Hello i have a 99 ML320 with 58,000 miles. This is the first time since it was new that the CEL has come on. It came on the other morning when i first started it. Took it to a independent mechanic and the codes came up po170 po173. He ran numerous diagnostics and everything came back fine. He checked the o2 sensors also. He told me that the intake was dirty and said cleaning it may help so he did that and put a new air filter on. The next morning started it up and the cel is on with the same codes. It only seems that it comes on when first started in the mornings then it stays on of course. Im suppose to take it back to him monday morning. Is there any suggestions that i can give him on this. Please any information would be great...

 

Hi,

85% confident it is the MAF.
Characteristic signature including typical mileage at which problem occurred.

Did tech. reset (clear) the codes.

The engine management system is unable to adjust the fuel mixture to the correct setting because it has run out of range which is determined during system boot..
Both cylinder banks = common cause = MAF

but other possibilities exist like O2 sensors.

Hopwever, there are multiple O2 sensors and chances more than one going at the same time is remote (but possible)

Search the site for MAF failure etc. Possibility that cleaning the MAF sensor MIGHT work but only QA solution is a new genuine sensor.

Stuart

 

Okay i actually found a replacement maf sensor here in town and went and installed it and drove it a good 40 or 45 miles and the cel is still on. Will it turn off by it self or do i need to reset the computer with my scanner? Any help would be appreciated

 

it could turn off after so many drive cycles but im sure it will be on for a week or so but it depends on how often you drive it, but you could get it cleared for free at some auto place.

 

thanks for all the help. I used my scanner to reset the codes and drove it a good 50 miles after that and so far it is still off. Im just hoping for the best.

 

I had the same code and problem on a '99, and went through 3 new mafs, and the dealer still wanted to hang more of them on there. Then I found a tech who said he had the same problem, and there is a oil/water separator on some Kompressor engines, and changing that made the code go away instantly. That was a relatively cheap fix. Perhaps the ML engine has a similar part?

 

Kompressor engines are more prone to MAF problems than normally aspirated due to oil that gets into the air intake air due to kompressor bearing lubrication excess / poor seal.
The oil separator is intended to assist in the task of removing oil "mist".

This is why it is a good idea to clean the MAF sensor before changing it for a new one. Your 320 M112 V6 (I think I have the correct engine) is Normally Aspirated.

The 0170/3 code actually identifies that the mixture cannot be changed adequately to satisfy O2 measurements taken by the O2 sensors. The O2 sensors are SOMETIMES at fault so the correct way of being sure is to look at the O2 sensor values and refresh frequency as part of the diagnosis.

Fault codes don't say "Change the MAF". Change the MAF is the experience part of the priocess. The code say Mixture out of range (both banks).

If a new MB MAF is fitted from a sealed box you can be sure that if the problem continues there is an additional fault present.

Yep, normal to reset the CEL Check Engine Light and go for a "blast" and then recheck any pending codes even if the CEL is OFF.

CEL will eventually go off on its own accord after a certain number of cycles but this leaves you wondering whether you have actually fixed the problem for a period of time after the work is done.

OK?

Stuart

 

THanks again guys the ml is running great and its been 100 miles now and no light and no codes.