P0300 on a 2015 Ram 1500
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 2015 Ram 1500
Ranked from 1,427 NHTSA owner complaints filed for this vehicle.
- 1
Crankshaft Tone Wheel Delamination
High severityThe magnetic material on the crankshaft tone wheel can delaminate, causing erratic or lost crankshaft position signals, leading to stalling and misfires. Confirm by inspecting the tone wheel through the sensor hole or dropping the oil pan.
Reported in 5 NHTSA complaints - 2
Exhaust Manifold Leak / Broken Bolts
Medium severityBroken exhaust manifold bolts are a known issue on the 5.7L Hemi, causing exhaust leaks that can skew O2 sensor readings and lead to misfires. Listen for a ticking noise on startup and look for broken bolt heads.
Reported in 3 NHTSA complaints - 3
Camshaft / Lifter Failure
High severityThe 5.7L Hemi is known for lifter failure that damages the camshaft, leading to misfires and a ticking noise. Confirm by inspecting the camshaft lobes and lifter rollers for wear or damage.
Reported in 2 NHTSA complaints - 4
Faulty Spark Plugs
Low severityWorn or fouled spark plugs are a leading cause of random misfires. Look for worn electrodes, carbon buildup, or incorrect gap.
Common cause - 5
Defective Ignition Coils
Medium severityFailing ignition coils can cause intermittent or consistent misfires across multiple cylinders. Confirm by swapping coils to see if the misfire moves or by testing coil resistance.
Common cause - 6
Vacuum Leaks
Medium severityUnmetered air entering the intake manifold leans out the air/fuel mixture, causing random misfires. Look for cracked hoses, a leaking intake manifold gasket, or a faulty PCV valve.
Common cause - 7
Low Fuel Pressure / Failing Fuel Pump
High severityInsufficient fuel pressure starves the engine, leading to lean misfires across multiple cylinders. Confirm with a fuel pressure gauge and check for a clogged fuel filter or failing pump.
Common cause - 8
Clogged or Faulty Fuel Injectors
Medium severityDirty or malfunctioning injectors may not deliver the correct spray pattern or fuel volume, causing misfires. Confirm via injector balance testing or checking for clogged screens.
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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