BMW 29D1 identifies cylinder 5 misfire, not the failed component. Preserve cold/load smooth-running data, inspect labeled plug 5 and perform one controlled coil comparison. On a qualifying N54, BMW's cold-start injector bulletin requires reproducible roughness plus wet-plug/injector evidence; it is not an N55 shortcut. If the fault stays, test rail pressure, injector contribution, rear intake sealing, compression/leak-down and cam timing.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Stop loading to protect catalysts.
What can set 29D1—and how to separate it
The order below is evidence-driven, not a universal probability ranking. Vehicle year, repair history, companion codes and the operating condition in freeze frame change where diagnosis should begin.
| Possible cause | Evidence that supports it | First useful test |
|---|---|---|
| Worn/fouled plug or ignition fault | Cylinder leader and controlled swap follows | Labelled plug/ignition test |
| Injector or fuel-pressure fault | Contribution/pressure mismatch | Injector/fuel tests |
| Intake, purge or boost leak | Trim/smoke pattern | Smoke and purge test |
| Compression, valvetrain or timing fault | Count stays with mechanical weakness | Compression/leak-down/timing |
| Shared voltage or contaminated fuel | All cylinders or post-refueling | Voltage/fuel-quality test |
Record cold-start behavior
Capture cylinder 5 correction from the first cold revolution and keep every removed component labeled.
A fault that follows the coil and one that remains on cylinder 5 require different next tests.
Use the correct injector branch
Apply the N54 bulletin only when production, engine and physical evidence match. Program injector compensation as BMW directs after valid replacement.
On N55, use its current ISTA pressure and injector test rather than N54 index rules.
Check rear-runner air and mechanics
Smoke-test local manifold/CCV plumbing, then perform compression and leak-down if fuel/ignition do not move the fault.
Verify the original condition without 29D1.
Save these scan-data clues
Freeze frame is a snapshot of conditions when the PCM matured the fault. It can distinguish an idle-only problem from a load, cold-start or monitor-completion problem. Clearing first throws that context away.
- Exact VIN, platform, model year and engine sales code
- All confirmed, pending and permanent companion codes
- RPM, load, coolant temperature and vehicle speed
- Relevant commanded and actual scan data
- Recent service, repairs and symptom conditions
- Manufacturer bulletin and current software/VIN status
A practical diagnostic workflow
- 01Identify engine and bank layout
Cylinder patterns differ.
- 02Preserve counters
Save cold/load evidence.
- 03Inspect plugs in order
Deposits direct testing.
- 04Target ignition
Use one controlled test.
- 05Test fuel and air
Graph pressure/trims and smoke paths.
- 06Prove mechanical health
Use compression/leak-down/timing.
- 07Verify original condition
Avoid a flashing-MIL road test.
Do not replace the most commonly named component from 29D1 alone. Confirm the exact engine, preserve evidence and complete the manufacturer test sequence before ordering parts.
Why the model year changes the test
BMW 335i diagnostics divide primarily between twin-turbo N54 E9x cars, single-turbo N55 late-E9x/F30 cars and market-specific variants. The engines share a badge but not boost actuators, injectors, Valvetronic hardware or fault-code families. Confirm VIN, chassis, production date, engine, DME software and modifications before applying an N54 30FF or N55 2C57 procedure.
- Cylinder 5 sits toward the rear of the inline-six; confirm the exact diagram.
- N54 and N55 injector hardware/coding differs.
- Wet fuel, oil ash and unusual cleaning point to different causes.
- 2A82/2A87 companions raise VANOS/oil-supply priority.
29D1 FAQ
Does P0300 mean all coils failed?+
No.
Can I drive?+
Not with flashing MIL or strong shaking.
Can bad fuel cause it?+
Yes.
Should I replace plugs first?+
Inspect and record them first.
Can vacuum leaks cause it?+
Yes.
Can timing cause it?+
Yes, especially with cam/crank codes.
Why save counters?+
They reveal cylinder and bank structure.
What confirms repair?+
Stable counters under original conditions.
Ford diagnostic references
These documents explain Ford monitor operation. Exact pinpoint tests, connector views and specifications must be selected for the truck's VIN and model year in current service information.
01BMW SIB 13 04 09 — N54 cold-start misfireProduction-bounded N54 branch for reproducible cold-start rough running, wet plugs and proven high-pressure injector faults↗02BMW Technical Information SystemOfficial VIN-, engine- and ISTA test-plan information↗03BMW owner's manualsOfficial VIN/model operating, warning and maintenance information↗