P0300 on a 2018 Jeep Compass
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 Jeep Compass
Ranked from 929 NHTSA owner complaints filed for this vehicle.
- 1
Low compression from excessive oil consumption / worn piston rings
High severityThis generation's 2.4L Tigershark engine has a well-documented oil-consumption problem (subject of a factory recall); multiple owners here report the engine burning a quart every 1,000 miles, running rough with vibration, and stalling — consistent with rings/cylinders too worn to hold compression evenly.
Reported in 6 NHTSA complaints - 2
Worn or fouled spark plugs
Low severityOne owner's car stalled repeatedly at the same low-speed spot and ran fine after replacing spark plugs, a classic worn-plug misfire signature.
Reported in 1 NHTSA complaintParts:spark plug - 3
Failing ignition coil
Medium severityA weakening coil-on-plug drops spark energy on one cylinder under load; swapping coils between cylinders and re-scanning isolates the failing unit.
Common causeParts:ignition coil - 4
Clogged or leaking fuel injector
Medium severityA partially clogged or dribbling injector under- or over-fuels a single cylinder; injector balance testing isolates the culprit.
Common causeParts:fuel injector - 5
Vacuum/intake leak
Medium severityA cracked intake hose or leaking gasket admits unmetered air and can produce a lean misfire, especially at idle.
Common cause - 6
Carbon-fouled intake valves
Medium severityDirect-injected engines like the 2.4L Tigershark are prone to carbon buildup on the backs of the intake valves, disrupting airflow/fuel atomization enough to cause a rough-running misfire.
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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