Ignition Coil Primary
2021 Honda Accord · 1.5L I4 Turbo
Sensor Type
inductive
Waveform Type
pulse-width
Location
Individual coil-on-plug units mounted directly on each spark plug, accessed from top of engine under plastic cover
Pins
2-pin connector
Idle Frequency
25 Hz
Timebase
5ms/div
Voltage Scale
100V/div
Trigger
50V, rising edge
Wiring
Black/Yellow (12V battery feed from main relay), Blue/Black (ECM switching ground control)
Expected Voltage Range
At Idle
0V to 350V
At Higher RPM
0V to 400V
Expected Pattern
Rapid rise to ~350V at coil cutoff, oscillating decay with 3-5 diminishing peaks over 1-2ms dwell period
Known-Good Waveform
Sharp voltage spike to 300-400V when ECM cuts primary current, followed by 3-5 clean oscillations decreasing in amplitude. Dwell time increases with RPM, typically 2-4ms at idle. Clean baseline at battery voltage between firing events with no noise or hash.
Common Failure Patterns
Reduced spike voltage below 250V or irregular oscillation pattern with fewer than 3 peaks
Cause: Coil internal breakdown, shorted windings, or weak primary circuit
Diagnostic Tips
Honda 1.5T coils are prone to carbon tracking on the boot area. Check for even firing across all four cylinders. Verify 12V supply is stable during cranking as voltage drops below 10V can cause weak spark and misfire codes.
Related Diagnostic Trouble Codes
P0351P0352P0353P0354
Always confirm waveform data with your vehicle's OEM service manual before diagnosing.
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