Fin Thermo Sensor System
DTC B1031, B1032: Fin Thermo Sensor SystemFin Thermo Sensor Circuit:
DTC SET CONDITION
- DTC B1031 is set if there is a short circuit in the fin thermo sensor input circuit.
- DTC B1032 is set if there is a defective connector connection, or if there is an open circuit in the harness.
TECHNICAL DESCRIPTION (COMMENT)
Current trouble
- The A/C-ECU, the fin thermo sensor, or connector(s) or wiring between the two may be defective.
Past trouble
- If DTC B1031 or B1032 is stored as a past trouble, carry out diagnosis with particular emphasis on wiring and connector(s) between the A/C-ECU and the fin thermo sensor. If the connectors and wiring are normal, and obviously the ECU is the cause of the trouble, replace the ECU. If in doubt, do not replace the ECU.
TROUBLESHOOTING HINT
- Malfunction of connector.
- Malfunction of the harness.
- Malfunction of the fin thermo sensor.
- Malfunction of the A/C-ECU.
DIAGNOSIS
Required Special Tool:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: Vehicle Communication Interface (V.C.I.)
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A
STEP 1. Using scan tool MB991958, diagnose the CAN bus line
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
1. Connect scan tool MB991958. Refer to "How to connect the Scan Tool (M.U.T.-III)." How to Connect the Scan Tool (M.U.T.-III)
2. Turn the ignition switch to the "ON" position.
3. Diagnose the CAN bus line.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the CAN bus line found to be normal?
YES : Go to Step 2.
NO : Repair the CAN bus line.
STEP 2. Recheck for diagnostic trouble code.
Recheck if the DTC is set
1. Erase the DTC.
2. Turn the ignition switch to "ON" position
3. Check if the DTC is set.
Q: Is the DTC set?
YES : Go to Step 3.
NO : It can be assumed that this malfunction is intermittent.
STEP 3. Check fin thermo sensor connector C-113 and A/C-ECU connector C-20 for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Q: Are fin thermo sensor connector C-113 and A/C-ECU connector C-20 in good condition?
YES : Go to Step 4.
NO : Repair or replace the connector.
STEP 4. Check the wiring harness between A/C-ECU connector C-20 (terminals 22 and 21) and fin thermo sensor connector C-113 (terminals 1 and 2).
- Check the sensor signal line and ground line for open and short circuit.
Q: Is the wiring harness between A/C-ECU connector C-20 (terminals 22 and 21) and fin thermo sensor connector C-113 (terminals 1 and 2) in good condition?
YES : Go to Step 5.
NO : Repair the wiring harness.
STEP 5. Check the fin thermo sensor.
Measure the resistance between connector terminals 1 and 2 under at least two different temperatures. The resistance values should generally match those in the graph.
NOTE: The temperature at the check should not exceed the range in the graph.
Q: Is the fin thermo sensor in good condition?
YES : Replace the A/C-ECU. Then go to Step 6.
NO : Replace the fin thermo sensor. Then go to Step 6.
STEP 6. Recheck for diagnostic trouble code.
Check again if the DTC is set.
1. Connect scan tool MB991958 to the data link connector (2) Turn the ignition switch to the "ON" position.
3. Check if the DTC is set.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the DTC set?
YES : Return to Step 1.
NO : The procedure is complete.