Strong smell of gas from rear of vehicle and CEL

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Mazda 5
I have a 2006 Mazda5 with approx 58k miles on it. The car had a strong smell of gas coming from the rear of the vehicle after a short drive on Saturday night, still smelled like gas both outside the rear of the vehicle and inside the rear of the vehicle late Sunday morning and there was a CEL. The car had also randomly downshifting to 3rd from 4th after shuddering during the past two weeks and would not shift back up to 4th without slowing down to 2nd.

The car had also been having trouble after rain, it would go into limp mode often with a CEL and transmission light on during the past year or so. It would be fine after turning it off or drying out but it continued, so I had the throttle body replaced at the end of August thinking that would solve the problem.

I took it to the dealership yesterday and they showed codes for faulty turbine and temperature sensors, so now limp mode makes sense, however, they cannot find anything that would have caused the gas smell, which is now gone. Mechanic doesn't think that those two faulty sensors would have anything to do with the gas smell. Any ideas or suggestions? Thanks!
 
As far as the gas smell, do you sometimes top off your tank by continuing to pump gas in after it initially stops? This could saturate your charcoal filter and over time render it useless and display a CEL and cause other smog related sensors to fail.
 
As far as the gas smell, do you sometimes top off your tank by continuing to pump gas in after it initially stops? This could saturate your charcoal filter and over time render it useless and display a CEL and cause other smog related sensors to fail.

We don't top off when we refuel, so I am confused by what could have caused it. The car was probably last filled at least a week ago, if not longer. It was very strong on Saturday night (first time we'd noticed it) and Sunday but I did not smell gas at all yesterday when I drove it to the dealer.
 
Stupid question, but this is the type of stuff you should rule out first before going for the more in-depth troubleshooting: Is it possible it was user error? Spill fuel at your last fill up? leave gas cap loose?

Did you notice particularly bad fuel mileage on that tank?
 
Stupid question, but this is the type of stuff you should rule out first before going for the more in-depth troubleshooting: Is it possible it was user error? Spill fuel at your last fill up? leave gas cap loose?

Did you notice particularly bad fuel mileage on that tank?

No, the gas cap was fine. There were no visible leaks, and the car had not been fueled for at least a week. There was no noticeable difference in gas mileage and no drop in the level of the fuel in the tank. It only happened once, and in conjunction with CEL. After waiting a day, there was no CEL when I started the car and no smell of gas.

Mechanic says that the fuel system is holding pressure but scanned and found two codes , fault in turbine sensor and fault in temperature sensor. Mechanic does not seem to think that those faults could have anything to do with the gas smell, but I can't think of any other possible explanation for it. It seems strange that there would only be a smell of gas in conjunction with a CEL...seems like it would have to be related to the sensors?
 
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