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DTC B1031: Fin thermo sensor system (short circuit)
DTC B1032: Fin thermo sensor system (open 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 heater controller assembly (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 set as a past trouble, carry out diagnosis with particular emphasis on wiring and connector(s) between the heater controller assembly (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
  • The wiring harness or connectors may have loose, corroded, or damaged terminals, or terminals pushed back in the connector
  • Malfunction of the fin thermo sensor.
  • Malfunction of the heater controller assembly (A/C-ECU).
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB991223: Harness Set
  • MB992006: Extra Fine Probe
STEP 1. Using scan tool (M.U.T.-III), check data list.
(1)
cautionTo prevent damage to scan tool (M.U.T.-III), always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool (M.U.T.-III).
Connect scan tool (M.U.T.-III). Refer to "How to connect the Scan Tool (M.U.T.-III) ."
(2) Check that the following service data display contents are normal. (Refer to ).
Item No.20: Air thermo sensor
Is the check result normal?
Go to Step 4.
Go to Step 2.
 
STEP 2. Check of open and short circuit in + and - line between fin thermo sensor and auto heater controller assembly (A/C-ECU) connector.
Is the check result normal?
Go to Step 3.
Repair the connector(s) or wiring harness.
 
STEP 3. Check the fin thermo sensor.
Refer to .
Is the check result normal?
Go to Step 4.
Replace the fin thermo sensor (Refer to ).
 
STEP 4. Check whether the DTC is set again.
Is the DTC set?
Replace the heater controller assembly (A/C-ECU).
The trouble can be an intermittent malfunction (Refer to GROUP 00 - How to Cope with Intermittent Malfunction ).