P0350

P0350 means the ECM detected a primary or secondary circuit fault in an ignition coil but couldn't isolate which specific coil — it's the generic 'something's wrong on the coil driver side' code, usually thrown on older OBD-II systems (pre-2000) that lack per-cylinder coil monitoring, or on modern systems when the fault is shared across multiple coils (common ground, common 12V feed, or ignition module). Cheapest-first diagnostic: start at the coil power feed — key-on-engine-off, backprobe the B+ pin on any COP connector and confirm 12.0-12.6V with the engine off and 13.5-14.5V cranking; a reading under 10V cranking points to a corroded ignition relay, blown coil fuse, or voltage-drop in the harness ($5-$25 fix). Next, check the coil ground — voltage drop from coil ground pin to battery negative should be under 0.1V under load; anything over 0.3V means a corroded ground stud (clean and torque, $0 fix). Only after power and ground are clean do you scope the primary trigger signal from the ECM (looking for a clean 0-12V square wave at idle, ~6-10ms dwell) and measure secondary coil resistance (typical primary 0.4-2.0 ohms, secondary 6,000-15,000 ohms depending on platform). Don't condemn a coil pack on resistance alone — many coils fail only under load and read fine cold on a meter, so a power-balance test or scope capture is the real proof.

Vehicle-specific patterns: 1996-2000 GM 3.1L/3.4L V6 with the ICM-mounted-under-coil-pack design throws P0350 when the ignition control module fails — the symptom is intermittent no-start hot, and the fix is the $80-$140 ICM under the coil pack, not the coils themselves. 1996-1999 Ford 4.6L 2V with the rear-mounted DIS coil pack throws P0350 from cracked coil-pack housings letting moisture in; pull the pack, look for hairline cracks on the tower side. 1998-2003 Dodge/Jeep 4.7L early SOHC V8 throws P0350 from a failed ASD (auto shut-down) relay or chafed 12V feed running across the intake manifold — wiggle-test the harness with the engine running. 2000-2004 Toyota Tundra/Sequoia 4.7L 2UZ-FE with the original Denso COPs is famous for whole-bank P0350 events when the shared coil-side ground strap on the rear of the head corrodes — clean and retorque before buying eight coils. Estimated repair: $0 (clean ground) to $600 (full coil set + ICM).