Troubleshooting

DTC P0115 ENGINE COOLANT TEMPERATURE CIRCUIT MALFUNCTION





CIRCUIT DESCRIPTION
A thermistor built into the engine coolant temperature sensor changes the resistance value according to the engine coolant temperature.
The structure of the sensor and connection to the ECM is the same as in the intake air temperature circuit malfunction shown on DTC P0110 Intake Air Temp. Circuit Malfunction.
The intake air temperature sensor is built into mass air flow meter and senses the intake air temperature.
A thermistor built in the sensor changes the resistance value according to the intake air temperature.
The lower the intake air temperature, the greater the thermistor resistance value, and the higher the intake air temperature, the lower the thermistor resistance value (See Fig. 1).
The intake air temperature sensor is connected to the ECM. The 5 V power source voltage in the ECM is applied to the intake air temperature sensor from terminal THA via resistor R. That is, resistor R and the intake air temperature sensor are connected in series. When the resistance value of the intake air temperature sensor changes in accordance with changes in the intake air temperature, the potential at terminal THA 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 (176 °F).




DETECTING CONDITIONS






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




WIRING DIAGRAM
















INSPECTION PROCEDURE

HINT:
- If DTCs P0110, PO115, P0120 and P1410 are output simultaneously, E2 (sensor ground) may be open.
- Read freeze frame data using LEXUS hand-held tester or OBD II scan tool. Because freeze frame records the engine conditions when the malfunction is detected. When troubleshooting, it is useful for determining whether the vehicle was running or stopped, the engine was warmed up or not, the air-fuel ratio was lean or rich etc. at the time of the malfunction.