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Can an EVAP be blue?

An EVAP (Evaporative Emissions Control) system is part of a vehicle’s emissions control system. Its purpose is to prevent fuel vapors from escaping into the atmosphere from the fuel tank and fuel system. The EVAP system captures these vapors and stores them in a canister filled with activated charcoal. When conditions are right, the vapors are pulled into the engine and burned during combustion.

The EVAP system is a closed system, meaning vapors should only flow in one direction – from the fuel tank to the charcoal canister to the engine. If vapor flow is impeded or blocked, pressure can build in the fuel tank. This is called a blocked or stuck closed EVAP vent valve. When this occurs, a number of different driveability issues can arise. One indicator of a blocked EVAP system is a fuel tank that will not accept its full volume of fuel at the gas pump before the pump shuts off.

So in regards to the original question – can an EVAP system be blue? Let’s take a closer look at the components that make up the system and see if a blue color is normal or a sign of a problem.

EVAP System Components

The major components that make up an EVAP system include:

  • Fuel tank
  • Fuel tank pressure sensor
  • Vapor canister – contains activated charcoal to absorb fuel vapors
  • Purge valve – mounted on canister, allows vapors to be pulled into engine
  • EVAP vent solenoid valve – mounted on canister, opens and closes to allow vapors to flow to canister
  • EVAP canister vent valve – relieves pressure build up in fuel tank
  • Various hoses and tubes

The most common colors used for EVAP system components from the factory are black, gray, or silver. Certain hoses may also be green, yellow, or orange. So generally, a blue colored component would not be an original factory part.

When an EVAP Component May Turn Blue

There are a few situations that could cause an EVAP component to turn blue:

1. Aftermarket Part

If a component has been replaced with an aftermarket part, the manufacturer may have used blue plastic or a blue coating. So this would not necessarily indicate a problem, just a non-OEM part.

2. Dye for Leak Detection

UV dye may be added to the EVAP system when performing a leak detection test. The dye will glow blue-green under UV light, allowing technicians to pinpoint the source of any vapor leaks. Some residue may be left behind after testing that causes a blue dye stain.

3. Oil Contamination

On rare occasions, an EVAP component may turn blue due to contamination from engine oil. This can occur if the PCV (positive crankcase ventilation) system is malfunctioning and allowing oil to be sucked into the intake manifold. The oil vapor can then make its way into the EVAP system through shared ports and hoses. When the oil condenses and leaves behind a film, it may have a blueish hue.

Blue EVAP Component – Cause for Concern?

A blue colored EVAP component does not necessarily mean there is a problem with the EVAP system itself. However, some additional investigation may be warranted to determine the cause:

  • Check component against factory part – is it aftermarket or OEM?
  • Inspect for dye residue if recent leak testing was performed.
  • Look for signs of oil contamination in the intake and EVAP system.
  • Monitor EVAP system operation for potential leaks or blockages.

Replacement of the affected component may be required if performance is compromised. But the root cause – whether an aftermarket part, dye residue, or oil contamination – should also be addressed.

Proper functioning of the EVAP system is important not just for emissions, but also for proper fuel tank venting and preventing vapor lock conditions that can affect drivability. So while a blue EVAP component may not be a definite problem, it’s wise to thoroughly inspect the system when an anomaly is noticed.

EVAP Systems and Emissions Testing

The EVAP system is monitored during OBD-II emissions testing. Multiple sensors watch for leaks and blockages. Any detected faults will cause the check engine light to illuminate and a diagnostic trouble code to be stored.

Common EVAP related trouble codes include:

  • P0440 – EVAP system leak detected
  • P0442 – Small EVAP leak detected
  • P0455 – Large EVAP leak detected
  • P0456 – Very small EVAP leak detected
  • P0446 – EVAP vent system performance
  • P0441 – EVAP incorrect purge flow

EVAP system faults must be corrected and the check engine light turned off before a vehicle can pass an OBD test. Repairs may involve:

  • Smoke testing to find leaks
  • Replacement of hoses, valves, or other components
  • Cleaning EVAP vent ports and canister
  • Reprogramming PCM to reset monitors

A professional grade OBD-II scan tool that can monitor EVAP system data is very helpful for diagnosing faults. Many code readers meant for DIY use lack live data capability.

Maintaining the EVAP System

The EVAP system is designed to be sealed and maintenance free. However, a few tips can help it remain trouble-free:

  • Do not overfill or top off the gas tank – allow room for expansion.
  • Tighten the gas cap until it clicks – cap must make a good seal.
  • Avoid spilling gas when filling – clean any drips.
  • Do not park vehicle in hot sun after refueling – allows vapors to dissipate.
  • Check for cracked, brittle, or missing hoses.
  • Replace vent solenoid valve if sticky or plugged.
  • Keep ORVR valve and vent ports clear of debris.

The EVAP canister should be replaced at least every 100,000 miles or per manufacturer recommendations. More frequent replacement may be needed if fuel odor is detected or evap faults set.


While a blue colored EVAP component is not normally expected, it does not necessarily indicate a problem. The most likely causes are:

  • Aftermarket replacement part with different color
  • Dye residue from leak detection
  • Engine oil contamination

Closely inspecting the EVAP system and addressing any detected leaks or blockages is recommended. And fixing evap codes promptly is key to passing emissions tests. With periodic maintenance and attention to potential issues, the EVAP system should provide reliable closed-loop control of fuel vapors.