Coolant Temperature Sensor
2021 Toyota RAV4 · 2.5L I4
Sensor Type
thermistor
Waveform Type
dc-variable
Location
Front of engine block, driver side near thermostat housing, threaded into coolant passage
Pins
2-pin connector
Timebase
1s/div for monitoring warmup
Voltage Scale
1V/div
Trigger
Not applicable, use DC coupling
Wiring
Brown wire (signal to ECM pin T24), Black wire (sensor ground)
Expected Voltage Range
At Idle
0.4V to 0.6V
At Higher RPM
0.3V to 0.5V
Expected Pattern
Steady DC voltage that decreases as temperature rises, NTC thermistor curve
Known-Good Waveform
Cold engine (68°F) shows 2.2-2.5V, dropping smoothly to 0.4-0.6V at normal operating temperature (195-205°F). Voltage should decrease steadily during warmup with no sudden jumps or dropouts, following the NTC thermistor resistance curve with 5V reference voltage from ECM.
Common Failure Patterns
Voltage stuck at 4.5-5V regardless of temperature
Cause: Open circuit in sensor or wiring, broken thermistor element
Voltage near 0V or erratic jumping between 0-5V
Cause: Short to ground in wiring harness or failed sensor with internal short
Voltage reads normal cold but drops too slowly during warmup
Cause: Contaminated sensor tip preventing proper thermal contact with coolant
Related DTCs: P0116
Diagnostic Tips
Compare voltage to actual coolant temperature with IR thermometer. ECM uses 5V pull-up with internal resistor, so open circuit reads high. Check connector terminals for corrosion which is common on this sensor location due to coolant migration.
Related Diagnostic Trouble Codes
P0115P0116P0117P0118P0119
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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