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DTC P0538: Fin Thermo Sensor Circuit High Input
 
 
 
 
CIRCUIT OPERATION
  • A power voltage of 5 V is applied to the fin thermo sensor connector terminal from the ECM connector terminal AC/T.
  • The power voltage is grounded to the ECM connector terminal ACTE from the fin thermo sensor connector terminal.
 
 
TECHNICAL DESCRIPTION
  • The fin thermo sensor converts the evaporator surface temperature into a voltage signal, and sends the voltage to the ECM.
  • In response to the signal, the ECM controls the A/C compressor relay.
  • The fin thermo sensor is a kind of resistor, which has characteristics to reduce its resistance as air temperature rises. Therefore, the sensor output voltage varies with the air temperature, and becomes lower as the air temperature rises.
 
 
DTC SET CONDITIONS
Check Condition
  • After 2 seconds since the ignition switch is turned ON or since the completion of engine start.
Judgment Criterion
  • Fin thermo sensor output voltage is more than 4.9 V for 4 seconds.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • Control as if the evaporator surface temperature is -6.4°C.
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be stored are:)
  • Failed fin thermo sensor
  • Open circuit or harness damage in fin thermo sensor circuit or loose connector contact
  • Failed ECM
 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: Vehicles Communication Interface (V.C.I.)
    • MB991827: M.U.T.-III USB Cable
    • MB991910: M.U.T.-III Main Harness A (Vehicles with CAN communication system)
STEP 1. Using scan tool (M.U.T.-III), check data list.
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).
(1) Connect scan tool (M.U.T-III). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-III) .
(2) Turn the ignition switch to the "ON" position.
(3) Check the following item in the data list. Refer to Data List Reference Table .
  1. Item 174: Fin Thermo sensor
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
Go to Step 2.
 
STEP 2. Check the fin thermo sensor.
Refer to Fin Thermo Sensor Check (Refer to GROUP 55A - Heater Unit and Blower Assembly - Inspection - Fin Thermo Sensor Check ).
Is the sensor operating properly?
Go to Step 3.
Replace the fin thermo sensor. Then go to Step 9.
 
STEP 3. Measure the resistance at fin thermo sensor connector.
(1) Disconnect the connector and measure at the harness side.
(2) Measure the voltage between terminal ACTE line and ground.
  • Continuity (2 ohms or less)
Does continuity exist?
Go to Step 6.
Go to Step 4.
 
STEP 4. Check of open circuit and damage in ACTE line between fin thermo sensor connector and ECM connector.
Is the check result normal?
Go to Step 5.
Repair the connector(s) or wiring harness. Then go to Step 9.
 
STEP 5. Using scan tool (M.U.T.-III), check data list.
(1) Turn the ignition switch to the "ON" position.
(2) Check the following item in the data list. Refer to Data List Reference Table .
  1. Item 174: Fin Thermo sensor
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions .
Replace the ECM. Then go to Step 9.
 
STEP 6. Measure the voltage at fin thermo sensor connector.
(1) Disconnect the connector and measure at the harness side.
(2) Turn the ignition switch to the "ON" position.
(3) Measure the voltage between terminal AC/T line and ground.
  • Voltage should be between 4.5 and 4.9 volts.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the measured voltage between 4.5 and 4.9 volts?
Go to Step 8.
Go to Step 7.
 
STEP 7. Check of open circuit in AC/T line between fin thermo sensor connector and ECM connector.
Is the check result normal?
Go to Step 5.
Repair the connector(s) or wiring harness. Then go to Step 9.
 
STEP 8. Check of damage in AC/T line between fin thermo sensor connector and ECM connector.
Is the check result normal?
Go to Step 5.
Repair the connector(s) or wiring harness. Then go to Step 9.
 
STEP 9. Using scan tool (M.U.T.-III), check data list.
(1) Turn the ignition switch to the "ON" position.
(2) Check the following item in the data list. Refer to Data List Reference Table .
  1. Item 174: Fin Thermo sensor
(3) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
The inspection is complete.
Retry the troubleshooting.