ML430 Fuel Trim Malfunction

[afshinmoshrefi]

I got the CEL on my 2000 ML430 and took it to my mechanic. He read the the code as, Fuel Trim Malfunction, and told me he thought it may be the Catalytic Converter but can't be sure. He told me to take the car to the dealer for diagnosis. When I left the shop, I started gunning the engine, the CEL went off!! This is the second time CEL has turned off after I gunned the engine several times. The car seems to run well except I feel the power has diminished since this CEL has showed up. Any ideas?

[steve32]

Probably the Mass Airflow Sensor. It's a common issue with the MLs and there are many postings related to it. You could try cleaning it with alcohol as the least expensive route, or wait until the dealer pulls the codes. p0173 and I think the other was p0170 were the two commonly associated codes for the MAS. It is a very easy DIY for anywhere from $180 to $250 for MAS. Try a search and type "MAS" or "MAF" and see what you come up with.

[afshinmoshrefi]

Thanks for the info. Checking around the net after your post; your suggestion seems as the stronget possibility. I read some people have successfully cleaned their MAF sensor. Where can I find instructions on how to find and clean this sensor?

[steve32]

Well I will share what I have done, but offer no warranties. The MAS is located between the air filter and intake. It has a plug that runs to the top of your engine. http://forums.mbworld.org/forums/showthread.php?postid=400780#post400780 Unplug it, remove the hose clamp and remove the MAS. Remove the grill cover (honeycombe shape) and then the screen. Small needle nose plyers on the outside of the grill worked for me, so as not to damage the grill. I used ispropyl alcohol and long swabs to clean all the metal parts inside. I also used a degreaser and sprayed the grill and screen cover and rinsed clean. Blow out the excess alcohol on the sensor, and water from grill and screen cover with a mild flow of compressed air. Also clean the male and female ends of the plug. I would let dry for about 30 minutes and reinstall. The check engine light (CEL) could take anywhere around 40 starts or some say 600 miles, to reset. Others have reset it by disconnecting the negative battery terminal for about 10 minutes and reconnecting. Just be aware you will need your radio code if you do this. If you lost it, your dealer can get it from your VIN. I hope this helps. Good luck.

[afshinmoshrefi]

I was able to find it and take it out. It looks very clean.

[steve32]

You might not necessarily see the elements causing the problem. Are you by any chance running a K&N filter? There is much debate as to this filter causing MAF failure.