Code No. P0115: Engine Coolant Temperature Sensor System

OPERATION

• A power voltage of 5 V is applied to the engine coolant temperature sensor output terminal (terminal No. 1) from the engine-ECU <M/T> or engine-A/T-ECU <A/T> (terminal No. 98).
  
• The power voltage is earthed to the engine-ECU <M/T> or engine-A/T-ECU <A/T> (terminal No. 96) from the engine coolant temperature sensor (terminal No. 2).
  

FUNCTION

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

TROUBLE JUDGMENT

• 2 seconds later after the ignition switch has been in ON position or just after the engine has started up.
  

• The sensor output voltage is 4.6 V or more (water temperature of below -45°C or equivalent) for 4 seconds.
  

• The sensor output voltage is 0.1 V or less (water temperature of above 140°C or equivalent) for 4 seconds.
  

• After the engine has started up.
  

• The sensor output voltage rises 1.6 V or more (engine coolant temperature below 40°C or equivalent) from 1.6 V or less (engine coolant temperature above 40°C or equivalent).
  

PROBABLE CAUSE

• Failed engine coolant temperature sensor
  
• Open/short circuit in engine coolant temperature sensor circuit or loose connector contact
  
• Failed engine-ECU <M/T>
  
• Failed engine-A/T-ECU <A/T>
  

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

	Go to Step 2 .

Q. Is the check result normal? Go to Step 3 . Repair or replace.

Disconnect connector, and measure at sensor side. Resistance between terminal No. 1 and No. 2. OK: Engine coolant temperature at -20°C: 14 - 17 kΩ Engine coolant temperature at 0°C: 5.1 - 6.5 kΩ Engine coolant temperature at 20°C: 2.1 - 2.7 kΩ Engine coolant temperature at 40°C: 0.9 - 1.3 kΩ Engine coolant temperature at 60°C: 0.48 - 0.68 kΩ Engine coolant temperature at 80°C: 0.26 - 0.36 kΩ Q. Is the check result normal? Go to Step 4 . Replace engine coolant temperature sensor.

Disconnect connector and measure at harness side. Voltage between terminal No. 2 and earth. OK: 2 Ω or less Q. Is the check result normal? Go to Step 8 . Go to Step 5 .

Go to Step 6 . Repair or replace.

note Before checking harness, check intermediate connector C-116, and repair if necessary. Check earthing line for open circuit and damage. Q. Is the check result normal? Go to Step 7 . Repair.

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

	Replace engine-ECU <M/T> or engine-A/T-ECU <A/T>.

Disconnect connector, and measure at harness side. Ignition switch: ON Voltage between terminal No. 1 and earth. OK: 4.5 - 4.9 V Q. Is the check result normal? Go to Step 13 . Go to Step 9 .

Measure engine-ECU <M/T> or engine-A/T-ECU <A/T> terminal voltage. Disconnect B-08 engine coolant temperature sensor. Ignition switch: ON Voltage between terminal No. 98 and earth. OK: 4.5 - 4.9 V Q. Is the check result normal? Go to Step 10 . Go to Step 11 .

Q. Is the check result normal? Check and repair harness between B-08 (terminal No. 1) engine coolant temperature sensor connector and C-113 (terminal No. 98) engine-ECU <M/T> connector or engine-A/T-ECU <A/T> connector. Check output line for open circuit. Repair or replace.

Q. Is the check result normal? Go to Step 12 . Repair or replace.

Check output line for short circuit. Q. Is the check result normal? Go to Step 7 . Repair.

Use special tool test harness (MB991709) to connect connector, and measure at pick-up harness. Ignition switch: ON Voltage between terminal No. 1 and earth. OK: Engine coolant temperature at -20°C: 3.9 - 4.5 V Engine coolant temperature at 0°C: 3.2 - 3.8 V Engine coolant temperature at 20°C: 2.3 - 2.9 V Engine coolant temperature at 40°C: 1.3 - 1.9 V Engine coolant temperature at 60°C: 0.7 - 1.3 V Engine coolant temperature at 80°C: 0.3 - 0.9 V Q. Is the check result normal? Go to Step 7 . Go to Step 14 .

Q. Is the check result normal? Go to Step 15 . Repair or replace.

Check output line for damage. Q. Is the check result normal? Go to Step 7 . Repair.