Passat catalytic covertor

Rick P.

Veteran Member
Jul 20, 2002
Barrie, Ontario
'97 Passat, Tornado Red, RIP Feb 17, 2006
Are what look like stainless steel caps at the front and rear of the Passat catalytic convertor really caps that can be unscrewed or are they part of the internal bits that hold the ceramic guts in place?

After spending 7 months with this car's exhaust resonance problem I had the exhaust system replaced with a straight pipe after the cat. As noted in other posts the resonant frequency has dropped to about 1750 RPM which I can live with and even then it is quite mild compared to what it was. I no longer get the low RPM noise I got before or the muffler rattle when shutting the engine off but the exhaust pipe still vibrates. This vibration is transmitted through the mounts to the car. Before cutting apart a new, welded stainless exhaust system after the cat to insert a new flex pipe fix I thought I should rule out a plugged cat. I'm guessing that the two caps cover test ports but thought I should ask before messing something $$$ up.

FWIW, the noise inside the car was and still is 92 dBC when doing 120 km/h (75 mph) on the highway. If anyone with a Passat who also has a sound level meter could tell me what the noise level should be on the C scale I'd greatly appreciate it.



Top Post Dawg
Feb 16, 2000
Santa Barbara, CA
'15 GSW SE 6MT...... '01 Golf GLS 5MT.... '96 Passat Variant....
Those caps cover fittings that held a couple of thermocouples that were part of the "fifth" injector emissions system on '96 Passats. They either weren't used in your market or they have been removed and capped.