Evaporative Emission System Leak Detected (Large Leak)

What it means

The evaporative emission (EVAP) system traps fuel vapour from the tank in a charcoal canister and later burns it in the engine. The ECU periodically seals the system and checks that it holds pressure or vacuum. This code means the ECU found a large (gross) leak in that sealed system.

Symptoms

• Check engine light on
• Faint fuel smell, especially near the filler or rear of the car
• No change in how the car drives

Probable causes

Most likely first

1. 1Fuel cap missing, loose or wrong type (most common)
2. 2EVAP hose disconnected or split
3. 3Purge valve stuck open
4. 4Vent valve stuck open
5. 5Cracked charcoal canister or filler neck

How to diagnose it

Work through these in order before buying parts

1. 1Record the code and its freeze frame data (speed, load, temperature when it set), then clear it and see if it comes back.
2. 2Check the fuel cap first: is it tight, is the seal cracked, and is it the correct cap? Tighten or replace it, clear the code and drive for a few days.
3. 3Inspect the filler neck for rust, and all visible EVAP hoses for cracks or disconnection.
4. 4Do a smoke test of the EVAP system; it is the quickest way to find small leaks.
5. 5Test the purge and vent valves for sealing with a hand vacuum pump.
6. 6Check for technical service bulletins (TSBs) or software updates for your make and model; some codes have known factory fixes.

Common fixes

• Tighten or replace the fuel cap
• Replace cracked EVAP hoses
• Replace the purge or vent valve
• Replace the charcoal canister
• Replace a rusted filler neck

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