P0300 on a 2010 Cadillac Srx

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 2010 Cadillac Srx

Ranked from 474 NHTSA owner complaints filed for this vehicle.

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1
Stretched/worn timing chain causing cam-crank correlation misfire
High severity
By far the dominant pattern in this batch: rough idle, random stalling, and check-engine events repeatedly traced to a stretched timing chain (often flagged as code P0017), a well-known high-mileage failure on this engine that throws the cam/crank timing off enough to misfire.
Reported in 10 NHTSA complaints
Parts:timing chain timing chain guides crankshaft position sensor
2
Internal engine damage (rod/rod-bearing failure)
High severity
Two owners had a broken connecting rod or bad rod bearings diagnosed, which produces a knock and can present as a severe, unrecoverable misfire on the affected cylinder.
Reported in 2 NHTSA complaints
Parts:connecting rod bearings
3
Worn spark plugs
Low severity
Aged or fouled plugs are the single most common general cause of a random misfire code and the first thing to rule out.
Common cause
Parts:spark plug
4
Failing ignition coil(s)
Medium severity
A weak or dying coil-on-plug unit misfires under load; usually confirmed by swapping coils between cylinders.
Common cause
Parts:ignition coil
5
Clogged or leaking fuel injector(s)
Medium severity
An injector delivering too little (or dribbling) fuel starves or floods a cylinder enough to misfire.
Common cause
Parts:fuel injector
6
Vacuum leak
Medium severity
Unmetered air entering the intake leans out one or more cylinders enough to misfire, especially at idle.
Common cause
7
Carbon-fouled valves
Low severity
Carbon buildup on the intake valves disrupts airflow and fuel atomization, a common contributor to random misfire on higher-mileage engines.
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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Matching symptoms

Car Runs Rough Flashing Check Engine Light