Ignition Coil Primary
2021 Honda Civic · 1.5L I4 Turbo
Sensor Type
inductive
Waveform Type
pulse-width
Location
Individual coil-on-plug units mounted directly on each spark plug, cylinder head top
Pins
2-pin connector
Idle Frequency
25 Hz
Timebase
10ms/div
Voltage Scale
50V/div
Trigger
5V, falling edge
Wiring
Black/Yellow (ground) and Black/White (12V switched power from ECM)
Expected Voltage Range
At Idle
0V to 14V
At Higher RPM
0V to 14V
Expected Pattern
Sharp rise to 14V during dwell, rapid collapse to near 0V at firing, inductive spike to ~250V clamped by driver circuit
Known-Good Waveform
Clean square wave showing 2-4ms dwell time at idle increasing with RPM. Primary voltage rises sharply to battery voltage during dwell, then drops rapidly to trigger secondary. Inductive kickback spike should be clean and consistent around 250V, clamped by the ignition driver module. All four cylinders should show identical patterns.
Common Failure Patterns
Irregular dwell time, missing firing events, or reduced kickback voltage below 200V
Cause: Failing coil primary winding or internal coil driver circuit degradation
Diagnostic Tips
The L15B7 engine uses integrated coil drivers in the ECM, so compare all four coil patterns simultaneously. Honda coils on this platform are sensitive to oil contamination from leaking valve cover gasket causing misfire on cylinder 1.
Related Diagnostic Trouble Codes
P0351P0352P0353P0354
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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