eduncanz28

Hello, I am new to the forum, the frustrated owner of a 2012 GL 550 I purchased certified pre-owned. Soon after I bought it, the Check Engine light (CEL) comes on. Dealer says charcoal canister replaced. One month goes by. CEL back on. Back to dealer-he says he drained fuel tank and replaced fuel tank pressure sensor. Another month goes by, and CEL comes on again. By this time, I own an OBD II scanner I bought for an older Suburban I own. OBD II flashes P0451 - Evaporative Emission System Pressure Sensor/Switch Range/Performance. Anybody have ideas? Seems like dealer struggling with same problem. Yes, I am under warranty, but dealer is 120 miles away and usually sits on vehicle several days waiting on parts when he has it. Thanks for any thoughts anybody may have!

YodaSyrup

Check your state's lemon law - sounds like you are on your way.

eduncanz28

Think lemon laws only apply to new car purchase, not certified-preowned.

fabbrisd1

So you know proper fueling procedure is to stop when the pump stops - this particular code can come about with owners "topping off".

The proper diagnostic procedure at the dealer is a leak test of the fuel system in the back end.

Keep the beat !

eduncanz28

Thanks for the tip about not topping off. I don't, but will reinforce to the wife. Appreciate it!

YodaSyrup

You are correct, lemon laws do not apply to CPO or used - I missed that in your original post. Unfortunately, your best bet is to find a competent dealer who can diagnose and repair issues on the first attempt. I know it sounds counterintuitive, but after three tries, you might want to try a different dealer. Instinct is to stay with them until they get to the bottom of it, but my experience has been the opposite.

Some dealers (especially those with high volume service departments) don't assign the same tech to your car on repeat visits, the new tech doesn't take the time to look at the history of previous repairs and ultimately, nobody owns the issue. Despite your frustration, they are organized to be efficient, not to 'get to know' your car and it's issues. Smaller service departments are usually better at this.

I too had a CEL problem with a CPO S class (3 separate visits), it wasn't until I tried another smaller dealer that it was resolved.

BTW and FWIW, I called Mercedes HQ on that car and they told me straight up - based on my service history, they would have bought the car back if I had purchased it new and had those issues. But with a CPO, they would only keep trying to fix it under warranty, they do not buy back CPOs.

desant89

This is not true at least in NJ where I am. I have used the Lemon law on a pre-owned vehicle before, and was taken care of.

eduncanz28

This particular vehicle was purchased in NC and registered in GA. Both of these states' Lemon Law only apply to new cars. Thanks for everybody's input. I am erasing the code with my OBD II scanner and hoping it does not come back, but I have a feeling it will. YodaSyrup, I actually do have a smaller dealer closer to me. At this point, I am willing to consider anything. Thanks for everyone's help!

jasonjeross

Proper diagnostic test is a smoke kit that will find the leak.

Unfortunately MB only scans for codes and follows procedures based on the code.

No code? No work.

Code? Same procedure.

Perhaps the most incompetent manufacturer support network I have ever seen.

sak335

I've chased a similar problem on a BMW before and I can tell you that it is frustrating at best. In my case (my old 1996 M3) it was a valve in the expansion tank that was stuck. I blew compressed air into it and it freed up and no more problems after that.

Prior to finding the problem, I probably spend 20 hours going round and round and testing everything twice over. Smoke test will find a leak, but it isn't always a leak. I'm not familiar with the MB system, but there are several small valves that open and close during the test cycle at startup that are also suspect.

In general here's how the system works:

1. When you start the vehicle, the car initiates a self check by closing all the vent valves in the fuel system (if the system weren't vented the fuel tank would expand in the heat and contract in the cold due to the volatility of fuel)
2. The system checks pressure via a sensor
3. After a certain period of time, the system checks pressure again.
4. If the pressure has dropped, the system assumes a leak and sets the MIL

In my case, the valve in the expansion tank was stuck open so the system could never check system pressure and set the MIL every time.

Again, this was a BMW but it was a Bosch system so likely very similar to what MB uses.

jasonjeross

Nice to hear from a real mechanically inclined person. I'd fall over dead if any of the "techs" at a dealer would know half of the details of the expansion valve system in their cars.

Reality is this will likely not be fixed. By "fixed" I mean the dealer will simply swap parts that hopefully encompass the system (when in reality they should be properly diagnosing instead of code reading and replace the ONE part that is actually bad/less money to repair).

sak335

That appears to be the consensus regarding Mercedes service, which is a shame on many levels. I've not had to bring my GL in for any repairs yet so I don't have any experience.

I started working on cars when I was a kid, and I still enjoy it, though it is getting frustrating with the level of electronics these days and the need for a factory computer (or equivalent) to read, reset, or modify code. I'm a bit perplexed why so many forum members seem to continue to use dealer service when there are so many good independent shops out there that don't just throw parts at a problem. My guess is that many folks have extended warranties through Mercedes and that drives them to the dealers.

I'll touch wood, but I haven't had a car (out of warranty) at a shop in well over ten years, and i don't intend to bring one in any time soon.

eduncanz28

Yeah, I definitely hear you on dealer service. Unfortunately, or fortunately depending on how you look at it, I am in warranty, so I am left with going through the dealer as my only option. Although this is my first Mercedes, I have an unimaginable number of very unsatisfactory encounters with Mr. Goodwrench over the years, to the point it has peaked my interst in doing my own car work as much as I can.

BIGsmoke

Regarding doing you own repair work.
"It is not your ability, it is your desire."
Funny, how the dealer creates the desire to not go back.

eduncanz28

You got that right-for sure!

kcpj.1970

I just got done fixing the P0455 "everything seems to be working" EVAP problem. There are a lot of "guesses" on the net to what the actual issue is that lights the CEL around the net. You're looking to diagnose a "gross" leak, meaning:

a) the cap is off,
b) the EVAP purge solenoid is not sealing (under the hood),
c) the lines are broke or disconnected
d) the canister is cracked, or,
e) the EVAP canister vent valve (behind the rear passenger wheel, in the canister) is not working properly.

It is really simple to diagnose on a GL. You don't have to smoke the system either:

0) get a vacuum kit at Harbor Freight.

1) connect the vacuum to the vent hose and pull a vacuum

2) if vacuum DOESN'T hold, then:

3) go to your EVAP purge solenoid under the hood and pull vacuum from the fuel tank side. if you can't get vacuum...then that is most likely the problem.

4) If the EVAP purge solenoid holds vacuum, then it is either the line or canister (which are both the least likely to be the problem), OR,

5) the gas cap (which the code, message center and blinking fuel light say it is). This is a cheap $10-$15 part at your LAPS, but most likely won't fix the problem.

6) if vacuum DOES hold, then it is your EVAP canister vent valve.

Let me tell you why I know this issue is most likely the canister vent valve. The valve closes when the car performs the EVAP test. There is a little rubber seal, probably the size of a nickel, that the solenoid plunges forward, closing off the vent to the atmosphere, thus allowing a vacuum to be pulled. What happens is that the rubber seal loses its sealing capability over time or if liquid gas gets to it, i.e., over filling your tank...sound familiar?

What I did was to let the valve soak in AT-205 solvent for an hour to soften the seal back up. I tested the valve w/ 12 volts off the battery to see if it would actuate freely, then reinstalled and cleared the code. My wife drove it to take my kid to softball practice (about a 80 mile round trip). Got a green light on the OBDII!

So a 5 cent rubber seal will cost you hundreds if not thousands of dollars...if you have to take it to the shop, get it diagnosed and then replaced.

Part #: 1644703193 ~$100 on eBay.

eduncanz28

thank you!

eric_in_sd

That's an expensive softball practice. Lucky kid. My 'rents would have laughed if I'd suggested something that far away.

I didn't even bother doing diagnostic and just went straight to servicing the valve. I took the valve out, carefully disengaged the spring, slipped out the little rubber disc, rubbed it with silicone grease, and reinstalled. Also did the o-rings, for no good reason. By far the hardest part was removing enough of the fender liner to get at the valve.

Thanks a $million for sharing the fix.

eric_in_sd

FYI this is the vacuum solenoid under the hood, not the "evap canister vent valve" testing solenoid on the canister.

To add to kcpj.1970's post, you can
(7) test the vacuum and canister by actuating both solenoids and pulling a vacuum with your pump at the line going in to the under-hood solenoid.

PopoySD

I’m trying to tackle this issue..does anyone have the actual part number for this (evap canister vent valve) or a picture of what it looks like? I’ve Googled it and can’t get a definite answer. It looks like it's mounted to a canister and I have to get it out?

I think I found the valve when I checked under the fender liner. But wasn’t sure how to exactly take it out. Do I just pull on it or does it twist out to unlock?

eric_in_sd

It's a quarter turn twist to unlock and remove.

I disassembled mine and cleaned thoroughly and greased the little rubber discs with silicone grease. Reassembled, and 0455 errors no more.

PopoySD

Awesome. Thank you

PopoySD

Is the disassembly pretty straight forward? I was looking at pictures of the valve and I see the o-rings and what not but I can’t seem to tell how the spring and rubber discs come apart.

eric_in_sd

It's straightforward for the mechanically inclined and intuitive. I don't mean to talk down; it's just that some things are obvious when you know how stuff works, but if you don't, it remains a mystery.

I don't remember off the top of my head. I think it had to do with the rubber washer stretching over the center pin.

Definitely also remove, lubricate, and reinstall the o-rings. Be careful with removal to not cut the o-ring. Use dull (no sharp edges or points) metal or hard plastic. You need a good seal on the o-rings as well as the rubber washer.

You could always give it try and buy a replacement if you mess up the overhaul.

PopoySD

Thanks! I’ll give it a shot. I got it off and soaked it in AT-205...I’ll wait a few and then see if I need to take it apart.