BullSae

Hello, I am new here with no technical background and need your advice. My wife has ’99 ML320 with about 40K miles on it and had all scheduled maintenance. Have had no problems whatsoever until Chevron gas station service man filled up the gas tank with 87 by mistake. (Until then I’ve used Unocal 76 premium). Within a mile of driving, CEL came on for the first time but had no choice but keep driving (we were on vacation in country side) but went off after 4-5 hours. A few days later, we filled up the gas at Texaco and CEL came back on again in a few minutes. Since then, it stays on. After some research through this forum, I learned a lot about CEL but couldn’t narrow down my problems. Autozone checked OBD code: P0170 & P0173 (Fuel Trim Malfunction) and they couldn’t erase the codes, but on the way home it went off but came back on again after I got Chevron gas on the same day. Since then I only use 76, but CEL is still on. I erased the codes two times by disconnecting battery but came back on in 2 days each case. Is my case related to the gas? What could be the problem in my case? What are my options (Dealer would be my last option)?? Is it true only dealer can erase P0170/0173? I would really appreciate your advice. Thanks and sorry for making the short story long (??)

awiner

Usually P0170 and P0173 mean your Mass Air Flow Sensor took a crap. However, it can also be caused by vacuum leaks, etc.

My guess is the MAF. How many miles on the ML ?

Any CEL codes can be erased. They will come back however if the problem is not fixed.

BullSae

Thanks for your feedback. It has 40K miles. I assumed MAFS could be the one based on treads about CEL but was not sure. If it is, what caused the MAFS mulfuction? Is actual sensor circuit (inside) broken? If I replace it by myself, what would be the next step - do I need to reset anything other than CEL by battery off?

awiner

The MAF uses a hot-film type sensor inside of it. They go out more frequently than they really should. Many people have complaints about them if you read the forums.

They are easy to change out but you really should have the dealer re-set the adaptations via the Star Diagnostic service computer afterwords or at least ask them if the re-set of adaptations is necessary for your vehicle.

Looking in the WorkShop Information System for the ML, it doesn't state anything about have to set adaptations. But I know with many models you do.

BullSae

Thanks so much for your infor. I will read the forums more this weekend and ask the dealer if it is necessary. Thanks!

13benz

same code was thrown on my 98 c-class and yes it was the airflow sensor. air filters letting junk get by them is what i have heard kills them, having the dealer replace mine and reset the values was about 400 bucks.

BullSae

Is dealer re-set of adaptations a “must” or just “preferred” or “not-necessary”. I asked to two service advisors at the same dealer but different answers…one said “must” and the other said “better to have”. ($395 for the sensor and $95 for the re-set). Confused again so I had put this issue aside for a while. But I will need to replace it anyway (hate to see the light so I covered with my biz card - funny). I plan to replace it by myself if it is not required. Any comments?

BullSae

Three days ago, engine misfired (for no reasons?) when I started the engine in the morning , so I turned the engine off and on again. It was fine then and CEL light went off. Three days passed and came back again this afternoon after I filled up gas. I just noticed that it comes back on after fill up the gas tank. Any ideas ???

BullSae

FYI,
just after my last thread, this is what I did that night: cleaned the MAF & its female/male connectors (learned from another Forums but just tried) and gas cap & rubber ring (and I flipped over the ring) with electronics cleaner and replaced air filter with a new one. Since then it did not come back on. So I am not sure what I fixed but it's gone now about a week.

Ash001

Hi I am new to here, have 1998 C230 with 74K miles and have got the CE light on. The code check was P0170
'Fuel Level Trim Malfuntion Bank 1. Recently I had checked the air filter and this came up soon after with 20 miles. Have got it erased 2 times but comes backup in within 25 miles. Reading from above seems like it could be MAS. Should I try to clean it up or replace it altogether.

mercedestech2

I'm a dealer tech, and with a p0170 and p0173 98% of the time the problem is a mass air flow. In regards to the question about having the adaptation values reset, it is not needed, they will come down automatically over time as the car adapts to the new data being sent by the mass air flow sensor that works properly. Many dealers charge for reseting adaptations because it does a number of things, it shows the tech the repair is correct much faster than letting it come down on its own. Also, when you reset the adaptations, the codes set in ME are erased at the same time.

StapleGun

My 1998 C43 produced both those codes...it was the MAF. Purchased it on ebay (Bosch) for $203 including shipping. Adaptation values were never messed with and the car now runs like a top.