Gas Cap Check Engine Light

Welcome to PC! I wonder if it would work to disconnect your 12V battery ground wire for a minute. That will clear most any code. If the problem is still there, the code will come back before long. But, it will also clear all you radio presets and any other changes you've made from the default settings.

 

2015? I'd let the dealer handle it. Is it still under warranty?

 

How many ignition On-Off cycles have occurred since tightening? Some of these temporary CEL indications are tied to power cycles, not miles or time.

 

One thing you need to know is, there can be lots of reasons for the check engine light to come on. They all have different codes so you can tell them apart. A loose gas cap is one possible cause, so if the light came on and you decided the cap wasn't totally tight, sure, you may assume the two things were related, but until you read out the code, that is only an assumption. The ECU may have detected some other issue at around the same time, and at this point, you've put on 300 more miles without looking into what it is.

So, never mind about using a code reader to clear the code. Start by using a code reader to read the code!

If you get one of the codes for an evaporative-emissions leak, and you're sure it was the loose cap, then sure, clear the code, see if it comes back. If it does, you might have another leak to track down.

If it comes back any other of the possible engine trouble codes, then you just need to fix whatever problem it indicates (or have it fixed).

-Chap

 

For anyone searching for this -

The EVAP code takes a lot of drive cycles to reset and only in very specific conditions, such as the tank being more than 1/4 but less than 3/4 full for the test to even run.

Options
1 - drive normally for two or three tanks. Check Engine Light should go away on its own.
2 - disconnect the 12v battery under the passenger rear seat for 10 minutes. This also resets all your instrument settings, radio, and sets all your car's emissions monitors to "not ready" for a while, but the check engine light will be off.
3 - get an OBD-II scan tool and read and erase the code yourself. This also sets the emissions monitors to not ready but leaves your car's settings intact.

If you are in a state where has to pass emissions - Don't do option 2 or 3 before your test is due. Those monitors need to all be ready to be able to take the emissions test.

 

If you do battery disconnect and then drive for say a couple of weeks, that should be ok too: it get's back to normal, would pass inspections ok?

 

I think it'll probably be okay. I was an emission inspector in Pennsylvania, and while I did emissions monitor diagnostics on a LOT of different cars - but I never even saw a Prius with a check engine light or any emissions problem.

Most emissions tests allow ONE monitor to be "not ready" as long as the check engine light is off. It's almost always invariably the EVAP test. This is one reason that most states that do emissions tests also pressure test the gas cap.

Many of the monitors will turn to "ready" on the very first drive within 5 minutes. The oxygen sensor monitors, the catalytic converter monitor and EVAP monitor are the long ones.

Fuel vapors are actually the biggest contributor to smog - more than what the car is burning. That's why the emissions systems are so focused on the gas cap problem. That's also why they always say to fill up at night or evening when it's cooler than in the middle of a hot day. Although California's gas pumps (and a few other states) have special gas pump nozzles that help reduce the amount of fuel vapors.

 

I have a 2014 prius and codes P0441 P0455 and P0171 came on...added an oil can catch a few months ago and thought this could be the issue..symptoms are idling goes up and down...google says it might be a gas cap or purge valve issue..replaced gas cap first, cleared codes and symptoms went away..all good now..now i have spare purge valve in stock