ML320 P0300,P0304,P0305 codes - Mercedes-Benz Forum

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post #1 of 7 (permalink) Old 02-12-2009, 06:38 AM Thread Starter
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Unhappy ML320 P0300,P0304,P0305 codes

Hi, I live in the UK and have a yr2000 ML320 with about 80,000 miles, sorry for the long post but a bit of background info may be helpful for someone to suggest ideas - Over the past year the truck has become pretty "sluggish" especially noticable when it faces any hills (speed drops doesnt matter what you do with the accelerator). Adding to this from cold I now have to start the truck (starts first time everytime! and always has) and let it idle for about 2 mins before putting it into drive, if I select D straight after starting and try to drive off it judders, hesitates and is totally undriveable - only way to get it back into action from this point is to turn the ignition off and back on again - as I dont use the truck everyday I've learned to live with the above (at this point the engine light has never been on once)....

However things have just got a whole lot worse - I'd not used the truck for a week or two so thought I'd take the battery off and give it a charge, put the battery back on the next day and O NO, truck starts first turn of the key but then revs drop down to 400-500 where it sounds like its running on 1/2 the cylinders and it either stalls or idles at very low revs (occasionally jumping up to 1,500 revs on its own before going back down) touching the accelerator doesnt seem to have much effect, other than stalling it sometimes. Engine light is now on so read the codes and initially it had P0300, P0304, P0305, P0306 if i'm right thats the 3 cylinders on the right looking from the front? with misfires, no other codes also what I can hear is what sounds like a "stone" rattling around in the cat area of the exhaust on that side (this rattling has been around for a while - not just since the battery was removed/charged), not sure if this is related in any way?. Cleared the codes and restarted a couple of time and codes still read pretty similar P0300, 304 and 305 now. I dont use the truck all the time and not in a position to spend £££'s on it at the dealers, any advise would be more than appreciated, if you've not fell asleep reading all that !!, sorry

Couple of other things, air filter, spark plugs, oil changed about 8 months back but initial problems were apparent before and after that point
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post #2 of 7 (permalink) Old 02-12-2009, 08:11 AM
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Need to check exhaust back pressure on both banks. Codes you are getting are for left bank or bank 2.

Tip. To determine which is which look at front or rear lamps. One has letter R, other letter L. :-)

1972 280SEL 4.5
1999 ML320
2000 E320
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post #3 of 7 (permalink) Old 02-12-2009, 08:51 AM
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hi, i had the same codes, changed the MAF sensor and the codes were gone as well as the check engine light.
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post #4 of 7 (permalink) Old 02-12-2009, 10:44 AM
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Sounds familiar. Here is my post from a couple of years ago. My catalytic converter on that side was plugged:

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post #5 of 7 (permalink) Old 02-13-2009, 04:49 AM Thread Starter
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Thanks for all the quick replies, I'll start with getting the back pressure checked as its not a big job, although I've not got the equipment to do it myself so will have to work out a way of getting it to a garage!. Looked at a loads of posts about the MAF and many people say they have replaced and its not fixed the problem so dont want to go spending ££ just yet, although thanks for the advise Da80... it will probably be the next thing I change in the list to get this resolved

I'll update as soon as I get the checks done, thanks again
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post #6 of 7 (permalink) Old 05-22-2009, 02:36 AM Thread Starter
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Just to close the loop - the problem was just the MAF sensor (guy at the MB Independant garage had a spare one he put on to test before I parted with ££), replaced and runs like a dream again, hopefully it was that causing all the problems I had. Sorry for the delay in updating
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post #7 of 7 (permalink) Old 05-22-2009, 03:45 AM
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Many thanks for posting back your eventual solution Rob.

Imagine the problem being just the MAF sensor and not actually triggering the usual MAF related codes of P0173, P0174, P0100 or P0110 - Maybe the experts will explain that later.

I had to say I too thought it was your catalytic converters - Which are a very expensive fix.

I'd say your independent garage/mechanic saved you loads of cash!
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