Hello everybody,

the Check Engine Light of my '99 ML320 is on again (after I replaced the Mass Airflow Sensor). Now the error codes are:

P0173 Fuel Trim Malfunction (Bank 2)
P0170 Fuel Trim Malfunction (Bank 1)
P0700 Transmission Control System Malfunction

Any idea about this problem with the transmission? Any history? What can it be? What could be the solution?

Thanks in advance,

Francesco

 

they reset the fuel adaptaion too?

 

Hi Sleepwalker,

I borrowed the ODBII scanner at Auto Zone and did the reset myself. Is there anything I'm missing? How can I reset the fuel adaptation?

Now the P0700 Transmission Control System Malfunction error is gone.

But I still have PO173 and PO170. I reset them and the Check Engine Light goes off but comes on again after a few miles. I recheck with the scanner and each time it's PO173 and PO170. I reseted several times now, but the light always goes on after a while.

I checked again the report written by the dealer when they checked the car during last service and it reads:

Tested Mass Air flow sensor and verified 5V sing al nominal. Checked actual value of Mass Air Flow sensor k/o voltage and found 1.4 volts not nominal. Mass Air Flow sensor is faulty.

What does that mean?

Thanks again for you help,

Francesco

 

Hi again,

I just scanned the codes again with the ODB II and these are the results:

PO170
PO173 (as usual)

New codes:

PO110 IAT Sensor Circuit Malfunction
PO100 MAF or IAF Circuit Malfunction

I personally changed the Air Filter 500 miles ago. What's happening to my car? When I drive it looks OK... But this Engine Light On and these codes are driving me nuts...

Thanks again,

Francesco

 

Eresed the codes again, drove 40 miles, Check Engine Light on again. Now codes are the usual 170 and 173. I believe the answer is in that "verified 5V sing al nominal. Checked actual value of Mass Air Flow sensor k/o voltage and found 1.4 volts not nominal".

Any suggestion on how to solve it?

Francesco

 

one thing you have to look for is a vacuum leak that will cause this po170 173 to keep coming on again and again. it is the biggest mistake that people make when replacing these items

 

Thanks vytamenc.

I checked again and the MAS is firmly installed. How can I check a vacuum leak? I searched the web and found the following, can you confirm this is what you mean?

"The best method is to go to the Auto Parts store and get a can of Starting Fluid. This is basically Ether. This is a very volatile substance that is easily sucked into a leak and causes a dramatic change in engine running condition.

With the car at idle spray carefully around the base of the carb or throttle body, at the area where the manifold meets the head, around vacuum hoses and any connections either below the carb base or after the Mass Air or Air Flow Meters. Any noticeable change in idle speed or quality will indicate a vacuum leak".
Thanks,

Francesco

 

yup this is a good way to check for them. ansl pull off the black plast cover over the engine compartment you will hear a major leak if there is one. look at all the hoses under the hood make sure they all go somewhere i am willing to bet it is a hose towards the back of the motor on the left side search really good spend a hour or so looking.

 

Ok , but what do you think about this:

Tested Mass Air flow sensor and verified 5V sing al nominal. Checked actual value of Mass Air Flow sensor k/o voltage and found 1.4 volts not nominal. Mass Air Flow sensor is faulty.

Don't you think is actually the whole ECM that is faulty?

Thanks,

Francesco

 

did you check it with the ignition off or on. off hould be 1.2 i think on should be 5. trust me check for vacuum leaks i see it all the time very unlikley that it is the m.e. control unit. m.e. control units are covered under 8/80 warrenty at least in california they are