Automatic Air Conditioning

DTC B1011: Ambient Air Temperature Sensor System (Short Circuit)














FUNCTION

The ambient air temperature sensor has characteristics that the resistance drops when the temperature rises, and it sends the temperature information outside the vehicle to the A/C-ECU to control the temperature.

DETECTION LOGIC

This code is set when the ambient air temperature sensor circuit (power supply side) is shorted to ground.

PROBABLE CAUSES

- Malfunction of connector.
- Malfunction of the harness.
- Malfunction of the ambient air temperature 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 02: Ambient air temperature sensor
- Check that the ambient temperature 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 20°C (68°F).

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

Q. Does the interior temperature match the displayed value on the scan tool?

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 ambient air temperature sensor connector A-28 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Is ambient air temperature sensor connector A-28 in good condition?

YES Go to Step 4.

NO Repair or replace the connector. Harness Connector Inspection.

STEP 4. Check the ambient air temperature sensor.





(1)Disconnect ambient air temperature sensor connector A-28.





(2)Measure the resistance between the sensor terminals under at least two temperatures. The resistance values should meet the values shown.
NOTE:
The temperature should be within the shown range.

Q. Is the ambient air temperature sensor in good condition?

YES Go to Step 5.

NO Replace the ambient air temperature sensor.

STEP 5. Check A/C-ECU connector C-20 for loose, corroded or damaged terminals, or terminals pushed back in the connector.





Q. Is A/C-ECU connectors C-20 in good condition?

YES Go to Step 6.

NO Repair or replace the connector. Harness Connector Inspection.

STEP 6. Measure the resistance at A/C-ECU connector C-20.





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





(2)Measure the resistance value between terminal 23 and ground.
OK: 1kohms or more

Q. Does the measured resistance value correspond with this range?

YES Go to Step 8.

NO Go to Step 7.

STEP 7. Check the wiring harness between A/C-ECU connector C-20 (terminal 23) and ambient air temperature sensor connector A-28 (terminal 2).









NOTE:
Also check intermediate connector C-21 for loose, corroded, or damaged terminals, or terminals pushed back in the connector. If intermediate connector C-21 is damaged, repair or replace the connector as described in Harness Connector Inspection Harness Connector Inspection.

Q. Is the wiring harness between A/C-ECU connector C-20 (terminal 23) and ambient air temperature sensor connector A-28 (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 8. 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.