I'm getting an intermittent Check Engine light on my 2001 SLK320 (has approx. 36,000 miles). The readout says "P0173 Fuel Trim Malfunction (Bank 2)" with a pending code of "P0171 Fuel Trim Malfunction (Bank 1)". Might that be a MAF problem?

 

In one word. YES! .....but there are other possibilities.
The LTFT reading (>30) will confirm this diagnosis.

Stuart.

 

At the risk of sounding like an idiot
These codes you speak of are obtained where?
What device is used ?
Thanks
Tom

 

Tom,

Not an unreasonably question for somebody who is not familiar with all the tech lingo etc that is used these days.

The codes, known as "on board diagnostic" codes, are obtained from an electronics port / socket usually located in the passenger compartment under the dash or in the engine bay electronics box.

A code scanner (or PC with appropriate softwareand connecting lead) is required to plug into this port and scans the electronic control unit that controls engine ignition and fuelling. Any stored codes will be displayed. The codes are linked to various system faults and give a good starting point for diagnosis. e.g. P0170 = fuel trim malfunction. However the code does not tell why the fuel trim is incorrect.

Readingthe codes is not always a straight forward job (plug in and record display) since different protocols and sockets have been used by different manufacturers over the last 10=15 years. However things are now standardised thanks to the OBDII standard.

Getting the codes read shouldn't be a problem for most garages (small charge 15 mins labour) or you can buy a scanner (and reset tool) for 100 - 1000 USD. Google to discover range / types etc.

Once certain codes are set the CEL Check Engine Light is illuminated to tell the owner to take the vehicle to the garage since the engine emmissions output is likely not in compliance with legislation. Sometimes the light can be on with no apparent fault. However a vehicle will not pass the goverment legislation test if the light is on.

Stuart.

 

Fuel trim errors usually indicate the MAF is dirty.The MAF on your car I believe is just after the air filter, look fora connector and wires coming out of the intake tubing between the air filter and throttle body.Remove it,remove the insert that the connector attaches too (don't know for the 320).Then spray the heck out ofthegold wire at the tipwith CRC MAF Sensor Cleaner (available at places like Pep Boys for 6 bucks). Put it back together, reset the codes with your scan tooland you have a high probability they won't come back. It's a 10 minute job and you don't have to jack up your car.The other possibility is you have a vacuum leak, if you did the car would idle rough. Also the car will run about 92.4% fine with the MAF disconnected. If the car isrunning rough and you disconnect the MAF and it still runs rough, then the MAF wasn't the problem.

Or you can give it to your dealer that will charge you about $650-850 to fix it.

 

Thanks guys.

I replaced the two air filters (which appeared to be originals and were completely clogged) and cleaned the MAF. The "Check Engine" light has been off for a week now, and the engine feels like it has more power, so I think I'm good. I also replaced the gas cap just for good measure. The total cost for a new OEM cap, two filters and some MAF cleaner was about $60. I'm guessing I would have paid a little more at the dealership. ;-)

By the way, the folks at Advanced Auto Parts were kind enough to use their code reader to download the codes for me. I certainly appreciated their help.

 

To confirm all is OK give the cara full throttle 0-60 mph type blast. If you are close to the Fuel Trim limit the CEL will return. If not, then all is likely now oK.

Stuart.