OBD-II Code
P2305
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$15–$400
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
$15 (boot + dielectric grease) to $400 (full coil set on a V8).
P2305 means the PCM detected a fault on the SECONDARY circuit of ignition coil B — the high-voltage side that fires the spark plug, typically diagnosed by the PCM watching burn-time (spark-line duration, healthy is 0.8-2.0 ms) or detecting that the demanded 15-40 kV firing voltage exceeded the coil's capacity.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP2305 means the PCM detected a fault on the SECONDARY circuit of ignition coil B — the high-voltage side that fires the spark plug, typically diagnos…
P2305 means the PCM detected a fault on the SECONDARY circuit of ignition coil B — the high-voltage side that fires the spark plug, typically diagnosed by the PCM watching burn-time (spark-line duration, healthy is 0.8-2.0 ms) or detecting that the demanded 15-40 kV firing voltage exceeded the coil's capacity. Open-secondary is the most common P2305 subcondition: failed secondary winding, carbon-tracked boot, or burned-through spring contact between the coil tower and the plug terminal.
Cheapest-first ladder
- Pull coil B and inspect the boot for carbon tracks (wandering black lines on the inside insulation), oil contamination from a leaking valve-cover gasket, or arc-through holes — a $15 boot + dielectric grease resolves a large share of P2305 cases.
- Pull the plug and read it — normal-but-dead = no spark reached it; sooty/fouled = secondary fired but plug was contaminated.
- Ohm the secondary winding through the plug tower — spec is 5K-25K ohms depending on platform; OL confirms an open secondary.
- Scope the secondary with a kV probe — firing line above 25 kV with a short or missing burn line indicates open secondary, worn plug, or wide gap stressing the coil. Expensive-misdiagnosis caveat: swap coil B to an adjacent cylinder before replacing — if P2305 follows the coil, it's the coil; if it stays, the spark plug, plug well, or harness is the cause. A $40 coil swap-test saves $80.
Vehicle-specific patterns2004-2010 Ford 4.6L/5.4L 3V Triton dominates P2305 case files for the same reason it dominates all per-cylinder secondary codes — the long extension…
- 2004-2010Ford 4.6L/5.4L 3V Triton dominates P2305 case files for the same reason it dominates all per-cylinder secondary codes — the long extension boot down into the deep plug well traps moisture, oil mist, and carbon, then carbon-tracks the boot insulation and shorts secondary voltage to the cylinder head before it reaches the plug. Replacing the boot and spring contact at every spark-plug service prevents the majority of these codes.
- 2005-2014GM LSx V8 (LS1/LS2/LS3) sees boot rubber hardening and cracking from valve-cover-mounted heat exposure around 80-100K miles.
- 2011+Ford 5.0 Coyote uses a shorter boot than the Triton but still tracks around 90K miles.
- 2007-2018Toyota 2GR-FE / 2AZ-FE secondary failures tend to be full-coil failures rather than boot-only — Toyota's coil tower is more sealed than the Ford design. Mazda RX-8 Renesis rotary uses paired trailing and leading coils with a much higher firing frequency than a piston engine — leading coils fail first around 50-70K miles, secondary symptoms identical to P2305. Mercedes M271/M273 coil-pack secondary failures cluster at 80-120K miles. Common pattern: coil B usually maps to cylinder 2 or 3 depending on OEM firing-order assignment — verify against the OEM wiring diagram.
Estimated repair$15 (boot + dielectric grease) to $400 (full coil set on a V8).
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