Fumes in cabin of toyota prius

Our prius is 13 yrs old and the fan of the heat/ac broke. We had it replaced at the dealer and also had them replace the cabin airfilter.Since then, whenever we use the fan (heat or AC), we’ve been getting fumes in the car, a gas smell (even when there are no cars in front of us, so it’s not from other cars).We brought it back to the dealer twice and they have not fixed it.they found a hole in the exhaust system and replaced the muffler etc.
my question: 1) is there a way to measure the air quality in the cabin and find out what fumes are coming in and how dangerous they are?
2) What could it be and how can we finally get it fixed. Thank you for any input.

There’re sensors for measuring air quality, but nothing specific that I can find for automotive contaminants. You could use a CO2 home monitor operate on battery to see if your home limits are exceeded, but that doesn’t tell you about other contaminants. Your nose is a very sensitive monitor. If you continue to smell gasoline, you may have a leak in the gasoline supply system. The cabin air filter stops only particles, not VOCs, even if you replace the standard filter with a HEPA filter. HEPAs catch small particles than the standard filter, but not volatile chemicals like gasoline. Your exhaust repair should stop the exhaust odors. If thy don’t, the dealer didn’t repair all the leaking components.

Overall, I agree with jtsanders, but I want to clear up something that may be confusing for the OP. Specifically, I am referring to…
“You could use a CO2 home monitor”

I believe that jtsanders was recommending the use of a battery-powered carbon monoxide detector, but carbon monoxide is CO, not CO2.

CO2 is carbon dioxide, which is not lethal unless it is at very high concentrations.

Thanks for the correction. I should know better, but I hadn’t had my full morning transfusion of coffee. ; )

Do you smell gasoline or exhaust fumes? Folks will say gas meaning fumes and not fuel. If it is exhaust you have a risk of CO. Are you getting headaches? That is a symptom of CO. Both leaks are easy enough to find and fix. Ask around for recommendations for a different mechanic. Or click on the ‘Mechanics Files’ tab above to get the names of some mechanics close to you.

There may be a crack in one of the fittings or hoses of the evaporative emissions system that recaptures gas fumes from the gas tank and runs them through a charcoal canister, or rodents may have chewed through one of the lines.

Find a mechanic who can do a smoke test of the evaporative emissions system. The smoke will show where the gas vapor is leaking from.

I think you might have gotten the special VW upgrade.

Kidding aside, get the CO detector and check mostly due to the exhaust repair, but CO does not have any smells (unfortunately). Are you sure they have not botched the heater install. It might have some short or some burnt grease on it.