P0300 on a 2016 Ford Mustang
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 2016 Ford Mustang
Ranked from 367 NHTSA owner complaints filed for this vehicle.
- 1
Coolant intrusion into cylinders from head-gasket/engine-block failure (2.3L/5.0L)
High severityThis Mustang generation is heavily documented for head-gasket and block failures that let coolant into the cylinders; owners pulled misfire codes (P0301/P0303) with rough idle and white smoke before full engine failure.
Reported in 17 NHTSA complaintsParts:head gasket - 2
Ignition coil failure (cylinder-specific)
High severityTwo owners had a faulty ignition coil confirmed on the same misfiring cylinder (#3), diagnosed alongside spark plug and coil-pack replacement.
Reported in 2 NHTSA complaints - 3
Vacuum leak (intake/vacuum sensor circuit)
Medium severityOne repair order for a cylinder-3 misfire also called for replacing a vacuum sensor alongside the plugs and coil, pointing to a vacuum-side contributor.
Reported in 1 NHTSA complaintParts:vacuum hose - 4
Worn spark plugs
Medium severityStandard high-mileage wear item and the most common overall P0300 cause; check gap/fouling first.
Common causeParts:spark plugs - 5
Clogged or leaking fuel injector
Medium severityA partially clogged or dribbling injector unbalances one cylinder's fuel delivery, producing a repeatable misfire.
Common causeParts:fuel injector - 6
Carbon-fouled intake valves (direct-injection engine)
Medium severityDirect-injection engines like the 2.3L EcoBoost build carbon on the backs of the intake valves over time, disrupting airflow/atomization and causing misfire.
Common cause - 7
Low compression from worn rings/valves
Medium severityReduced cylinder sealing lowers combustion efficiency enough to register as a misfire, especially at idle.
Common cause - 8
Faulty EGR valve
Low severityA stuck-open EGR valve dilutes the intake charge unevenly and can cause a rough idle/misfire condition.
Common causeParts:EGR valve
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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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