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Monday, September 6, 2010

Air Mass Sensor on VW 2000 Passat, How to Test

First, different names for the same component, Air mass meter (AMM), Mass Air Flow Sensor (MAF). MAF is the accepted name.

The purpose of this device is as its name suggests, measure the amount of air going into the engine. The units used to measure this are Grams(mass) per second (g/sec). This is one of the main inputs the engine computer uses to determine the amount of fuel to inject into the cylinder.

So the check engine light (CEL) is on, on your VW and your car is not running right. VW has a history of problems with MAFs and you check online and everyone suggests cleaning or replacing it. You do that and the car is not now what!

Proper diagnostics of a MAF fault involves the use and understanding of a good scan tool. The primary values to look at are: g/sec of the MAF under different engine loads, long term and short term fuel trim values. Using the values you can determine if the problem is the MAF, poor connection to the MAF, a vacuum leak, exhaust leak, injector or fuel pressure problem. The other advantage of using a scan tool is after the repair is done and after a short test drive you can verified the problem is solved.

Throw parts at it for common known failures; makes you look like a genius when you guess right, but can be expensive when you guess is incorrect. At Metric Wrench we are equipped and trained to solve problems and eliminate the guess work.

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