Re: PO100 Mass Air Flow / Check Engine Light
OK, first P0100 is a generic OBD-II code for the MAF 101-104 are the specific codes but still OBD. The next layer down are the actual Mercedes codes that will tell you what is really going on but for that you need a scanner that can display them and the least expensive at the moment is the Autel Diaglink with the Benz module (get one free). Next are the Leader CRP123 and the iCarsoft MBII (not the i980). Or a dealer DAS/STAR scanner (are a few in private hands but are expensive).
Since you have the Amazon Bosch MAF (you do have the Bosch and not one of the cheapies ? That is the same one I bought, just is cheaper now), you need to go to the next step and find what is really happening.
Another thing I do is to display my engine parameters with Torque Pro and a cheapie mini dongle. The MAF flow and throttle position are things you can watch and log.
According to the manual "Set Condition: The Mass Air Flow (MAF) Sensor value is less than 16 kg/h when the throttle valve angle is greater than 14° for approximately 5 seconds, or the MAF Sensor reading is greater than a calculated value that is determined by engine speed and throttle valve angle for approximately 5 seconds." and a number of things can cause:
FUSED ENGINE CONTROL RELAY OUTPUT CIRCUIT OPEN
MASS AIR FLOW SENSOR SIGNAL CIRCUIT SHORT TO VOLTAGE
MASS AIR FLOW SENSOR SIGNAL CIRCUIT SHORT TO GROUND
MASS AIR FLOW SENSOR SIGNAL CIRCUIT SHORT TO 5-VOLT SUPPLY CIRCUIT
MASS AIR FLOW SENSOR SIGNAL CIRCUIT SHORT TO SENSOR GROUND CIRCUIT
MASS AIR FLOW SENSOR SIGNAL CIRCUIT OPEN
5-VOLT SUPPLY CIRCUIT SHORT TO VOLTAGE
5-VOLT SUPPLY CIRCUIT OPEN
5-VOLT SUPPLY CIRCUIT SHORT TO GROUND
5-VOLT SUPPLY CIRCUIT SHORT TO SENSOR GROUND CIRCUIT
SENSOR GROUND CIRCUIT OPEN
MASS AIR FLOW SENSOR
POWERTRAIN CONTROL MODULE
Knowing the Merc code(s) can narrow this by a lot.