P0440 EVAP System Fault
Drive normally - check soon
The fuel vapor system failed a self-test, and the computer did not narrow it down further. Check the gas cap first, then the valves and hoses. The car drives the same.
- Safe to drive?
- Yes
- Typical cost at a shop
- $61-$643 RepairPal national averages, parts and labor
- Emissions test
- Yes, while the check engine light is on, most OBD emissions tests fail the car.
Read every EVAP code at once, clear them after the fix, and watch the EVAP monitor complete.
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What it means
Your fuel system is sealed so fuel vapor is stored in a charcoal canister and burned in the engine later. P0440 is the general code for a fault in that system. Some cars use it for a leak, others for a valve or sensor problem, so other EVAP codes and the carmaker's own description help narrow it down.
The technical version
The EVAP monitor tests both the seal of the system and the operation of its purge valve, vent valve and tank pressure sensor. P0440 is the broad code in the P0440-P0457 family. Many cars set a more specific code instead (P0442, P0455, P0446 and others), so a P0440 on its own often needs a shop smoke test and valve tests.
Official name: Evaporative Emission Control System Malfunction.
Symptoms
- Usually only the check engine light.
- Sometimes a fuel smell.
- Sometimes the tank is hard to fill.
Causes, most likely first
| Cause | How likely | How to tell |
|---|---|---|
| A loose or worn gas cap | most common | The cap does not click or the seal is worn. |
| A leaking hose or connection | common | A smoke test shows it. |
| A faulty purge or vent valve | common | Other EVAP codes, or the pump clicks off when you refuel. |
| A damaged charcoal canister | less common | Visible damage or charcoal dust in the lines. |
| A faulty tank pressure sensor | rare | Its reading does not change during the test. |
How likely is our ranking from repair data and common practice, not a published rate.
What the live data shows
There is no single live reading that proves this fault. The useful ones are fuel tank pressure (where fitted) and EVAP purge percentage. The real check is the EVAP readiness monitor: after a fix, it should show complete within a few days of normal driving, and the code should not return.
What to check first, in order
-
Check the gas cap: present, tight, clicks, seal not torn.
It is the cheapest fix.
What the data shows: No reading needed.
Cost: $138-$150 at a shop (Gas cap replacement, RepairPal)
-
Read all codes, including pending ones.
A second EVAP code tells you where to look.
What the data shows: Pending codes show early.
Cost: no cost if you have a scanner
-
Have a smoke test and valve test done.
It finds leaks and stuck valves.
What the data shows: Not a scanner step.
Cost: $61-$90 at a shop (Emission system diagnosis (shop), RepairPal)
-
Replace the faulty part.
A purge valve, vent valve, hose or canister.
What the data shows: EVAP readiness completes.
Cost: $210-$251 at a shop (EVAP purge valve replacement, RepairPal)
Is it safe to drive?
Drive normally - check soon
Yes. It is a fuel vapor fault, not a fuel leak.
Harmless to drive with. You may lose a little fuel vapor or smell fuel, and you will fail an emissions test until it is fixed.
Stop driving and get help if
- You see liquid fuel dripping or smell strong fuel inside the car.
What it costs
| Repair | Typical cost |
|---|---|
| Emission system diagnosis (shop)RepairPal, updated September 3, 2026 | $61-$90 |
| Gas cap replacementRepairPal, updated September 3, 2026 | $138-$150 |
| EVAP purge valve replacementRepairPal, updated September 3, 2026 | $210-$251 |
| EVAP canister replacementRepairPal, updated September 3, 2026 | $558-$643 |
National averages for the full job at a shop, parts and labor, from RepairPal (updated September 3, 2026). Your price depends on the car and the area. Many of the first checks on this page cost nothing with a scanner. The EVAP purge valve was CarMD's number 6 check engine repair in 2025, at an average of $172. CarMD averages come from a different method (repairs reported by its users), so they can sit below RepairPal's shop estimates.
Sources for the notes: CarMD 2026 Vehicle Health Index (press release, April 22, 2026).
Can I clear it? Will it come back?
The EVAP test only runs under certain conditions, often a cold start after the car has sat for hours, with the tank between about a quarter and three quarters full. After the repair, clear the code and drive normally for several days. The EVAP monitor should show complete and the code should stay away.
Will it fail an emissions test?
Yes, while the check engine light is on, most OBD emissions tests fail the car.
Related codes
How Obie handles P0440
Obie reads the EVAP codes and readiness, tells you what to check first, and tracks whether the EVAP monitor completes on later drives. Obie is part of ScanMyCar Pro. Codes and live sensors are free.
Questions people ask
Is P0440 the gas cap?
It can be. Check the cap first, then look for other EVAP codes.
Can I drive with P0440?
Yes. It does not affect how the car runs, but it fails emissions tests.
Why does my car have P0440 and not a more specific code?
Carmakers use the EVAP codes differently. A shop smoke test narrows it down.
Sources
- RepairPal: P0440 code page repairpal.com
- RepairPal: Emission system diagnosis (shop) (updated September 3, 2026) repairpal.com
- RepairPal: Gas cap replacement (updated September 3, 2026) repairpal.com
- RepairPal: EVAP purge valve replacement (updated September 3, 2026) repairpal.com
- RepairPal: EVAP canister replacement (updated September 3, 2026) repairpal.com
- CarMD 2026 Vehicle Health Index (press release, April 22, 2026) prnewswire.com
- Texas DPS emissions testing FAQ dps.texas.gov
- Arizona myazcar.com: OBD and the check engine light myazcar.com
A guide, not a diagnosis. This page describes what P0440 generally means across OBD2 cars. What is actually wrong with your car depends on its live data and its history, and any repair decision deserves a proper diagnosis, whether that is you with a scanner or a professional with a lift.