P0300 on a 2020 Honda Odyssey
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 2020 Honda Odyssey
Ranked from 430 NHTSA owner complaints filed for this vehicle.
- 1
Worn or spun connecting rod bearings (bottom-end wear)
High severityMultiple owners report engine knocking/ticking sounds and confirmed connecting rod bearing failure on this 3.5L V6, referenced by owners to NHTSA Action PE25008; bearing wear drops cylinder compression and produces persistent misfire before catastrophic failure.
Reported in 6 NHTSA complaintsParts:connecting rod bearings - 2
Weak or failing high-pressure fuel pump (low fuel pressure)
Medium severityOne owner reports a loud high-pressure fuel pump with a vibrating fuel line and a check-engine code for low fuel pressure, which starves cylinders of fuel and produces a misfire under load.
Reported in 1 NHTSA complaintParts:high-pressure fuel pump - 3
Worn spark plugs
Low severityAged or fouled plugs widen the spark gap and misfire under load.
Common causeParts:spark plugs - 4
Failing ignition coils
Medium severityA weak coil produces an intermittent single-cylinder misfire; swap-test between cylinders to confirm.
Common causeParts:ignition coil - 5
Clogged or leaking fuel injectors
Medium severityUneven injector delivery causes a lean or rich misfire on the affected cylinder.
Common causeParts:fuel injector - 6
Vacuum leaks (intake or PCV hoses)
Medium severityUnmetered air causes a lean misfire most noticeable at idle.
Common cause - 7
EGR valve fault
Low severityA stuck-open or clogged EGR valve dilutes the air/fuel charge and causes misfire at idle/low RPM.
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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