Author Topic: P0456 evaporative emissions system small leak detected, DIY or mechanic? (Read 1619 times)

madmax

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The check engine light started showing up on my wife's 2004 Mercedes C240. I checked with an ODB tool and got the code mentioned in the description. After a quick Google search, I tightened the gas cap and cleared the code. Unfortunately, a few days later, the light is back on again.

After a quick search on MB forums, it seems that the problem is hard to diagnose but is typically solved by:
1) Replacing the gas cap
2) Replacing the purge control valve
3) Fuel tank sensor edited: sender

However, it is not guaranteed to be one of the above and is typically diagnosed with an expensive smoke machine.

I'm a bit overwhelmed by the lack of information available online and my unfamiliarity with how the evap system works. Should I throw some parts at the problem and hope it goes away? Or take the plunge and go to a good indy mechanic?

A third option is to try to make a "DIY Smoke Test Machine" as shown at https://youtube.com/watch?v=2U5kFib1WxE

I'm not a car expert but am just getting to the point where I'm comfortable handling routine maintenance on my cars such as Oil, Coolant, ATF and brake fluid changes. Apologize if this comes across as incoherent, I'm down with the flu and not thinking clearly.
« Last Edit: February 20, 2016, 01:04:48 AM by madmax »

Making Cookies

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Did you ever solve this? I have a similar problem on one of our cars.

Tackle it. You'll be smarter for it.

RurallyFrugal

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Similar code has happened to me on other cars. Usually it's a gas cap.

An alternative to a smoke machine is get yourself a decent cigar, pull a vacuum line, and with the engine off, blow in some smoke and see where any comes out. It may take a few puffs to get enough smoke in the system. If you have a leak it won't take long to find, plus you get an excuse to smoke a good cigar. Make sure to keep the cigar out of the engine bay, duh.

A PCV isn't that expensive; it may be worth a replace rather than a mechanic's labor rate.

If you're getting fuel to the motor, it's almost definitely not the fuel sender. When those things go bad, your car won't run usually.

My money would be on a gas cap given the age of your car.

JZinCO

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Oh Lord, I had a similar issue with an 86 Toyota pickup and replaced almost every part in Chilton's diagram of the emissions controls components. I couldn't imagine figuring it out on a newer car. Consider a middle ground approach: pay for a good diagnosis, buy the needed parts and then get your hands greasy. Getting parts for this system was hard because I had to call the dealership, cross-reference part ID's and then call part manufacturers direct rather than retailers.
Good luck
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madmax

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Wow, thanks for the replies specially RurallyFrugal. I've already tried a new gas cap, didn't work - code is back :( Will definitely try out the cigar method first - beats spending $100 on a smoke machine. I also got the Chilton manual for my car, thinking that it'll be useful for other things. Will update this thread, next weekend.

JZinCO

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Oh I forgot to add that if you have a charcoal canister sometimes you can replace just the filter. Not sure in your case. Also follow the rubber hoses in your evap line and look for dry rot
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big_owl

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Does the code ever go away? I've had this code for about 10 year now on my Subaru. Sometimes it goes away when the gas tank is full, only to come back on as the tank level gets lower.

In my case it is because of a gasket from where the tank filler pipe connects to the gas tank. I was rear-ended and my car's rear-end rebuilt but something was never right again. Not really DIY for me to drop the tank out and replace it, which I had done once only for the code to reappear a couple years later. They had to do the smoke test to figure out where it was coming from, and I had to take it to 2-3 different shops/dealers before one was finally able to pinpoint it. The only time I worry about it anymore is when I have to get a bi-annual emissions check.

Hopefully the source of your problem is a little easier to get to than mine is.