaporator temp. sensor signal harness or the measured resistance value of sensor is more than threshold value(about 13.6kΩ)
Item | Detecting Condition | Possible cause |
DTC Strategy | ● Resistance check | ● Open Circuit in harness ● Faulty Evaporator temp. Sensor ● Faulty A/C control unit |
Threshold value | ● ＞ 13.6kΩ | |
Detecting time | ● 0.3 sec | |
FAIL SAFE | ● Control with the value of -2°C(28.4°F) |
Temperature[°C(°F)] | Resistance(kΩ) | Temperature[°C(°F)] | Resistance(kΩ) |
-10(14) | 13.6 | 15(59) | 3.9 |
0(32) | 8 | 30(86) | 2 |
5(41) | 6.2 | 40(104) | 1.3 |
10(50) | 4.9 | 50(122) | 0.9 |
Connect scantool to Data Link Connector(DLC).
Engine "ON"
Monitor the "EVAPORATIVE SENSOR" Parameter on the Scantool.
Are the DTC B1242 present and is parameter of "EVAPORATIVE SENSOR" fixed?
※ Parameter of "EVAPORATIVE SENSOR" will be fixed at -2℃(28.4℉), if there is any fault in EVAPORATIVE SENSOR.
Go to "Inspection" procedure.
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.
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.
Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage.
Has a problem been found?
Repair as necessary and go to "Verification of Vehicle Repair" procedure.
Go to "Signal circuit inspection" procedure.
Check for open in harness.
Ignition "OFF"
Disconnect evaporator temp. sensor.
Measure resistance between terminal "1" of evaporator temp. sensor and terminal "6" of A/C Control Unit.
Specification : Approx. 0 Ω
Is the measured resistance within specifications?
Go to "Ground circuit Inspection " procedure.
Check for open in harness. Repair as necessary and go to "Verification of Vehicle Repair" procedure.
Check for open in ground harness.
Ignition "OFF"
Disconnect evaporator temp. sensor.
Measure resistance between terminal "2" of evaporator temp. sensor and chassis ground.
Specification : Approx. 0 Ω
Is the measured resistance within specifications?
Go to "Component Inspection " procedure.
Check for open in harness. Repair as necessary and go to "Verification of Vehicle Repair" procedure.
Check evaporator temp. sensor.
Ignition "OFF"
Disconnect evaporator temp. sensor.
Measure resistance between terminal "1" and "2" of evaporator temp. sensor.
Specification : Refer the specifications in fig 3.
Is the measured resistance within specifications in fig3? (tolerance limits ±3%)
Go to "Check A/C Control Unit" procedure.
Substitute with a known-good evaporator temp. sensor and check for proper operation.
If the problem is corrected, replace evaporator temp. sensor and then go to "Verification of Vehicle Repair" procedure.
Check A/C Control Unit
Engine "ON"
Disconnect evaporator temp. sensor.
Measure voltage between terminal "6" of A/C Control Unit and chassis ground.
Specification : Approx. 5V
Is the measured voltage within specifications?
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 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.
After a repair, it is essential to verify that the fault has been corrected.
Connect scantool and select "Diagnostic Trouble Codes(DTCs)" mode and then clear DTC.
Operate the vehicle and monitor the DTC on the scantool.
Are any DTCs present?
Go to the applicable troubleshooting procedure.
System is performing to specification at this time.
