Code No. P0712: Transmission fluid Temperature Sensor Low <Vehicles with M/T>

OPERATION

A power voltage of 5 V is applied to the transmission fluid 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 fluid temperature sensor connector terminal.

FUNCTION

The transmission fluid temperature sensor converts the transmission fluid 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 fluid temperature sensor is a kind of resistor, which has characteristics to reduce its resistance as the transmission fluid temperature rises. Therefore, the sensor output voltage varies with the transmission fluid temperature, and becomes lower as the transmission fluid 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 fluid temperature sensor output voltage is 0.15 V or less.

FAIL-SAFE AND BACKUP FUNCTION

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

DIAGNOSIS PROCEDURE

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

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

OK:
Transmission fluid temperature at -20°C: 14 - 17 kΩ
(Transmission fluid temperature at 0°C: 5.1 - 6.5 kΩ)
Transmission fluid temperature at 20°C: 2.1 - 2.7 kΩ
(Transmission fluid temperature at 40°C: 0.9 - 1.3 kΩ)
(Transmission fluid temperature at 60°C: 0.48 - 0.68 kΩ)
(Transmission fluid 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 fluid temperature sensor.

STEP 2. Perform voltage measurement at transmission fluid 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 fluid 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 fluid 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 fluid 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 fluid 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.