Code No. P0712: Transmission Oil Temperature Sensor Low <M/T>

OPERATION

A power voltage of 5 V is applied to the transmission oil temperature sensor output terminal from the engine-ECU connector terminal ATS2.
The power voltage is earthed to the engine-ECU connector terminal ATS2E from the transmission oil temperature sensor connector terminal.

FUNCTION

The transmission oil temperature sensor converts the transmission oil temperature into a voltage signal, and inputs the voltage to the engine-ECU.
In response to the signal, the engine-ECU controls the fuel infection amount and the fast idle speed when the engine is cold state.
The transmission oil temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the transmission oil temperature rises. Therefore, the sensor output voltage varies with the transmission oil temperature, and becomes lower as the transmission oil temperature rises.

TROUBLE JUDGEMENT

Check Conditions

Battery positive voltage is 8 - 16 V
2 seconds later after the ignition switch has been in "ON" position or the engine has started up.

Judgement Criterion

The transmission oil temperature sensor output voltage is 0.15 V or less.

FAIL-SAFE AND BACKUP FUNCTION

The transmission oil temperature is controlled to be 140°C (Start-up of -25°C)
The EGR control is stopped (fully closed).
The throttle valve is opened (Electrical discontinuity).
The DPF regeneration is prohibited.

PROBABLE CAUSES

Failed transmission oil temperature sensor
Short circuit in transmission oil temperature sensor circuit or loose connector contact
Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. Perform resistance measurement at transmission oil temperature sensor connector.

Transmission oil temperature sensor connector check.
Disconnect connector, and measure at sensor side.
Resistance between terminals.

OK:
Transmission oil temperature at -20°C: 14 - 17 kΩ
(Transmission oil temperature at 0°C: 5.1 - 6.5 kΩ)
Transmission oil temperature at 20°C: 2.1 - 2.7 kΩ
(Transmission oil temperature at 40°C: 0.9 - 1.3 kΩ)
(Transmission oil temperature at 60°C: 0.48 - 0.68 kΩ)
(Transmission oil temperature at 80°C: 0.26 - 0.36 kΩ)

Q. Is the check result normal?

	Go to Step 2.

	Repair or replace the connector, or replace the transmission oil temperature sensor.

STEP 2. Perform voltage measurement at transmission oil temperature sensor connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal engine-ECU ATS2 line and body earth.

OK: 4.5 - 4.9 V

Q. Is the check result normal?

	Go to Step 5.

	Go to Step 3.

STEP 3. Check harness between transmission oil temperature sensor connector terminal and engine-ECU connector terminal ATS2.

Check output line for short circuit.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 4. M.U.T.-III diagnosis code

Reconfirmation of diagnosis code.

Q. Is the diagnosis code set?

	Replace the engine-ECU.

	Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions).

STEP 5. Perform resistance measurement at transmission oil temperature sensor connector.

Disconnect connector, and measure at harness side.
Resistance between terminal engine-ECU ATS2E line and body earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

	Go to Step 7.

	Go to Step 6.

STEP 6. Check harness between transmission oil temperature sensor connector terminal and engine-ECU connector terminal ATS2E.

Check earthing line for damage.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Check harness between transmission oil temperature sensor connector terminal and engine-ECU connector terminal ATS2.

Check output line for damage.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.