Audi P2404

Diagnose and fix Audi P2404

An Audi P2404 trouble code is a malfunction with the evaporative emissions systems. Specifically, a P2404 – EVAP System Leak Detection Pump Sense Circuit Range/Performance problem. The evaporative emissions system captures fuel vapor during fueling and stores the vapors in a charcoal canister. Later, when the engine is running, the system opens a purge and vent valve that allows the engine to suck vapor laden air into the engine where it is burned and also allows fresh air in to clean out the canister.

Evaporative emissions leak testing

Federal regulations require evaporative emissions testing to ensure system integrity. Different car makers use different testing techniques. On some vehicles, Audi uses a leak detection pump. Here’s how it works:

Audi leak detection pump

The leak detection system is designed to detect

Audi leak detection pump

leaks in the complete fuel system, including the fuel tank, EVAP canister and Evaporative Emission (EVAP) Canister Purge Regulator Valve/

The leak detection system has a vacuum-driven diaphragm pump with a reed contact on the actuation rod of the pump diaphragm. The engine supplies vacuum to the pump.

When activated, the diaphragm pump operates and pumps the fuel system up to 20 to 30-mbar. That pushes the diaphragm out so the reed contact at the operating rod is in the “open” position.

The system monitors the reed contact to ensure it opens within 15 seconds. That indicates the system is sealed. However, if the pressure falls (indicating a leak), the diaphragm moves back and the reed contact closes. If reed contact closes within 15 seconds a second test is actuated.

In the second test, the diaphragm pump operates 4 more times. The ECM measures the
time for each of the 4 pumps until the reed closes That’s how the ECM recognizes a “small leak” (smaller than 1 mm in diameter) or a “large leak”.

When the leak detection system operates

The leak detection system is activated shortly after each cold start (under 35°C) and when the vehicle is driven faster than 6.2-MPH (10 km/h). In the system detects a leak fault, it sets a trouble code.

What does Audi P2404 mean?

As mentioned above, the leak detection pump operates off of vacuum supplied by the engine while it’s running. The vacuum valve is an electrically operated solenoid valve. The ECM monitors the solenoid circuit integrity by looking for the voltage spike that’s present when the solenoid valve is switched OFF. The vacuum solenoid has a resistance of 15 Ohms.

When the vacuum valve is operating, it regulates vacuum flow based on a pulsed voltage from the ECM. The leak detection pump solenoid can fail due to an open or short condition.

Diagnose and fix an Audi P2404?

To conduct the full range of test, you’ll need a VAG scan tool. If you don’t have one, check the electrical connection to the vacuum valve and reed switch. Next, check for cracks in the rubber tubing to the leak detection pump. If the connections and tubing check out, replace the leak detection pump. It is the #1 cause of an Audi P2404.

©, 2018 Rick Muscoplat