Toyota Celica 2005 Repair Manual page 286

DTC P0115
CIRCUIT DESCRIPTION
A thermistor is built into the Engine Coolant Temperature (ECT) sensor and changes the resistance value
according to the engine coolant temperature.
The structure of the sensor and connection to the ECM are the same as the Intake Air Temperature (IAT)
sensor.
HINT:
If the ECM detects DTC P0115, it operates fail safe function in which the engine coolant temperature is as-
sumed to be 80°C (176°F).
DTC No.
P0115 Open or short in engine coolant temperature sensor circuit
HINT:
After confirming DTC "P0115", use the OBD II scan tool or the hand−held tester to confirm the engine coolant
temperature from the DIAGNOSIS / ENHANCED OBD II / DATA LIST / ALL.
140°C (284°F) or more
MONITOR DESCRIPTION
The ECT (Engine Coolant Temperature) sensor is used to monitor the engine coolant temperature. The ECT
sensor has a thermistor that varies its resistance depending on the temperature of the engine coolant. When
the coolant temperature is low, the resistance in the thermistor increases. When the temperature is high, the
resistance drops. The variations in resistance are reflected in the voltage output from the sensor.
The ECM monitors the sensor voltage and uses this value to calculate the engine coolant temperature.
When the sensor output voltage deviates from the normal operating range, the ECM interprets this as a fault
in the ECT sensor and sets a DTC.
Example:
When the ECM calculates that the ECT is less than −40_C (−40_F), or more than 140_C (284_F), and if either
condition continues for 0.5. sec. or more, the ECM will set a DTC.
MONITOR STRATEGY
Related DTCs
Required sensors/components
Frequency of operation
Duration
MIL operation
Sequence of operation
2005 CELICA (RM1131U)
DIAGNOSTICS
Engine Coolant Temperature Circuit
Detection Item
Temp. Displayed
−40°C (−40°F)
Engine coolant temperature sensor
Continuous
0.5 sec.
Immediate
None
− ENGINE (1ZZ−FE)
S Open or short in engine coolant temperature sensor circuit
S Engine coolant temperature sensor
S ECM
P0115
285
Trouble Area
Malfunction
Open circuit
Short circuit
Engine coolant temperature sensor range check
(Fluttering)
Engine coolant temperature sensor range check
(Low voltage)
Engine coolant temperature sensor range check
(High voltage)
DI−87
DI380−17