P0300 on a 2018 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 2018 Ford Explorer
Ranked from 713 NHTSA owner complaints filed for this vehicle.
- 1
Internal water pump failure allowing coolant intrusion into the cylinders
High severityExtensively documented design flaw on the 3.5L V6 (water pump mounted inside the engine, driven by the timing chain): multiple owners had coolant/oil found on spark plugs and cylinders, with dealers explicitly linking coolant intrusion to rough running, timing miss, and misfire.
Reported in 5 NHTSA complaints - 2
Fouled, stuck, or coolant/oil-contaminated spark plugs
High severitySeveral owners found a stuck spark plug or oil/coolant residue on the plugs when investigating a misfire, consistent with plugs fouled by internal fluid intrusion.
Reported in 4 NHTSA complaintsParts:spark plugs - 3
Ignition coil failure
Medium severityTwo owners had ignition coils replaced by the dealer as part of diagnosing a confirmed cylinder misfire (DTC P0303).
Reported in 2 NHTSA complaintsParts:ignition coil - 4
Timing chain slip or failure altering valve timing
High severityTwo owners had the timing chain slip on the highway, causing pistons to strike valves; incorrect valve timing produces severe misfire symptoms before catastrophic failure.
Reported in 2 NHTSA complaintsParts:timing chain - 5
Cylinder head defect allowing fluid to leak into a cylinder
High severityOne owner's mechanic confirmed cylinder head thinning causing a fluid leak into the first cylinder, described as a known long-standing EcoBoost issue Ford has not recalled.
Reported in 1 NHTSA complaintParts:cylinder head - 6
Vacuum or intake leak
Medium severityUnmetered air disrupts the air/fuel ratio enough to cause rough running that reads as a misfire.
Common cause - 7
Low cylinder compression (worn rings or valves)
High severityCompression loss, sometimes accelerated by coolant washing the cylinder walls, prevents a clean burn on the affected cylinder.
Common cause - 8
Carbon-fouled intake valves
Low severityDirect-injection carbon buildup disrupts airflow/atomization into the cylinder.
Common cause
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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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