In order to test your MAF, O2 sensors and catalytic converter, check out the following blocks in the "Engine" control module with your VAG-COM. Blocks 002, 030, 032 and 033 are done in "Measuring Blocks" while blocks 036, 034 and 046 are done in "Basic Settings". Let me know if you have any questions about how to run the tests. (NOTE: The following tests are MKIV VR6 specific. If you have a 1.8T or 2.0 engine, the procedure from running the automated tests is slightly different. For a 1.8T engine, see this THREAD for instructions on how to initiate the tests. I'm not positive about the initiation procedure with a 2.0 engine, but from what I've found, with an AEG engine you manually raise the engine speed to between 1800 and 2200 RPMs, and with the AVH and AZG engines, you derpress the accelerator to the WOT (wide open throttle) position to raise the engine speed to ~2000 RPMs.

Block 002 - Load Registration

- Check the MAF airflow reading at idle. Make sure the car is running and warmed up and the A/C is off. Go to Block 002 and look in Field 4. The value at idle should be between 1 and 25 g/s. If it's lower than 1 g/s, then there is probably a leak in the intake tubing between the MAF and manifold.

Block 030 - Oxygen Sensor Regulation

- Go to Block 030. Field 1 is a three-digit binary code which gives the status of the pre-cat oxygen sensor. Field 2 is the same thing but for the post-cat oxygen sensor. The digits indicate whether or not the sensor heater is working and whether or not the oxygen sensor control is operational and active. The value should fluctuate between 111 (heater on) and 011 (heater off). The last two digits can also fluctuate between '1' and '0', but should be predominantly '1'.

Block 032 - Oxygen Sensor Control Learned Values

- Go to Block 032. Field 1 represents the fuel trim at idle (additive) and Field 2 represents the fuel trim at part load (multiplicative), i.e., while driving. The value should be between -10 and +10% (negative indicates the engine is running rich and positive indicates the engine is running lean). If the value is close to +25% (which is the upper limit), it usually means that the MAF is bad. If the value is somewhere betweeen +10 and +25%, it could mean that the pre-cat oxygen sensor is bad, there is a leak in the intake or that the MAF is on it's way out. The value I found for my car (VR6), which has a new 2.0 MAF and new oxygen sensors is +1.6%.

Block 033 - Pre-Cat Oxygen Sensor Control

- Go to Block 033. The value in Field 1 represents the pre-cat oxygen sensor control. The value should fluctuate at least 2% in the -10 to +10% range.

Block 036 - Post-Cat Oxygen Sensor Control

- Go to Block 036 (this test must be done in basic settings, not measuring blocks). Depress and hold brake pedal to run the automated test. The engine RPMs should raise to around 1400. Field 1 is post-cat sensor voltage. It must fluctuate slightly between 0 and 1V. Field 4 will say either 'TEST OFF/ON' before/while the test is running and either 'B1-S2 OK' (sensor is good) or 'B1-S2 NOT OK' (sensor is bad) after the test is finished. Release the brake pedal after the test finishes.

Block 034 - Aging of Pre-Cat Oxygen Sensor

- Go to Block 034 (this test must be done in basic settings, not measuring blocks). Depress and hold brake pedal to run the automated test. The engine RPMs should raise to around 1400. Field 1 is the engine speed. Field 2 is the catalytic converter temp. Field 3 is the value which tells you how aged the sensor is (not sure what it's called). Field 4 will say either 'TEST OFF/ON' before/while the test is running and either 'B1-S1 OK' or 'B1-S1 NOT OK' after the test is finished. The aging value must be above 0.80. The value for a new sensor is 1.99. The value will decrease as the sensor ages. Release the brake pedal after the test finishes.

Block 046 - Catalytic Converter

NOTE: The test in Block 034 must be done just before this test or it will NOT initiate!

- Go to Block 046 (this test must be done in basic settings, not measuring blocks). Depress and hold brake pedal to start the automated cat. test (last approx. 100 secs - the cat needs to be warmed up above a certain threshold for an accurate reading - the threshold is usually 400°C). The engine RPMs (Field 1) should raise to around 1400. Field 2 is the cat. temp. This will also rise during the test. Field 3 is the cat. conversion efficiency. If the cat is good, the value should be below 0.50 at the end of the test. Field 4 will indicate if the cat is good (CAT B1 - OK) or bad (CAT B1 - NOT OK). Release the brake pedal after the test finishes.