Coolant Temperature Sensor
2021 Honda Accord · 1.5L I4 Turbo
Sensor Type
thermistor
Waveform Type
dc-variable
Location
Front of engine block, below throttle body, threaded into coolant passage near thermostat housing
Pins
2-pin connector
Timebase
1s/div or 5s/div for monitoring warm-up
Voltage Scale
1V/div
Trigger
Not applicable for DC monitoring
Wiring
Yellow/Green (signal wire to ECM pin A23) and Green/White (sensor ground)
Expected Voltage Range
At Idle
0.4V to 0.7V
At Higher RPM
0.3V to 0.6V
Expected Pattern
Smooth DC voltage that decreases as temperature increases, typical NTC thermistor with 5V reference
Known-Good Waveform
Cold engine (68°F) should read 2.3-2.7V. Normal operating temperature (195-205°F) reads 0.4-0.7V. Voltage should transition smoothly during warm-up over 5-8 minutes with no sudden jumps or dropouts. ECM uses this for fuel enrichment, cooling fan control, and turbo boost mapping.
Common Failure Patterns
Voltage stuck at 4.8-5.0V regardless of engine temperature
Cause: Open circuit in sensor element or wiring harness, broken wire at connector
Voltage reads 0V or near 0V constantly
Cause: Short to ground in wiring or internally shorted sensor element
Related DTCs: P0117
Diagnostic Tips
Honda turbocharged engines are sensitive to ECT input for boost control - inaccurate readings cause reduced power. Check connector for coolant intrusion which is common on this engine. Verify resistance: 2.2-2.7kΩ at 68°F, 200-400Ω at 195°F.
Related Diagnostic Trouble Codes
P0115P0116P0117P0118P0119
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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