P2303

P2303 means the PCM detected a low-voltage condition on the primary control circuit of ignition coil B — the IGT command line to coil B is reading lower than the expected 0-5V (or 0-12V) reference, or the primary current is below the 5-15A peak the PCM expects during the 2-6 ms dwell. Cheapest-first ladder: (1) Inspect the coil B connector for green corrosion, bent or backed-out pins, and chafed wires — connector and harness faults make up the majority of low-side primary codes and cost nothing to find with a flashlight and a pick. (2) Ohm the primary winding pin-to-pin — spec is 0.4-1.5 ohms for most COP coils; 0.0 ohms indicates a shorted primary, OL indicates open, either condemns the coil. (3) Scope the IGT trigger pulse — clean 0-5V (or 0-12V) square wave with 2-6 ms dwell expected; missing pulse means the PCM driver or harness from PCM to coil is the problem. (4) Verify 12V feed pin at the coil with key-on — battery voltage expected; low or absent feed traces back to the ignition relay or fusible link. Expensive-misdiagnosis caveat: swap coil B with an adjacent coil and clear the code — if P2303 follows the coil to the new cylinder, it's the coil; if it stays on the original cylinder, it's the harness, connector, or PCM driver. A $40 coil swap-test saves the $80 misdiagnosis fee for replacing a coil that wasn't the problem.

Vehicle-specific patterns: 2005-2014 GM LSx V8 (LS1/LS2/LS3, Silverado/Camaro/Corvette) — primary-circuit codes on coils B (typically cylinder 3 or wherever the OEM map assigns B on a given platform) are common because the valve-cover-mounted coils take the brunt of exhaust-manifold heat soak. 2004-2010 Ford 4.6L/5.4L 3V Triton sees P2303 from the same melted/water-intruded connectors that plague all the per-cylinder coil codes on this engine — the COP connector sits in a low spot that collects condensation from the hood lip. 2011+ Ford 5.0 Coyote (Mustang GT, F-150) sees primary low-side codes from harness chafe where the COP pigtail loops over the intake manifold trim. 2007-2018 Toyota 2GR-FE 3.5L (Camry/Highlander/Sienna/RAV4) and 2AZ-FE 2.4L generally run 100-150K miles before throwing primary-circuit codes — when they do appear, the failure is usually a single coil rather than a set. Mercedes M271 (1.8L supercharged) and M273 (5.5L V8) coil primaries cluster at 80-120K miles, often with simultaneous failures across multiple cylinders. Common pattern: coil B typically = cylinder 2, 3, or whatever cylinder the OEM firing-order map assigns — verify against the OEM wiring diagram before swap-testing. Estimated repair: $40 (single coil DIY) to $320 (full set on a V8).