P2304

P2304 is a generic OBD-II code meaning the PCM detected high voltage on the Ignition Coil B Primary Control Circuit — the ECM's coil driver (typically a high-side or low-side switching transistor inside the PCM or in an external ignition module) saw a voltage on the coil control pin that was stuck high when it should have been pulled to ground during the dwell/spark event. On COP (coil-on-plug) systems, each coil is on its own primary circuit, so 'Coil B' is cylinder-specific per the manufacturer's coil-numbering scheme (NOT always cylinder 2; check the FSM coil map). Cheapest-first ladder: (1) Swap the suspect coil with an adjacent cylinder's coil, clear the code, and drive — if the code follows the coil to the new cylinder, the coil's primary winding is open (no current path means the driver sees the rail voltage on the control pin) and the coil is bad. If P2304 stays on the original cylinder, the problem is downstream (harness or PCM driver). (2) Ohm the coil primary winding from the control pin to the B+ feed pin — healthy coils read 0.5-1.5 ohms primary on most modern COP designs; open circuit means burned winding ($30-180 part). (3) Backprobe the coil control wire with a scope and watch the primary waveform — you should see clean 0V-to-12V switching with a sharp inductive kick (200-400V flyback) on coil-off; a flatline at 12V means open primary circuit, a flatline at 0V means short to ground in the control wire. (4) Check the coil feed fuse and the ASD/main relay output — if multiple coils throw similar codes simultaneously, the fault is upstream of the coils, not in any individual coil. Expensive-misdiagnosis caveat: don't replace the PCM for a P2304 driver fault before verifying the coil itself isn't drawing excessive current and overheating the internal driver — a coil with shorted primary turns pulls 20+ amps and physically destroys the PCM coil driver MOSFET; replacing the PCM without replacing the coil that killed it leads to a destroyed second PCM in days.

Vehicle-specific patterns: any modern COP-equipped platform can throw P2304 — Ford EcoBoost 2.0/2.3/3.5L commonly sees P2304 from coil boot carbon-tracking that bleeds primary current to chassis ground, killing the boot first and the driver second. GM LSx and LT-series V8 (5.3L/6.0L/6.2L) throws P2304 from heat-soaked coils mounted on the valve covers — the OEM round-can coils degrade in clusters around 100k miles and replacing all 8 as a set is standard. VW/Audi 2.0T TSI/TFSI (EA888, EA113) sees P2304 from the well-documented coil-pack failures that VW eventually addressed by switching to redesigned R8-style coils on warranty. BMW N20/N52/N54/N55 throws P2304 from coil and boot failures together. Honda K-series and J-series, Toyota 2GR/3UR, Hyundai/Kia Theta/Lambda — all COP designs are susceptible. The pattern is universal: heat + age + ignition stress = coil primary failure, and swap-test is the 5-minute diagnostic. Estimated repair: $40 to $1,200.