2003 Passat GLS Wagon emits loud hissing sound

Asked by Jul 23, 2010 at 10:25 PM about the 2003 Volkswagen Passat GLS Wagon

Question type: Maintenance & Repair

The sound sounds like high pressured air being released like the air brakes on a tractor trailer, but it goes on for 4 or 5 seconds. It only happens when I start to drive after the car has been fully cooled down. The loud hissing stars after I have driven about 25 yards. What's going on?

1 Answer


This is most likely the SAP or (Secondary Air Pump). All VW/Audi cars have the same pump which was installed for emissions starting somewhere in the 90's. On the "newer" ones, the rivets break loose and the pump begins to leak and become VERY loud in some cases. The pump will only turn on immediately when you start the vehicle after it has been parked overnight and it will come on from time to time until the car is fully warmed up. NOrmally it is quiet and you can barely hear or feel it running. All it does is send unburt gas vapors through the intake pipe to make sure they get burned up. THe cost for replacement is high at a mechanic. If you have a few hours and can do the work yourself, check out this VW FORUM SITE for the Do It Yourself. VWVORTEX.COM/Forums. I have fixed one of these pumps and it was very easy to drill out the rivets and reseal the sucker with bolts and locktight. Just getting to the pump and replacing it was the long part. Good luck.

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