P0456 on a Nissan Altima
P0456 means evaporative Emission System Leak Detected (Very Small Leak). On the Altima, a few causes come up far more than others.
What P0456 usually means on a Altima
P0456 is the small-leak counterpart on the Altima, caught by the tighter monitor. Because the leak is pinhole-sized, a smoke test is essentially required to find it. The gas cap seal and Nissan's vent and purge valves are the usual sources, along with hairline hose cracks. Diagnosis typically outweighs the parts cost.
Most common causes on the Altima
- Weeping gas cap seal
A worn cap O-ring passes large-leak testing but fails the small-leak monitor.
- Vent or purge valve not sealing
Nissan valves that will not fully seat leak the small volume this code detects.
- Tiny hose or grommet cracks
Age-hardened lines leak just enough to trip P0456.
What P0456 costs to fix on a Altima
Invest in the smoke test to pinpoint the pinhole on the Altima. The parts - cap, a valve, a length of hose - are inexpensive. Expect diagnostic labor to be the larger share of a small-leak repair.
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 P0456 behavior is covered on the main P0456 page. Confirm with a scan tool before buying parts.
P0456 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.