Code No. P0117: Engine Coolant Temperature Sensor Circuit Low Input

OPERATION

• A power voltage of 5 V is applied to the engine coolant temperature sensor power terminal from the engine-ECU connector terminal WTS.
  
• The power voltage is earthed to the engine-ECU connector terminal WTSE from the engine coolant temperature sensor connector terminal.
  

FUNCTION

• The engine coolant temperature sensor converts the engine coolant temperature into a voltage signal, and inputs the voltage to the engine-ECU.
  
• In response to the signal, the engine-ECU controls the fuel injection 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 JUDGEMENT

• More than 2 seconds have passed since the engine starting sequence was completed.
  

• Engine coolant temperature sensor output voltage is less than 0.1 V (corresponding to an engine coolant temperature of 140°C or more) for 2 seconds.
  

FAIL-SAFE AND BACKUP FUNCTION

• Control as if the engine coolant temperature is 80°C.
  

PROBABLE CAUSES

• Failed engine coolant temperature sensor
  
• Short circuit in engine coolant temperature sensor circuit or loose connector contact
  
• Failed engine-ECU
  

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

	Go to Step 2.

	Go to Step 3.

	Repair or replace the connector, or replace the engine coolant temperature sensor.

	Go to Step 5.

	Go to Step 4.

	Go to Step 5.

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

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

	Replace the engine-ECU.