2007 Check Engine light & fuel "venting"

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When the shop performed the OBD2 scan, did they supply you with the retrieved DTC (code)?

 

There are at least nine different diagnostic trouble codes which relate to the fuel tank.

"Venting" does not necessary imply that liquid fuel is being lost. Rather, fuel vapor may be lost due to inadequate performance of the fuel tank system. This lost vapor is not going to adversely impact mpg but is sufficient to register a DTC and cause you to fail emissions testing.

Yes, a sensor may have failed. You need to identify the specific DTC to have a further clue about what may be wrong with the system.

 

I wonder if your discount replacement fuel cap has failed?

 

Here is the workup for DTC P0456 (and P0442 / P0455) : https://share.qclt.com/%E4%B8%B0%E7%94%B0%E6%99%AE%E7%91%9E%E6%96%AF%E5%8E%9F%E5%8E%82%E8%8B%B1%E6%96%87%E6%89%8B%E5%86%8Cpdf%E6%A0%BC%E5%BC%8F/Repair%20Manual/04pruisr/05/2054m/cip0442.pdf

A quick call to a toyota parts counter, then ask how much a new cap costs.

 

California is not Louisiana the Air Quality Maintenance Division is even more tyrannical. Here that smog laws say there can be no MILs on (Mal Function Indicators) it doesn’t matter what they are for. In the case of my 2005 with 570,000 it was the coolant valve in the wrong position. Even changing the valve did not resolve the problem ( of course I knew if I was getting over 42 mpg driving at 75 there was not way I was hurting the air quality more than any car on the road getting less. Right?
I eventually found and replaced the faulty plug and resolved it only to find codes for the Evaporative fuel system, the O2 sensor 2 ( I had replaced with non OEM) and the Engine Control Module (ECM)
I had a 06 parts Prius so I swapped the ECM, Ordered an OEM O2 sensor and new exhaust gaskets for the mid section. I removed the gas Tanks and found when they were side by side they had different wiring harnesses ( see my other posts). After I put it back together the light wasn’t off! It said the tank pressure sensor was high, impossible right? Changed out the gas cap and it’s gone!
If you’ve replaced the gas cap and your code still says EVap system fault you need to drop the tank and replace the Evap canisters. Both of them while you are at it.
Hope this helps.


iPhone ?

 

Patrick Wong is correct. You need to find out what all the codes that are showing point to.
And sometimes, especially with hybrids the codes can be misleading, and point at everything except the real problem that is
causing all the other codes to trip. But once you find out what all the codes mean you have a much better chance of finding what the real cause of the problem is.
Evap codes can be as easy as the gas cap or can be things like the EGR valve or canister(s) or shut valve(s) O2 sensor(s) PVC valve etc.
Here is a diagram of the Evap system for a 2007 prius Touring Genuine OEM Emission Components Parts for 2007 Toyota Prius Touring - Olathe Toyota Parts Center

If you need to bring it to a mechanic and it turns out to be an Evap system issue, you may hear about a smoke test that is used to help a mechanic find a leak in the EGR system. That is if it actually is an Evap issue.

 

Are you doing the work yourself or are you taking it to a shop to have them do the work?

The small leak could be in the canister or shut valve or it could be in ten other places.
We can't be sure what it is with the data you've provided so far.

If all the shop sees is the one code, they don't know where the leak is either, most likely.