BMW fault code P0301 / 29CD (N54, N55): cylinder 1 misfire — the factory test path and the honest causes

P0301 is the same combustion-consistency measurement as P0300, but the counter that tripped belongs to one cylinder — cylinder 1 (BMW hex 29CD). That single fact collapses your search space: one hole is either not sparking, not injecting, or not compressing.

What the factory document says

The monitor runs between roughly 400 and 6,400 rpm, counting misses within 200 crankshaft rotations weighted by engine speed and load. The factory test sequence is the model of efficiency: visual inspection of spark plugs and ignition coils; if OK, switch positions — if the defect moves with the parts, replace them; then check ignition cables and wiring harness; then check the injector valve and the fuel system including the high-pressure pump. One more factory step most people skip: inspect the catalytic converter for damage — unusual colors on the casing, monolithic structure checked with an endoscope — because sustained misfire dumps raw fuel into the cat and cooks it.

What usually actually causes it

Community experience on N54/N55, paraphrased and ranked:

1. 01**Coil or plug on that hole.** The move-parts test exists because it's usually the answer. A single-cylinder misfire that appeared after a plug change is a cracked porcelain or a coil not fully seated.
2. 02**Injector** — index-mismatched or worn piezo injectors on N54 misfire on one cylinder, often when cold. The DME's injector calibration can't fix a mechanically tired injector.
3. 03**Valve cover gasket leak** letting oil pool around one coil boot — arc to ground, single-hole misfire, recurring after coil replacement until the cover is done.
4. 04**Low compression** on that hole — burned exhaust valve or ringland. The move-parts test fails to move the miss; that's your cue to do a compression or leak-down test before buying more ignition parts.

If multiple cylinders are counting, you're on the P0300 page↗ — different cause bias.

The fix path

• Run the factory move-parts test: [plugs and coils](../spark-plug-and-coil-guide) first, cheapest and most likely.
• Misfire that follows no part and persists cold → [log it](../reading-your-datalog): the per-cylinder misfire counters plus fuel trims point ignition vs fueling vs compression fast.
• Coil well oily → [valve cover and gasket](../valve-cover-and-gasket-guide), not another coil.
• Fixed the misfire but the CEL returns as [P0420](../fault-code-p0420)? The cat inspection step above is why — check it before assuming sensor drift.