P0300 — Random/multiple cylinder misfire detected
P0300 — Random/multiple cylinder misfire detected. Random multi-cylinder misfires are more serious than a single-cylinder miss: catalyst damage risk rises fast if the MIL flashes. Limit load and diagnose fuel, spark, and sync together.
Part of system: Electrical sensing & powertrain inputs
P0300 usually changes how the vehicle drives, shifts, or feels rather than creating an immediate emergency. P0300 reports random or multiple-cylinder misfires without pinning a single cylinder in the freeze frame. Crankshaft acceleration is uneven across several firing events, so the cause is often shared: lean fueling, low spark energy, contaminated fuel, mechanical imbalance, or ignition timing sync issues. Capture misfire counters per cylinder while the fault is active, then chase the common rail—coil power/ground, fuel pressure under load, and relative compression across all cylinders—rather than guessing one plug. Flashing MIL under load means catalytic risk; reduce throttle until the root cause is found. Sort among low fuel pressure or contaminated fuel affecting all injectors, shared ignition power, ground, or coil driver fault, and severe vacuum leak leaning multiple cylinders with a methodical road-test mindset. Begin with log per-cylinder misfire counts while reproducing the fault, continue with verify fuel pressure under wide-open-throttle snap tests, and consider full set of spark plugs matched to OEM heat range only after the data still condemns that part.
Vehicles often affected
Shows up after bad fuel batches, weak ignition power supplies, or cam/crank correlation issues on interference engines and high-mileage fleets.
Related video
How to fix a random engine misfire (P0300)
Typical symptoms
- Misfire counters climb on several cylinders at once
- Rough running that changes with humidity or fuel brand
- Power loss and bucking when climbing grades under load
- Catalyst temperature spike warnings after prolonged flashing MIL
- Fuel trims swing lean then rich as the ECM hunts mixture
Likely causes
- Low fuel pressure or contaminated fuel affecting all injectors
- Shared ignition power, ground, or coil driver fault
- Severe vacuum leak leaning multiple cylinders
- Cam/crank correlation error causing mistimed spark
- Evenly worn plugs or coils past service life
Recommended checks
- 1
Log per-cylinder misfire counts while reproducing the fault
- 2
Verify fuel pressure under wide-open-throttle snap tests
- 3
Load-test coil power and ground circuits at the harness
- 4
Compare relative compression across all cylinders
- 5
Address lean codes and cam/crank sync faults before parts roulette
DIY vs professional
DIY-safe: replace a full set of aged plugs and verify fuel brand/filter. Pro: relative compression, coil power/ground load tests, and timing correlation need a scope and OEM data.
Parts to replace
Full set of spark plugs matched to OEM heat range
Fuel filter or in-tank pump if pressure/volume fails
Ignition coils for cylinders that stay high after swaps
See also
Related discussions
Community threads about this fault code (external forums — opens in a new tab).