Evap Error Story

[RonB]

Hi, All

I was stuck in traffic one recent warm day for 45 minutes. Following that event, I had a "check engine" light. Using Torque Pro, I pulled the codes to see what happened.

I had 1 Evap failure, and 2 pending Evap failures.

I reset the codes, and have put 200 miles on it since.

What I think happened:
Our fuel injection systems are the "recirculating regulator" type. What that means is that the fuel pump, in the tank, runs wide open all the time. Any fuel that is not used by the engine is returned to the tank.

During the 45 minutes of idling, the quantity of fuel pushed into the engine compartment, warmed up, and then returned to the fuel tank generated so much vapor that it so overwhelmed the evaporative system that it threw the failure code.

Now that the code has been reset, it will probably be fine unless similar circumstances recur.

Moral of the story: Just like a loose fuel cap, a check engine light is not necessarily a hardware failure.

[Chiadog]

Is "Evap Failure" an actual code? Or did you get code numbers? Also, did you get any FF(freeze frame) data indicating all three codes were generated in that 45 minute period?

[jolt]

The evap system should be able to handle that. The only reason it was overwhelmed is that it is not operating correctly, which is why the error code came up. If you had just fueled the car full, or over full, and the fuel in the tank expanded because of heat, and the raw fuel flooded the charcoal carbon in the evap system, then the error code could be tripped but the medium that catches the vapors will clean itself with vacuum from the engine and the problem will go away over time. If you did not flood the evap system with fuel, you have a problem. As been talked about on this board before, bad hoses and vacuum leaks can cause the evap system to not be as effective as it was when new.

[circuitsmith]

Ninth gen Corolla/Matrix/Vibe has a returnless fuel system. No fuel return line to the tank.
The flow rate from the pump is low, which makes possible the "lifetime" fuel filter.

[lannvouivre]

Without the actual codes, your story is pretty much pure speculation.

[RonB]

I did not write down the actual code numbers, but I did make note of the type of codes.

I had driven at least 70 miles on the tank before being stuck in traffic, so it was not completely full, but was mostly full.

If any of the codes, or the check engine light, had recurred, further investigation would be required. However, with a couple thousand miles added, no check engine light has happened again. However, I also have not been stuck in traffic again either

<circuitsmith> You are correct, this vehicle has a returnless fuel system. So, my initial conjecture is incorrect. Unfortunately, that just makes it more difficult to correlate the facts to figure out why the check engine codes were set, but did not reccur.

[lannvouivre]

Just a glitch in the matrix. Pat yourself on the back, you fixed it! If you clear the code and it doesn't come back, there was never any problem.