What is the comon fault - 1999 Porsche 911 Carrera

The most serious common faults are with the standard 3.4 engine in the early 996 Carrera models (not applicable to Turbo engined vehicles which is a different engine design):

1. The engine cylinder liners develop hairline cracks. (Engine replacement or rebuild required).

2. The intermediate shaft bearings fail in these engines (a well known design fault). Failure requires engine replacement.

3. The rear main seals in the engines fail as exhibited by a slowly worsening oil leak. The seal needs to be replaced when they leak. It's an expensive job.

Problems 1 and 2 are serious have resulted in many engine replacements. Problems 2 and 3 remained when Porsche upgraded to the standard 3.6 engine in the series two 996 Carrera models (problems not applicable to Turbo engines)..

There are a few other issues such as Air Conditioning condensers that clog up with road debris and eventually become porous and fail.