Emissions repairs related to the fuel tank system can be complex, as the fuel system interacts with several other vehicle systems. 
A smoke test is a common diagnostic procedure used to pinpoint leaks in the system. 

Here’s a breakdown of what’s involved:   

Understanding the Fuel Tank System’s Role in Emissions:

The fuel tank system isn’t just about storing gasoline. It’s designed to minimize the release of harmful fuel vapors into the atmosphere.  These vapors are hydrocarbons, which are a type of volatile organic compound (VOC) that contributes to smog.  The system includes:   

• Fuel Tank: Stores the fuel and vapors.   

• EVAP (Evaporative Emission Control) System: Captures fuel vapors from the tank and stores them until the engine can burn them. This includes components like:

• Charcoal Canister: Captures fuel vapors.   

• Purge Valve: Draws vapors to the engine to be burned.   

• Canister Close Valve: Used for onboard testing.

The Smoke Test:

A smoke test is used to find leaks in the EVAP system.  Here’s the general process:

• Preparation: The technician disconnects a hose in the EVAP system and seals off other openings.

• Introducing Smoke: A smoke machine is connected to the system, and a safe, non-flammable smoke is introduced. In some instances, baby oil can be used.

• Visual Inspection: The technician visually inspects all the components of the EVAP system (hoses, connections, canister, etc.) for escaping smoke. Leaks will be indicated by smoke puffing out.

• Pressure Test:  A regulated pressure test is also performed along with the smoke test to help determine the severity of the leak.

• Diagnosis: Once the leak is found, the technician can identify the faulty part/s.

Common Fuel Tank System Emissions Problems and Repairs:

• Malfunctioning Purge Valve: The purge valve can get stuck open or closed, affecting the EVAP system’s operation. Repair: Replacing the purge valve.   

• Fuel Tank Leaks: The fuel tank itself can develop leaks due to damage or corrosion. Repair: In some cases, the tank can be repaired, but often it needs to be replaced.   

• EVAP System Sensors: Several sensors monitor the EVAP system’s performance. If a sensor fails, it can trigger a check engine light and affect emissions. Repair: Replacing the faulty sensor.   

• Leaking Fuel Cap: A loose or damaged fuel cap is a common cause of EVAP system leaks. Repair: Replacing the fuel cap.   

• Cracked or Damaged Hoses: Hoses in the EVAP system can crack or become brittle over time, leading to leaks. Repair: Replacing the damaged hoses.   

• Faulty Charcoal Canister: The charcoal canister can become saturated or damaged, preventing it from properly storing fuel vapors. Repair: Replacing the charcoal canister.   

What to Expect During an Emissions Repair:

• Diagnosis: The technician will perform a smoke test and other diagnostic procedures to pinpoint the source of the leak.

• Testing: After the repairs are made, the technician will perform another smoke test or other tests to ensure the leak is fixed.

• Check Engine Light: If the check engine light was on, it will be cleared after the repairs are completed. This is usually done in order to pass an emissions test. Your vehicles onboard EVAP readiness test will have to run and pass in order to successfully complete E-Check. This may take several drive cycles as conditions need to be satisfied.