Charcoal Chamber

My 125,000 mile 10 year old Lexus RX 300’s check engine light came on. The dealer’s service department says the charcoal chamber needs replacing. How long can I drive around like this?

For as long as you would like to.

That depends.

Your gas tank breaths in and out through the charcoal bed in the canister. The activated charcoal catches the airborne hydrocarbon molecules to prevent them from escaping into the atmosphere.

If the charcoal bed is saturated such that the tank cannot breath in, a vacuum will develop in the gas tank’s airspace as gas is pumped out. The pump will then have to work against the vacuum to continue feeding the gas line. This can strain the pump and lead to premature pump failure. I’ve even read a case on an older system where the vacuum caused the tank top to collapse. A 20x20 inch surface has 400 square inches. A 2 PSI pressure on 400 square inches is 800 pounds of pressure.

Besides, if you leave the CEL lit and ignore it, how will you know if something engine-destructive happens that you might have been advsed of by the CEL?

I’d change it.

I would take it to a completely different mechanic - a local, independent shop and get a second opinion. You really don’t need to use a dealer unless you need warranty or recall service.

Many a charcoal canister has been replaced without need. This is one part of the evaporative emissions system and there is no computer diagnostic code that can tell you to replace it. What was/were the actual error code/s that came up? It may have been recorded on your invoice or auto parts chain stores often read them for free.

When you’re filling your tank at a gas station, do you keep going after the pump shuts off the first time? If so, this is much more likely to be a correct diagnosis.

It can also be a stuck check value in filler neck or a clogged or pinched vent hose any where from tank to the canister.

You should be aware that, if your state has emissions inspections, you will not be able to pass the emissions test until this problem is resolved.

Whether you need to have spider nests blown out of the evaporative emissions lines, or replace a solenoid valve in one of the lines, or unkink a line, or replace the carbon canister, repairs will be necessary in order to pass the emissions test.