Ignition Coil Secondary
2021 Honda Civic · 1.5L I4 Turbo
Sensor Type
inductive
Waveform Type
pulse-width
Location
Secondary winding output at spark plug terminal within each coil-on-plug assembly
Pins
1-pin connector
Idle Frequency
25 Hz
Timebase
5ms/div
Voltage Scale
5kV/div
Trigger
2kV, rising edge
Wiring
Internal to coil assembly, connects directly to spark plug terminal
Expected Voltage Range
At Idle
-1000V to 35000V
At Higher RPM
-1000V to 40000V
Expected Pattern
Firing spike 15-25kV, spark duration 1-2ms, followed by coil oscillations at 10-50kHz decaying to baseline
Known-Good Waveform
Initial firing spike reaches 15-25kV for a healthy combustion chamber with proper compression and fuel mixture. Spark line should be relatively flat at 3-5kV for 1.5-2ms burn time, followed by clean dampening oscillations. Higher firing voltage indicates increased secondary resistance from worn plugs or lean conditions.
Common Failure Patterns
Firing voltage exceeds 30kV with short or absent spark line
Cause: Excessive spark plug gap (>1.2mm), carbon tracking in coil boot, or severe lean misfire
Diagnostic Tips
Use a 10:1 or 100:1 high-voltage probe designed for secondary ignition. OEM NGK spark plugs (SILZKR7B11) should be gapped at 1.0-1.1mm; this turbo engine is very sensitive to over-gapped plugs causing lean misfires under boost.
Related Diagnostic Trouble Codes
P0300P0301P0302P0303
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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