Toyota Celica 2005 Repair Manual page 581

DI−382
DTC P0115
DTC P0117
DTC P0118
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 the DTC P0115, it operates fail safe function in which the engine coolant temperature
is assumed to be 80°C (176°F).
DTC No. Proceed to
P0115 Step 1
P0117 Step 4
P0118 Step 2
HINT:
After confirming DTC "P0115, P0117 or P0118", 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.
Displayed Temperature
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 resistance varies as output voltage from the sensor changes.
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.
2005 CELICA (RM1131U)
DIAGNOSTICS
Engine Coolant Temperature Circuit
Engine Coolant Temperature Circuit Low
Input
Engine Coolant Temperature Circuit High
Input
DTC Detection Condition
Open or short in engine cool-
ant temperature sensor circuit
for 0.5 sec.
Short in engine coolant tem-
perature sensor circuit for 0.5
sec.
Open in engine coolant tem-
perature sensor circuit for 0.5
sec.
−40°C (−40°F)
− ENGINE (2ZZ−GE)
S Open or short in engine coolant temperature sensor circuit
S Engine coolant temperature sensor
S ECM
580
Trouble Area
Malfunction
Open circuit
Short circuit
DI380−18