P0300 on a Nissan Altima
P0300 means random/Multiple Cylinder Misfire Detected. On the Altima, a few causes come up far more than others.
What P0300 usually means on a Altima
P0300 on the Altima usually points to the ignition system first - the QR25DE is well known for ignition coils that fail with age and heat, and a wandering weak coil sets a random code. Catalyst substrate drawn back into the cylinders can also cause misfires on high-mileage cars, so it is worth ruling out on the QR25. Vacuum leaks and worn plugs round out the causes. It typically feels like a shake at idle or a stumble under load.
Most common causes on the Altima
- Failing ignition coils
The QR25 is hard on coils; a weak one wanders between cylinders and sets P0300.
- Worn spark plugs
Overdue plugs misfire across cylinders.
- Catalyst debris or low compression
On worn QR25s, ingested substrate can score cylinders and cause misfire.
- Vacuum or intake leak
A cracked hose or gasket leans several cylinders at once.
What P0300 costs to fix on a Altima
A full set of coils and plugs is a moderate cost on the four and all accessible on top of the engine. Diagnosis is cheap; a coil swap confirms a suspect quickly. If a compression test reveals cylinder scoring from cat debris, the repair becomes far more serious.
Year, engine and mileage change the answer. Start a case and Redline weighs these causes against what your car shows, then names the check that would settle it.
Other codes on the Nissan Altima
Related symptoms
Nissan Altima problems & recalls by year
Based on widely reported patterns for this model; individual causes vary by year, engine and history. Generic P0300 behavior is covered on the main P0300 page. Confirm with a scan tool before buying parts.
P0300 on your Altima?
Every problem becomes a Case. Tell Redline what your Altima is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.