Emission codes
P0442: evaporative emission system small leak
P0442 is a leak code with a size attached: the fuel vapor system holds pressure, but loses it a little too fast, as through a hole about the size of a pin.
P0442: can I drive, and what will the labor cost?
Estimated labor, replace the gas cap
$11 to $22
| Labor time (estimate) | 0.1 to 0.2 h |
| Rate used | $110/h |
| Technician wage, United States (average) | $27.13/h |
| Low: fix when convenient Safe to drive; fix it before your next emissions inspection. | |
Labor only: parts and the diagnostic fee are not included. Hours are our estimate for a typical car; book times vary by model. Wage: BLS, May 2025.
P0442 is the generic OBD-II code for "evaporative emission system leak detected, small leak". During its self-test the computer seals the vapor system, applies a vacuum or pressure, and measures how quickly it decays. A small leak lets the pressure change at a rate that matches a hole of about 0.040 inch, the size the federal rules required systems to find before stricter limits took over (40 CFR 86.1806-05). Leaks that small are invisible and silent. The most frequent causes are a gas cap whose seal has hardened or that was not clicked shut, and a fine crack in one of the rubber vapor hoses, often near the canister or the top of the tank where heat and age harden them. A purge valve that does not seal completely and a seal at the filler neck or the tank's fuel pump access come next. It is safe to drive; fix it before your next emissions inspection.
After the repair: when does the light go off?
Light off by itself after about
2 days
| Fault-free trips needed | 3 |
| Warm-up cycles before the code can be erased | 40 |
| Stored code gone after about | 40 days |
Federal rule for model years up to 2016 (40 CFR 86.1806-05); a misfire or fuel fault must also stay away under similar conditions. Clearing codes with a scanner also resets the readiness monitors an inspection checks.
Codes, rules and labor data checked by Radif Partners · Editorial policy · Method and sources
P0442 at a glance
| Code | P0442 |
| Standard description | Evaporative Emission System Leak Detected (Small Leak) |
| System | Evaporative emissions (EVAP) |
| Severity | Low: fix when convenient |
| Common symptoms | none, slight fuel smell |
Why a new cap is a sensible first step
A cap costs far less than any diagnosis and is the single most frequent cause of small and large leak codes. Fit one made for your vehicle, tighten it until it clicks, and drive normally. If the code returns within a couple of weeks, the cap was not the problem and the next step is a smoke test. Keep the old cap in the glovebox for comparison.
How a smoke test works
The shop connects a machine to the EVAP service port or the filler neck, closes the vent valve with a scan tool, and pushes a harmless vapor into the system at low pressure. Smoke appears where the leak is, sometimes with the help of a UV dye and a lamp. It usually takes half an hour and an hour and finds hose cracks, loose clamps and leaking seals that no visual check could. The hose under the car is often the culprit on older vehicles in salt states.
Size matters for the diagnosis
A very small leak, about 0.020 inch, sets P0456; a gross leak or no seal at all sets P0455. Knowing which one you have tells the shop how carefully to look. Cars of model year 2017 and later test to the stricter 0.020-inch limit described in 40 CFR 86.1806-17.
Likely causes of P0442, in order
| Cause | How often |
|---|---|
| Gas cap seal worn or cap not clicked | most frequent |
| Small crack in a vapor hose | most frequent |
| Purge valve leaking | frequent |
| Leaking filler neck or tank seal | less frequent |
P0442 repairs and labor time
| Repair | Labor (estimate) | At $110/h |
|---|---|---|
| Replace the gas cap | 0.1 to 0.2 h | $11 to $22 |
| EVAP smoke test to find the leak | 0.5 to 1 h | $55 to $110 |
| Replace a vapor hose | 0.3 to 1.5 h | $33 to $165 |