toyota avensis timing belt or chain

According to Wikipedia.org, the engine is a 1ZZ-FE, which is chain driven. To cross reference (for accuracy's sake here in the States), the 2006 Pontiac Vibe uses the same engine. It, too, shows a chain.

Usually, a chain is good for the life of the engine, so there should be no reason to change it. In the case of the 1ZZ-FE engine, sources are saying it should be good to 300k miles (~483kkm) as long as it has proper maintenance (mainly ensuring oil is changed on time) and the engine isn't abused. The tell-tale sign is noise. If you start hearing a lot of noise coming from where the chain resides, it's time to change it.

If it goes out, you'll lunch th engine. Changing one out is about as involved as changing out a timing belt. It does take some work and is not going to be cheap.