P0300 on a 2017 Ford Explorer
P0300 is a generic OBD2 powertrain code for random or multiple cylinder misfire. Unlike P0301 through P0308, it does not point to one specific cylinder, so the cause can be ignition, fuel, air, sensor, or mechanical.
Not your vehicle? See general P0300 info.
Most common causes on the 2017 Ford Explorer
Ranked from 1,669 NHTSA owner complaints filed for this vehicle.
- 1
Coolant intrusion into cylinders (often due to internal water pump failure)
High severityCoolant leaks internally, mixing with oil or entering cylinders, causing misfires, rough idle, and white smoke. Look for coolant loss with no external leaks, milky oil, or misfire codes.
Reported in 11 NHTSA complaints - 2
Oil leaking onto spark plugs/into cylinders
High severityOil leaks foul the spark plugs, leading to misfires and rough running. Look for oil pooling in spark plug wells or burnt oil smell.
Reported in 2 NHTSA complaints - 3
Variable Valve Timing (VVT) / Cam Phaser failure
Medium severityFractured or failing VVT components/cam phasers can disrupt engine timing, leading to misfires and rough running. Listen for abnormal engine ticking or rattling.
Reported in 2 NHTSA complaints - 4
Failed ignition coils or spark plugs
Low severityWorn or failed ignition coils and spark plugs are standard causes for misfires. Look for worn electrodes or failed coil packs.
Reported in 1 NHTSA complaint - 5
Vacuum leak
Medium severityUnmetered air entering the intake manifold causes a lean condition, leading to random misfires. Look for cracked hoses or intake manifold gasket leaks.
Common cause - 6
Fuel delivery issues (e.g., failing fuel pump or clogged injectors)
Medium severityInadequate fuel pressure or poor injector spray patterns can cause lean misfires across multiple cylinders. Check fuel pressure and injector operation.
Common cause
These causes are aggregated from NHTSA owner complaints and general repair knowledge — this is not a diagnosis. P0300 on your car still needs shop confirmation before any repair.
Common symptoms
- Flashing or steady check engine light
- Rough idle
- Shaking under acceleration
- Loss of power
- Fuel smell from exhaust
What to check before replacing parts
Scan for cylinder-specific misfire codes
Look for: A companion P0301–P0308 pins the misfire to one cylinder — start there. P0300 with no cylinder code points at something hitting several at once: fuel pressure, a large vacuum leak, or timing.
Inspect the spark plugs and coils
Look for: Pull the plugs: black/sooty = rich, oily = oil intrusion, white/blistered = lean or overheating, cracked porcelain or an out-of-spec gap = replace. Then swap a coil to another cylinder — if a cylinder-specific code follows the coil, the coil is bad.
Check fuel trims for a vacuum leak
Look for: High positive short- and long-term trims (worst at idle, improving as RPM rises) mean unmetered air is getting in. Smoke-test the intake and listen for hissing.
Verify fuel pressure
Look for: Compare running/cranking pressure to the vehicle spec. Low or dropping pressure starves multiple cylinders and reads as a random misfire — suspect the pump, filter, or regulator.
Compression / leak-down test if ignition and fuel check out
Look for: A cylinder 15%+ below the others, or leak-down hissing from the intake (intake valve), exhaust (exhaust valve), or oil filler (rings), means the misfire is mechanical — not a swap-in part.
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