Ignition Coil Secondary
2021 Honda Accord · 1.5L I4 Turbo
Sensor Type
inductive
Waveform Type
pulse-width
Location
Secondary winding internal to coil-on-plug assembly, measure using capacitive pickup clamp around coil tower or spark plug wire adapter
Pins
Unknown
Idle Frequency
25 Hz
Timebase
2ms/div
Voltage Scale
5kV/div
Trigger
2kV, rising edge
Wiring
N/A - internal coil connection to spark plug terminal
Expected Voltage Range
At Idle
-2000V to 35000V
At Higher RPM
-2000V to 40000V
Expected Pattern
Firing spike to 8-15kV, burn time plateau at 2-4kV for 1-1.5ms, followed by coil oscillations and spark line
Known-Good Waveform
Initial firing line peaks at 8-15kV under normal conditions, immediate drop to relatively flat burn voltage of 2-4kV lasting 1-1.5ms. After spark extinction, 4-6 clean oscillations decreasing in amplitude. Burn time consistent across all cylinders within 0.3ms variance.
Common Failure Patterns
Firing voltage exceeds 20kV with short or absent burn time, irregular spark line
Cause: Excessive spark plug gap wear (>1.3mm), lean mixture increasing resistance, or fouled plugs
Extremely short burn time under 0.8ms or intermittent spark line dropout
Cause: Coil saturation issues, weak coil output, or carbon tracking in coil boot
Diagnostic Tips
Honda specifies NGK DILKAR8A8S or DENSO DXUH24C (iridium) plugs at 0.8-0.9mm gap. Turbo engines show higher firing voltages under boost conditions. Compare cylinder-to-cylinder consistency as 1.5T engines commonly develop intake valve carbon buildup affecting compression balance after 40k miles.
Related Diagnostic Trouble Codes
P0300P0301P0302P0303
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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