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Old 04-27-2007, 09:39 AM
blackmercedes's Avatar
Just a guy
Join Date: Dec 2000
Location: St. Albert, Alberta, Canada
Posts: 3,492
Evap emissions system leak - where to now?

My 98 C230 has, once again, a flashing low fuel light and CE light with P0442 and P0445. I've replaced the underhood valve (name escapes me now) and the shut off valve (in the wheel well) and both fuel level sensors, as well as adding a new fuel cap for good measure.

Where to now? I think I've run out of parts to throw at this stupid problem. At least the CE light was off for a while...

John Shellenberg
1998 C230 "Black Betty" 240K

Last edited by blackmercedes; 04-27-2007 at 09:46 AM.
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Old 04-27-2007, 05:35 PM
Senior Member
Join Date: Apr 1999
Location: Walnut,CA,USA
Posts: 554
This is how we do test for purge system leaks we use SDS to activated charcoal canister shut off valve then we remove purge line to regeneration valve and attach vacuum tester with three way hose one way to vacuum gauge one way to purge lline one way to a air condition vacuum pump apply of 25 mbar and pinch vacuum hose "After one minute not more then <5 mbar of vacuum loss" this way you test fuel cap fuel tank charcoal canister,shut off valve and vacuum line in between but not the regeneration valve ! also you can compare intank sensor reading on SDS to your vacuum gauge should be the same. hope this help. if you have more then 5 mbar loss in one minute you have a problem. have to isolate the leaks.
MB STARS Master Guild Technician,17 years MB tech
14 years independent shop owner
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Old 04-29-2007, 08:51 PM
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Join Date: Nov 2006
Posts: 6
My 98 C230 has developed several problems, very similar to above post. P0455 error code Evap Emission Control System Leak (large) and P0170 Fuel Trim. As well as a P0302 misfire. I think these are all related somehow. I do hear a vacuum sound leak near the drivers side front engine compartment (hissing noise) that I do not recall. I have cleaned the MAF. New gas cap. New plugs. Cleaned the throttle body. Any ideas on how to find a vacuum leak? I am not much a mechanic. I read the above post.... but it's like greek Thanks, Dean

1998 C230 (2nd owner) 187K mostly trouble free miles

Last edited by dean2ks; 04-29-2007 at 08:52 PM. Reason: forgot something
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Old 04-30-2007, 12:15 PM
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Join Date: Sep 2002
Posts: 3,068
Follow the vacuum supply line from the purge valve to the engine. If it's not connected properly you will get the P0455 as well as the fuel trim malfunction. It's possible that it could cause random mis-fire codes
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Old 05-30-2007, 10:25 PM
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Join Date: Nov 2006
Posts: 6

Greetings.... Changed the plug wires & boots(right term?) and plugs. Problem sovled with the misfires. Changed the MAF (is it possible that the MAF is bad within a couple weeks?? It's OEM replacement at $260). Gas cap needs replacing (I am certain because the rubber gasket is cracked and was "wet" from who knows what - presumably gas). The car seems to running better than ever with all of these new parts - which is a good thing, and given the very low maintenance levels (except regular oil changes) I have spent less than $600 on maintenance / repairs in 6 years!!! What to replace next to get rid of the very intermittent P170 code (Fuel trim)?

Dean Rogers

1998 C230 - 185K
2000 E430 - 77K

1998 Ford F150 - 120K (watch the V6 in these fords)
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