OBD codes / P0300 / Jeep Grand Cherokee
P0300 on a Jeep Grand Cherokee
Random/Multiple Cylinder Misfire Detected
3.6L Pentastar V6 and 5.7L HEMI V8, WK2 (2011–2021) and later
What P0300 usually means on a Grand Cherokee
A P0300 on the Grand Cherokee means the PCM detected misfires spread across multiple cylinders rather than one specific hole. On the 3.6 Pentastar it most often traces to tired spark plugs and coils, but the engine's early cylinder-head history means a stubborn multi-cylinder misfire deserves a compression or leak-down check. On the 5.7 HEMI, random misfires frequently point at the valvetrain, a collapsing MDS lifter or a worn cam lobe, or simply overdue plugs. Vacuum leaks and weak fuel delivery round out the everyday causes.
Most likely causes on this model
- Worn spark plugs and coils
The HEMI runs 16 plugs and the Pentastar 6; an overdue tune-up is the leading cause of a random misfire on both.
- 3.6 Pentastar cylinder-head or valve issues
2011–2013 heads were prone to failure that can appear as a misfire, often starting on the left bank with a ticking noise.
- 5.7 HEMI lifter or cam wear
A collapsed roller lifter or flattened cam lobe on an MDS cylinder sets misfires along with a distinctive tick.
- Vacuum or intake leak
PCV and intake leaks lean out several cylinders at once and read as a random misfire.
- Low fuel pressure or dirty injectors
A weak pump or fouled injectors starves multiple cylinders under load.
What it costs on a Grand Cherokee
A full plug-and-coil refresh is the cheapest starting point and often the whole fix, running a few hundred dollars, more on the HEMI because of the doubled plug count. If diagnosis leads to a Pentastar head or a HEMI lifter and cam job, costs jump into the thousands. Getting an accurate misfire counter reading first keeps you from throwing parts at the wrong engine.
Fixing it
Start with correct-spec plugs and a coil inspection; if one cylinder keeps flagging afterward, move to compression testing before assuming an expensive head or camshaft repair.
For the full step-by-step diagnosis order (any vehicle), see the main P0300 guide.
Year, engine and mileage change the answer. Get a diagnosis for your Grand Cherokee — it weighs these causes against your exact configuration and real complaint data.
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Related symptoms
Jeep Grand Cherokee problems & recalls by year
Based on widely reported patterns for this model; individual causes vary by year, engine and history. Generic P0300 behavior is covered on the main P0300 page. Confirm with a scan tool before buying parts.