Symptoms of a Bad Charcoal Canister | Autance

Knowing whether or not they have a bad charcoal canister in their vehicle is something many people would own up…

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Symptoms of a Bad Charcoal Canister | Autance © Symptoms of a Bad Charcoal Canister | Autance

Knowing whether or not they have a bad charcoal canister in their vehicle is something many people would own up to as being something they are not really aware of. After all, It’s just another of those technical things that take place beneath the bonnet, out of sight and out of mind for most people. Thankfully, the sophistication of todays engine management systems, (EMS), means that any minor problems that do occur are taken care of automatically or notified to the maintenance engineer during a routine service visit.

What Is A Charcoal Canister?

A car’s charcoal canister is a little known, but very important, part of the vehicle’s evaporative emission control system. This description is often abbreviated to “EVAP”. In many places it is a legal requirement that such a system is fitted to all new vehicles so, depending on the age and make of your vehicle, it may be necessary for you to do a little research in order to establish whether your vehicle has one.

The main purpose of the vehicle’s EVAP system is to capture the polluting fumes that are released, quite naturally, by the fuel in a vehicle’s fuel tank as it slowly evaporates and enters the atmosphere. This is not a new problem, and, in the past, it was usually solved simply by having a vent in the fuel tank cap though which the fumes could escape. Whilst that definitely did the trick and was successful in letting the fumes out of the tank, all that really happened using that system was that the toxic fumes were released from the tank, into the atmosphere, causing pollution and unpleasant odours in and around the vehicle.

A Bad Charcoal Canister Can Cost You Money In More Ways Than One!

Quite apart from the environmental problems caused by the toxic fumes that are released into the air by the fuel in a vehicle’s tank are the financial implications of such leakage for the car owner or driver.

Fuel that is lost through the evaporation process, cannot be burned by the car’s engine which means that the loss of evaporated fuel could be seriously reducing the vehicle’s overall miles per gallon performance.  With the pump price of motor fuel forever rising, that is very bad news indeed for the motorist, and even worse news for the environment in which we all have to live.

This problem affects petrol engines much more than it does diesel engines because the latter does not evaporate quite so quickly as petrol. If you live in a warm climate, or if it is the summer, then evaporation will take place even more quickly.

How Do You Know If Your Car Has A Bad Charcoal Canister?

Many vehicles are fitted with on board computers and have indicator lights or other indicator systems that will notify you when your car’s charcoal canister becomes faulty or worn and can no longer do the job properly. Many motorists never experience the problem of a bad charcoal canister because they are, up to a point, self-maintaining. They are fitted with a mechanism that periodically purges the charcoal filter in the canister and feeds the captured fumes back into the engine where they are burned in the combustion process. This ensures that the vehicle’s fuel economy is maintained, and the noxious fumes never get the chance to enter the atmosphere.

If the mechanism that enables this recycling of fumes ever becomes faulty, even if the charcoal filter itself is in good condition, the vehicle’s fuel economy will still be affected, and the vehicle could still be considered to have a bad charcoal canister that requires fixing or replacing.

What Are The Main Symptoms Of A Bad Charcoal Canister?

What should the motorist look out for when trying to establish whether their vehicle’s EVAP system is functioning properly?

  • Poor fuel efficiency – if the EVAP system isn’t working properly more and more of the fuel you buy and put into your car’s tank, is lost into the atmosphere where it is wasted. Although replacing a bad charcoal canister can be costly, so too can ignoring the problem. It won’t fix itself or get better over time and the cost of that wasted fuel just keeps on mounting up. This is undoubtedly the number one financial incentive for keeping the EVAP system in full working order.
  • Unusual noises coming from the engine bay – if the air to fuel ratio of the mixture being burned by the engine is not correct, then the engine can often make sounds that are unfamiliar to the motorist. This kind of noise doesn’t always indicate a fault with the charcoal canister however, there are other reasons why it might be happening, so it is important to get it checked out as soon as you can.
  • Low performance – if the air to fuel mix is not right then the car is highly likely to underperform and will often struggle with acceleration and other tasks such as ascending an incline. This can also be a problem if the car is heavily loaded, e.g. with several adult passengers or other heavy items.
  • Fuel smell in the cabin of the car and around the car – If the fumes cannot escape or if they are not absorbed by the carbon filter in the EVAP system, then they could find their way into the vehicle itself which is both unpleasant and dangerous. If you ever notice the smell of fuel inside the car, or around it, you should be sure to get it checked over by a qualified mechanic as soon as possible.

Although a faulty charcoal canister in your vehicle is unlikely to do serious damage it may be a legal requirement for you to get it fixed. Motorists should check the regulations in the area or country they live in so they can be sure they are complying with the applicable regulations.

We all want to save money – and the planet – so a well behaved and efficient charcoal canister is important for many reasons. Why not get yours checked out soon?


  1. Emission Control Systems – HowStuffWorks
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