Here is a breakdown of what each digit of the code means: First Character - SystemThe first character identifies identifies the system related to the trouble code. P = Powertrain B = Body C = Chassis U = Undefined Second Digit - Code TypeThe second digit identifies whether the code is a generic code (same on all OBD-II equpped vehicles), or a manufacturer specific code. 0 = Generic (this is the digit zero -- not the letter "O") 1 = Enhanced (manufacturer specific) Third Digit - Sub-SystemThe third digit denotes the type of sub-system that pertains to the code 1 = Emission Management (Fuel or Air) 2 = Injector Circuit (Fuel or Air) 3 = Ignition or Misfire 4 = Emission Control 5 = Vehicle Speed & Idle Control 6 = Computer & Output Circuit 7 = Transmission 8 = Transmission 9 = SAE Reserved 0 = SAE Reserved Fourth and Fifth DigitsThese digits, along with the others, are variable, and relate to a particular problem. For example,a P0171 code means P0171 - System Too Lean (Bank 1). To lookup your particular code, visit our OBD Trouble Codes section. P0101 OBD-II Trouble Code Technical DescriptionMass Air Flow (MAF) Circuit Range/Performance Problem What does that mean?Basically this means that there is a problem with the Mass Air Flow (MAF) sensor or circuit. The PCM detects that the actual MAF sensor frequency signal is not within a predetermined range of the calculated MAF value for more than 4.0 seconds. SymptomsYou will likely not notice any serious drivability problems, although there may be symptoms. Possible SolutionsThe simplest thing to do is to reset the code and see if it comes back. Then start with the cheapest, easiest repair procedures: Inspect for the following conditions: An incorrectly routed harness--Inspect the harness of the MAF sensor in order to verify that it is not routed too close to the following components: - The secondary ignition wires or coils - Any solenoids - Any relays - Any motors A low minimum air rate through the sensor bore may cause this DTC to set at idle or during deceleration. Inspect for any vacuum leaks downstream of the MAF sensor. A wide open throttle (WOT) acceleration from a stop should cause the MAF sensor g/s display on the scan tool to increase rapidly. This increase should be from 6-12 g/s at idle to 230 g/s or more at the time of the 1-2 shift. If the increase is not observed, inspect for a restriction in the induction system or the exhaust system. The barometric pressure (BARO) that is used in order to calculate the predicted MAF value is initially based on the MAP sensor at key ON. When the engine is running the MAP sensor value is continually updated near WOT. A skewed MAP sensor will cause the calculated MAF value to be inaccurate. The value shown for the MAP sensor display varies with the altitude. With the ignition ON and the engine OFF, 103 kPa is the approximate value near sea level. This value will decrease by approximately 3 kPa for every 305 meters (1,000 feet) of altitude. A high resistance on the ground circuit of the MAP sensor can cause this DTC to set. Any loss of vacuum to the MAP sensor can cause this DTC to set. If you suspect the condition may be related to aftermarket accessories, refer to Checking Aftermarket Accessories in Wiring Systems.