Mass Airflow Sensor
2021 Honda Civic · 1.5L I4 Turbo
Sensor Type
thermistor
Waveform Type
dc-variable
Location
Intake air duct between air filter box and turbocharger compressor inlet
Pins
5-pin connector
Timebase
500ms/div
Voltage Scale
1V/div
Trigger
2.5V, center screen
Wiring
Yellow/Red (12V power), Green/Black (signal output), Black (sensor ground), Pink/Black (intake air temp signal), Black (IAT ground)
Expected Voltage Range
At Idle
1.2V to 1.8V
At Higher RPM
3.5V to 4.5V
Expected Pattern
Smooth analog voltage that increases linearly with airflow, minimal ripple or noise
Known-Good Waveform
At idle, MAF output should read 1.2-1.8V (approximately 3-6 g/s airflow). Under acceleration, voltage should rise smoothly without steps or dropouts to 3.5-4.5V at higher RPM and load. Signal should be clean with less than 50mV ripple; any sudden steps or glitches indicate contamination or failing hot-wire element. Voltage should correlate directly with calculated load displayed on scan tool.
Common Failure Patterns
Voltage stuck at 1.0V or below 0.8V regardless of throttle input
Cause: Contaminated or failed hot-wire sensing element, or broken signal wire
Diagnostic Tips
This engine has widespread issues with oil being drawn into the intake from the PCV system contaminating the MAF, especially after spirited driving. Clean with MAF-specific cleaner only, never carburetor cleaner. Verify no air leaks between MAF and throttle body which cause unmetered air and lean codes.
Related Diagnostic Trouble Codes
P0100P0101P0102P0103P0104
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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