P0301 localizes misfire to cylinder 1 but does not identify the coil. Confirm cylinder 1 on the exact Pentastar, HEMI or other engine diagram, preserve counters, inspect the labeled plug and make one controlled ignition test. If the count stays, test injector delivery and compression/leak-down. On a 2015 WK 3.6L, bulletin 18-055-16 lists P0301 among PCM improvements, but exact engine/software applicability and normal mechanical testing still matter.
Match the symptom
Select the closest observation. The result changes the first test; it does not name a part to replace.
Stop loading.
What can set P0301—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 |
|---|---|---|
| Cylinder 1 plug fouled/worn/cracked | Abnormal deposit/gap | Labelled plug |
| Ignition component/circuit | Controlled test follows | Targeted ignition test |
| Injector fault | Count stays/contribution differs | Balance/command |
| Compression/valvetrain | Low mechanical contribution | Compression/leak-down |
| Cam/crank timing fault | P0016/P0340/sync data | Correlation diagnosis |
One coil swap should answer one question
Watch whether the misfire follows under the same cold or loaded condition; a scan counter is better evidence than whether idle merely sounds smoother.
If the event remains on cylinder 1, return the known-good coil and stop swapping. Fuel delivery and mechanical sealing have not yet been tested.
Plug deposits guide the next test
Oil, raw fuel, coolant-cleaned porcelain and excess gap point in different directions. Compare plug 1 with a neighboring cylinder before installing new parts.
Keep plug 1 labeled and photographed until diagnosis is complete. A mixed pile of plugs loses the cylinder evidence that makes P0301 useful.
Software cannot restore compression
The 2015 branch is conditional on WK, 3.6L ERB and calibration applicability. It should be checked, but not used to skip physical testing.
A PCM update cannot repair a leaking valve, worn rocker, damaged injector or cylinder sealing fault. Mechanical evidence still controls repairs.
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 cylinder 1
Use exact diagram.
- 02Preserve condition
Capture cold/load counters.
- 03Inspect plug
Keep labeled.
- 04Test ignition once
Watch whether count moves.
- 05Test injector and sealing
If it stays.
- 06Check timing companions
Do not ignore correlation.
- 07Retest
Verify original conditions.
Do not replace the most commonly named component from P0301 alone. Confirm the exact engine, preserve evidence and complete the manufacturer test sequence before ordering parts.
Why the model year changes the test
Grand Cherokee spans ZJ/WJ/WK/WK2/WL platforms and inline-six, V6, HEMI, diesel, turbo and 4xe powertrains. Oil-pressure control, EVAP hardware, cylinder banks, catalysts and cam sensors vary. Confirm platform, VIN, engine sales code, market and PCM calibration before using a bulletin or component diagram.
- 2015 WK 3.6L ERB has a specific PCM-update branch.
- HEMI cylinder 1 and MDS/valvetrain diagnosis differ from Pentastar.
- P0340/P0016 raises synchronization priority.
- Direct-injection fuel systems require pressure safety.
P0301 FAQ
Is P0301 always a coil?+
No.
Can I drive?+
Not with flashing MIL or shaking.
Can I swap coils?+
Yes when engine hardware supports it.
What if it stays?+
Test injector and compression.
Can valves cause it?+
Yes.
Why check timing codes?+
They may explain the misfire.
Should I clear first?+
No.
What confirms repair?+
No cylinder 1 counts 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.
01FCA Bulletin 18-055-16 — 2015 WK 3.6L PCM update2015 Grand Cherokee WK with 3.6L ERB; includes P0456 and P0301–P0304 among listed improvements↗02Stellantis/Mopar service informationFactory VIN-, platform-, engine-sales-code and calibration-specific service information↗03Mopar vehicle informationOfficial owner manuals and model-year engine, oil, warning and operating information↗