The Volkswagen Engine Diagnostic Code P0101
The good thing about On-board diagnostics (OBD) is that for most cars made after 1990, you can ascertain what is wrong, assuming you have the code book. This will help you or your mechanic start to focus on car repair.
Most Volkswagen's made after 2001 have OBD II, allowing for one to plug in a diagnostic code reader and provide the error codes that triggered the Engine malfunction light on the dash. Usually, until repair, the light remains lit. Many think the engine light is an idiot light to be ignored, this is not the case. Depending on error code from one of many sensors, the car engine may be in limp mode, where the car runs in safe mode to prevent engine damage. Basically, you cannot go much faster than 60 mph or 2200 RPM. Around town, this is not an issue, on the highway, it is.
One common engine code Volkswagen owners get is P0101. Whether it is a gas or diesel, the cause is a Mass Air Flow (MAF) sensor. The sensor is overly sensitive, it seems. If the sensor detects the flow is more than 18% out of spec, it will trigger the engine light. The MAF is critical to all cars, usually located between the air filter and intake, it provides air flow measurements to the car computer, which then calculates the correct amount of fuel for the injectors. If out of spec, performance and MPG is degraded. You might have stuttering, jerking. You might feel that something is holding the engine to slower speeds no matter how much gas is given. Idle may be erratic.
For VW owners of cars made 2005 - 2009, getting rid of the pesky issue is baffling at times. If you have this engine code, possible causes to check are: the MAF sensor (G70 on VW), vacuum leaks after the sensor to throttle body, dirty air filter, ground spots are corroded, wiring or connectors to MAF, check clogged EGR or Intake.
P0101 is an open/short to ground, so your MAF is not getting power, or the wire for Pin 5 is broken. It can also simply mean implausible signal. The G70 MAF sensor should be checked with engine running, EGR valve closed, engine at 1200-2500 rpm, and test for 5 sec. The deviation between actual airflow and model should NOT be more than 18%. The air flow quantity at MAF sensor, at idle, should be 2.00 – 5.00 g\second.
Checking measuring Group 003 with and without basic settings will indicate where the issue is. A low value that correctly tracks the EGR (normal is 270 ON 450 OFF) or engine RPM can mean you have a badly clogged intake manifold.
To check the MAF reference and heater supplies with ignition on:
Pin 2 - ~12V
Pins 3 ~12V
Pins 4 ~5V
Pin 5 to ECM/52 short circuit/near 0 Ohms.
MAF Connector: Pin 1 = temp sensor output, Pin 2 = 12V input, yellow\black for MAF power, Pin 3 = ground (brown) for MAF ground 12V, Pin4 =5V reference input from ECU voltage (Red\green), Pin 5 = Output voltage (brown\blue) MAF signal coming out of the sensor and going to the ECM. Voltage numbers should correspond to the amount of acceleration. Voltage numbers on the multimeter rise smoothly every single time. If the MAF Sensor is good, these readings will not spike up and down crazily but will correspond to the amount of air the engine is breathing at the different RPM's you're accelerating the engine to. If they are not smooth, bad MAF.
The P0101 MAF code issue can quite easily be fixed (sometimes) by cleaning it with 99% rubbing alcohol at an actual cost of $2 and 10 minutes time.
To clean the MAF:
Remove the sensor from the housing and pour about a quarter pint of alcohol into the air inlet of the sensor. Wait about 30 seconds for the alcohol to soften the contamination on the wire and repeat the process. Shake off the alcohol (do not use compressed air unless from a can - computer keyboard/photography). Shop air is often over 100psi and lethal when used for most cleaning operation of this nature. Once the sensor is completely dry, reinstall, clear your code & try it out.
The correct MAF part numbers are: #038-906-461-B(VW) or Bosch#0 281 002 531(Bosch)for the BEW and Mk5 BRM pumpe duse engines.
When testing the MAF using the computer, what you want to see is MAF actual and MAF requested match or be almost an exact match. This means that the sensor is delivering what the car's computer expects. If they are off or MAF actual plateaus, the MAF sensor is bad - replace it. A good ALH\BEW motor MAF sensor should be able to read up to around 850-900 mg/h. The BRM motor MAF sensor should go a little higher because the engine has more power.
The MAF is a very sensitive sensor, which is why troubleshooting and repair is a pain to do. A worn camshaft is known to also trigger this code. Some owners have replaced theirs several times. It is a process of elimination. Make sure the wires and connections are good and readouts are valid. Some owners find the EGR or Intake clogged, Several things trigger this code.