P0300 on a 2017 Ram 2500
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 2017 Ram 2500
Ranked from 675 NHTSA owner complaints filed for this vehicle.
- 1
Intake air heater (grid heater) bolt/nut failure dropping into a cylinder
High severityExtremely well-documented 6.7L Cummins failure: the grid-heater retaining bolt/nut corrodes and drops through the intake manifold into a cylinder (commonly #6), destroying the piston and causing a severe misfire before total engine failure; often preceded by a P2609 intake-air-heater code.
Reported in 10 NHTSA complaints - 2
Worn or rounded camshaft lobe (valvetrain wear)
High severityOne owner's truck lost a cam lobe, causing a sudden loss of power and a confirmed misfire on cylinder 7; suspect if misfire correlates with a specific cylinder and no fuel/electrical fault is found.
Reported in 1 NHTSA complaintParts:camshaft - 3
Clogged or failing diesel fuel injector(s)
Medium severityA sticking or leaking injector unbalances combustion on that cylinder; check injector balance rates with a scan tool.
Common causeParts:fuel injector - 4
Low cylinder compression (worn rings or valves)
Medium severityReduced sealing prevents a clean, complete burn; confirm with a compression or leak-down test.
Common cause - 5
EGR valve/passage fault
Medium severityA stuck or heavily carboned EGR valve can upset combustion stability enough to misfire; inspect for carbon buildup and proper valve movement.
Common causeParts:EGR valve - 6
Charge-air/boost or intake leak
Medium severityA leaking intercooler boot or charge pipe upsets the air-fuel ratio under boost and can trigger a misfire under load; pressure-test the charge-air system.
Common cause - 7
Contaminated fuel or weak lift pump
Medium severityWater/contamination in diesel fuel or low lift-pump pressure starves injectors and produces misfire, especially under load; check fuel pressure and filter/water separator.
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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