Troubleshooting

DTC P0115 Engine Coolant Temp. Circuit Malfunction

Figure 1:

Reference:

CIRCUIT DESCRIPTION
A thermistor built into the engine coolant temp. sensor changes the resistance value according to the engine coolant temp.
A thermistor built in 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 (See Fig. 1).
The engine coolant temperature sensor is connected to the ECM. The 5 V power source voltage in the ECM is applied to the engine coolant temperature sensor from the terminal THW via 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 temp. is assumed to be 80°C (176°F).





DETECTING CONDITION





HINT: After confirming DTC P0115 use the OBD II scan tool or TOYOTA hand-held tester to confirm the engine coolant temp. from "CURRENT DATA".





WIRING DIAGRAM

















INSPECTION PROCEDURE

HINT: If DTC P0110 (Intake Air Temp. Circuit Malfunction), P0115 (Engine Coolant Temp. Circuit Malfunction), P0120 (Throttle/Pedal/Position Sensor/Switch "A" Circuit Malfunction) and P1410 (EGR Valve Position Sensor Circuit Malfunction) are output simultaneously, E2 (Sensor Ground) may be open.