Emissions control: EGR, DPF, catalytic converter and AdBlueGeneric OBD-II codeUrgency: Monitor
Code P0442: EVAP system: small leak detected
P0442 means: evaporative emission control system (EVAP): small leak detected.[1][2][3][4] The control unit has detected a small leak in the EVAP system, the closed circuit that collects petrol vapours from the tank into the canister and sends them to the intake to be burned. To check that it is sealed, the control unit closes the vent valve, activates the purge valve and monitors whether the expected pressure or vacuum is reached. If it is not reached, it interprets this as a leak.[1][2][3]
What code P0442 means
The control unit has detected a small leak in the EVAP system, the closed circuit that collects petrol vapours from the tank into the canister and sends them to the intake to be burned. To check that it is sealed, the control unit closes the vent valve, activates the purge valve and monitors whether the expected pressure or vacuum is reached. If it is not reached, it interprets this as a leak.[1][2][3]
AutoDTCs places the threshold for a small leak at an opening equivalent to a hole of about 0.5 mm (0.020 inches), compared with just over 1 mm for a large leak (P0455). These figures come from a single source: each manufacturer sets its own. The same source describes a typical monitor that needs a warm engine, the tank between 15 and 85% and about 15 to 20 minutes of mixed driving with stretches at constant speed.[1]
The EVAP self-test only runs under certain driving conditions, so after a repair the light may take a few days to go off.[2]
Original definition (SAE J2012): Evaporative Emission Control System Leak Detected (Small Leak)[1][2][3][4]
Causes of P0442
From most to least likely, according to the sources.
- 1Fuel cap with a degraded seal or not closed properly. It is the most common cause the sources cite, and the first thing to check.[1][2][3]
- 2Rust on the sealing surface of the cap, on the filler neck, or a corroded neck seam (especially where salt is used in winter).[1][2]
- 3EVAP hose or pipe with a fine crack, or a quick connector loosened by vibration.[1][2][3]
- 4Vent valve (canister close valve) that does not close properly or leaks, or a purge solenoid valve with a leaking diaphragm.[1][2][3][4]
- 5Cracked activated carbon filter (canister).[1][2][3]
- 6Damaged or rusted fuel tank, faulty tank pressure sensor, or a failed leak detection pump.[2][3]
Symptoms
- Engine fault warning light on, often the only symptom.[1][2][3][4]Engine warning light: faults that cause it
- A slight smell of petrol near the car or when parked in a garage, easier to notice in the heat.[1][2][3]Fuel smell: faults that cause it
- A “loose cap” warning on the instrument panel, on cars that have one.[2]
- Difficulty refuelling if a valve or hose is blocked.[2]
How to diagnose P0442
In order: from the most likely and cheapest to check to the most expensive.
- 1Check the cap: the seal must not be cracked or deformed and must close fully. Clear the code and complete a driving cycle; if it does not return, the leak was the cap.[1][2][3][4]
- 2Read the other EVAP codes. Mechanic Base indicates that P0440, P0441 or P0446 together with P0442 may point to a more complex leak, a defective canister or a faulty solenoid valve.[3]
- 3Carry out a smoke test with a smoke machine, blocking the canister vent outlet. A small leak can take between 30 and 90 seconds to release smoke, and UV-dye smoke helps to see it. Samarins warns that without a smoke machine and advanced diagnostic equipment, diagnosis is difficult.[1][2]
- 4Trace the EVAP hoses from the tank to the engine, looking at the quick connectors, at points near heat sources where the plastic becomes brittle, and at chafing points.[1][3]
- 5Test the vent valve (normally open, closes when powered) and the purge valve (normally closed, can be tested with a vacuum pump) separately. With a bidirectional tool, command them to close and watch the tank pressure: a valve that does not seal counts as a leak even if the hoses are fine.[1][2]
- 6Check the canister, the filler neck and the tank for cracks or rust.[1][2][3]
- 7If you cannot find the cause, look for the manufacturer's technical bulletins for your model. On VW and Audi, Ross-Tech recommends checking the cap and the purge valve N80.[2][3][4]
Can I keep driving with P0442?
Monitor
AutoDTCs rates it as low severity, with no effect on performance or safety, and advises repairing it before an emissions inspection. It warns that a small leak can get worse, especially if it is a crack in a part exposed to UV light. Mechanic Base agrees it can usually wait a little, but says it is best repaired as soon as possible because vapours continue to escape, and notes that a damaged tank is more urgent because of the risk of fuel leak and fire. With the code active, the light does not go off.[1][3]
Documented faults related to P0442
Known faults of specific engines and cars, with their repair cost, the affected years and their sources.
Engine sensors: the most serious faults by engine and car
- High severityFrequency: Occasional2.0 DTI and 2.2 DTIVP44 injection pump and air mass meter failureGerman Wikipedia documents recurring failures of the Bosch VP44 injection pump and the air mass meter in the early years of this engine. An owner testimony for this engine describes the pump being replaced at 192,500 km, at a cost the owner calls «prohibitive».
- Medium severityFrequency: Common2.0 TDIClogged particulate filter or faulty pressure sensorThe 2.0 TDI's particulate filter clogs if the car mostly makes short journeys, because it never gets to regenerate; sometimes the fault is just the differential pressure sensor. Cleaning it costs around €200 and replacing it, €800 to €3,000.Repair (garage): €800–€3,000
- Medium severityFrequency: Common1.4 and 1.6 8vCrankshaft position sensor failure (TDC sensor)The crankshaft position sensor (capteur PMH, or TDC sensor) appears repeatedly in the reliability sources for the Clio II, the Kangoo I and the Dacia Logan I with this engine, with hard cold starting or stalling as the main symptoms. It is a cheap part, but the failure can leave you stranded.
- Medium severityFrequency: Common1.4 and 1.6 16vCrankshaft position sensor failureThe crankshaft position sensor (capteur PMH) appears repeatedly in the reliability sources for almost every generation with this engine, with hard cold starting, stalling or the car cutting out unexpectedly. It is a cheap part, but the failure can leave you stranded.
Frequently asked questions
Can I drive with code P0442?
Yes. The sources consider it an emissions fault with no risk to the engine or to driving. It is worth repairing before an emissions inspection, and checking the tank as soon as possible if there is a smell of fuel or dripping.[1][3]
Is it always the fuel cap?
It is the most common cause and the first thing to rule out, but not the only one. AutoDTCs names the cap seal as the first suspect; Samarins adds rust on the filler neck, the vent valve and the purge valve as the other usual culprits.[1][2]
What is the difference from P0455 and P0456?
It is a matter of the size of the leak the control unit detects. P0442 is a small leak, P0455 a large one and P0456 a very small one. AutoDTCs gives about 0.5 mm as a guide for small and more than 1 mm for large, but the thresholds vary by manufacturer.[1][2]
I have repaired the leak and the light is still on; what happens?
Samarins explains that if the fault has been fixed but the code has not been cleared, the light can take a few days of driving to go off, because the EVAP self-test only runs under certain conditions. Confirm with the diagnostic equipment that the EVAP monitor has completed.[1][2]
Will I pass the MOT with code P0442?
If the code has switched on the engine warning light, no: with that light on, the inspection records a serious defect, and on Euro 5 and Euro 6 cars the ITV (Spain's roadworthiness inspection, similar to the MOT) also reads the OBD diagnostic system. Repair the fault before you go; clearing the code just before the inspection does not help either, because it counts as a serious defect.[5]
Not sure what is wrong with your car? Describe what you notice in the symptom diagnosis or see all fault codes.
Sources
Every fact on this page links to its source. If you find an error, let us know.
- P0442: Evaporative Emission System Leak Detected (Small Leak)AutoDTCs · Technical documentation · consulted 31 October 2026
- P0442 EVAP System Leak Detected (Small Leak)Samarins.com · Technical documentation · consulted 31 October 2026
- P0442 – Evaporative Emission Control System Leak Detected (Small Leak)Mechanic Base · Technical documentation · consulted 31 October 2026
- 16826/P0442/001090 - EVAP Emission Control Sys: Small LeakRoss-Tech Wiki · Technical documentation · consulted 31 October 2026
- Desmontando mitos: ¿puede pasar mi coche la ITV con el testigo de «avería motor» encendido?Diariomotor · Motoring press · published 8 March 2021 · consulted 2 October 2026 · in Spanish