Coolant Temperature Sensor
2021 Honda Civic · 1.5L I4 Turbo
Sensor Type
thermistor
Waveform Type
dc-variable
Location
Driver's side of engine block, near thermostat housing, below throttle body on cylinder head
Pins
2-pin connector
Timebase
500ms/div
Voltage Scale
1V/div
Trigger
Free run or 2.5V
Wiring
Yellow/Green (signal) and Green/White (ground)
Expected Voltage Range
At Idle
0.4V to 0.6V
At Higher RPM
0.3V to 0.5V
Expected Pattern
Smooth DC voltage that decreases as temperature increases, negative temperature coefficient thermistor
Known-Good Waveform
At cold start (68°F), expect approximately 2.3-2.8V. As engine warms to operating temperature (195°F), voltage should smoothly decline to 0.4-0.6V. Voltage should be stable with no erratic jumps or dropouts during warm-up phase.
Common Failure Patterns
Voltage stuck at 4.8-5.0V regardless of temperature
Cause: Open circuit in sensor or wiring harness
Voltage reads near 0V or fluctuates erratically
Cause: Short to ground or contaminated connector
Voltage changes in steps or spikes randomly
Cause: Internal sensor resistance degradation or corroded terminals
Related DTCs: P0116
Diagnostic Tips
Honda ECTs are prone to connector corrosion due to proximity to coolant. Verify resistance at various temperatures: 68°F = 2.5kΩ, 176°F = 300Ω, 212°F = 177Ω. Check for coolant intrusion in connector.
Related Diagnostic Trouble Codes
P0115P0116P0117P0118P0119
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
Free, no signup. View all waveforms for this vehicle