Troubleshooting

DTC P0115 Engine Coolant Temp. Circuit Malfunction

CIRCUIT DESCRIPTION
A thermistor built into the engine coolant temperature sensor changes the resistance value according to the engine coolant temperature.
The sensor changes the resistance value according to the engine coolant temperature.
The lower the engine coolant temperature, the greater the thermistor resistance value, and the higher the engine coolant temperature, the lower the thermistor resistance value.
The engine coolant temperature sensor is connected to the ECM (See the Wiring Diagram below). The 5 volt power source voltage in the ECM is applied to the engine coolant temperature sensor from the terminal THW via a resistor R.
That is, the resistor R and the engine coolant temperature sensor are connected in series. When the resistance value of the engine coolant temperature sensor changes in accordance with changes in the engine coolant temperature, the potential at terminal THW also changes. Based on this signal, the ECM increases the fuel injection volume to improve driveability during cold engine operation.
If the ECM detects the DTC P0115, it operates the fail safe function in which the engine coolant temperature is assumed to be 80°C (l76°F).

DETECTING CONDITION



HINT: After confirming DTC P0115 use the OBDII scan tool or Toyota hand-held tester to confirm the engine coolant temperature from "CURRENT DATA".





WIRING DIAGRAM





INSPECTION PROCEDURE

HINT: If DTC "P0110" (engine coolant temp. circuit malfunction), "P0115" (engine coolant temp. circuit malfunction), "P0120" (throttle/pedal position sensor/switch "A" circuit malfunction) are output simultaneously, E2 (sensor ground) may be open.

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