Automatic Air Conditioning

DTC B1022: Air Thermo Sensor System (Open Circuit)














FUNCTION

The air thermo sensor sends the temperature information inside the heater unit to the A/C-ECU and controls the temperature of the air coming out of the vents.

DETECTION LOGIC

This code is set when the air thermo sensor circuit is open (power supply side and ground side).

PROBABLE CAUSES

- Malfunction of connector.
- Malfunction of the harness.
- Malfunction of the air thermo sensor.
- Malfunction of the A/C-ECU.

DIAGNOSIS

Required Special Tools:

- MB991223: Harness Set
- MB992006: Extra Fine Probe
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: M.U.T.-III USB Cable
- MB991910: M.U.T.-III Main Harness A

STEP 1. Using scan tool MB991958, check data list.





(1)
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.

Connect scan tool MB991958 to the data link connector.
(2)Start the engine.
(3)Set scan tool MB991958 to the data reading mode.

- Item 20: air thermo sensor
- Check that the temperature behind the evaporator matches the displayed value on the scan tool.

NOTE:
When this DTC is set and the system is in fail-safe status, the value of service data displays -6°C (28°F).

(4)Turn the ignition switch to the "LOCK" (OFF) position.

Q. Is the sensor within the specified range?

YES Go to Step 2.

NO Go to Step 3.

STEP 2. Recheck for diagnostic trouble code.

Recheck if the DTC is set.

(1)Erase the DTC.

(2)Turn the ignition switch to "OFF" position.

(3)Turn the ignition switch to "ON" position.

(4)Drive the vehicle and check that the diagnostic trouble code is not set.

Q. Is the check result satisfactory?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.
NO Replace the A/C-ECU.
STEP 3. Check air thermo sensor connector C-102 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Is air thermo sensor connector C-102 in good condition?

YES Go to Step 4.

NO Repair or replace the connector. Harness Connector Inspection.

STEP 4. Check the air thermo sensor.





(1)Disconnect the air thermo sensor connector C-102.





(2)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 air thermo sensor in good condition?

YES Go to Step 5.

NO Replace the air thermo sensor.

STEP 5. Check A/C-ECU connector C-15 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Is A/C-ECU connector C-15 in good condition?

YES Go to Step 6.

NO Repair or replace the connector. Harness Connector Inspection.

STEP 6. Check the wiring harness for open circuit.









(1)Disconnect A/C-ECU connector C-20 and air thermo sensor connector C-102, and measure the resistance at the wiring harness side.





(2)Measure the resistance between A/C-ECU connector C-20 terminal 24 and air thermo sensor connector C-102 terminal 1.
OK: Less than 2 ohms

Q. Is the check result normal?

YES Go to Step 8.

NO Go to Step 7.

STEP 7. Check the wiring harness between A/C-ECU connector C-20 (terminal 24) and air thermo sensor connector C-102 (terminal 1).









Q. Is the wiring harness between A/C-ECU connector C-20 (terminal 24) and air thermo sensor connector C-102 (terminal 1) in good condition?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.

NO Repair the wiring harness.

STEP 8. Check the wiring harness for open circuit.









(1)Disconnect A/C-ECU connector C-15 and air thermo sensor connector C-102, and measure the resistance at the wiring harness side.





(2)Measure the resistance between A/C-ECU connector C-15 terminal 20 and air thermo sensor connector C-102 terminal 2.
OK: Less than 2 ohms

Q. Is the check result normal?

YES Go to Step 10.

NO Go to Step 9.

STEP 9. Check the wiring harness between A/C-ECU connector C-15 (terminal 20) and air thermo sensor connector C-102 (terminal 2).









Q. Is the wiring harness between A/C-ECU connector C-15 (terminal 20) and air thermo sensor connector C-102 (terminal 2) in good condition?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.

NO Repair the wiring harness.

STEP 10. Recheck for diagnostic trouble code.

Recheck if the DTC is set.

(1)Erase the DTC.

(2)Turn the ignition switch to "OFF" position.

(3)Turn the ignition switch to "ON" position.

(4)Drive the vehicle and check that the diagnostic trouble code is not set.

Q. Is the check result satisfactory?

YES It can be assumed that this malfunction is intermittent. How to Cope With Intermittent Malfunctions.
NO Replace the A/C-ECU.