My daughter hasa 2001 CLK420 with intermitant "Check Engine" light. When I checked the code it is giving meP-0170 Fuel Trim Malfunction, Bank 1 and P-0173 Fuel Trim Malfunction, Bank 2. I am thinking that this is possibly the O2 sensor or the Mass Air Flow Sensor. Any Ideas? Any way to narrow the problem down? Also this engine seems to have two air intakes, does this mean 2 sensors?

 

You have a fuel trim malfunction on both banks. i.e. System cannot achieve required mixture since the system has applied max allowable offset.

This can be caused by either the MAF sensor or the O2 sensors since BOTH contribute to the fuelling calculation.

The problem signature (fault codes) suggests the MAF. You can try cleaning the MAF sensor (lots of posts about this) but to be sure fit NEW OE/Bosch sensor.

However don't rush out and spend your money till you have eliminated the O2 sensors. Need to connect up to an appropriate scanner and observe real time O2 sensor voltage. Is this output cycling correctly and giving expected output. This will confirm that it is the MAF or alternatively increase the chance of it being the O2 sensors.

The other way to confirm that it is the MAF is to get the Long Term Fuel Trim LTFT reading from an appropriate live data scanner. Once +/-30 is reached it triggers the P0170/3 codes.

MAF is usually common to both banks (At least I believe so although I'm not familiar with your 420). O2 sensors are specific to each bank.

Stuart.

 

check crankcase breather hoses going to valve covers,also check rubber seal going to throttle actuator for unmetered air,if rubber hoses are hard replace all of them reset adapation and road test til codes come back