My customer's LS 430 have a problem of speedometer. Although this car stop, the speedometer shows the 30 km/hr. I made a diagnose by Toyota Intelligent Tester II, but i found no fault code. Why this problem happen and how can i repair it.

The little servo motor in the cluster that drives the needle is failing. There are shops on eBay that will replace one or all the servos fairly cheaply, but you have to send the cluster to them to do the work...or you can buy the servo and do it yourself, but then have to recalibrate it. I've had it done on my Envoy which are notorious for failing.

BTW you don't mention the year which can help pinpoint problem areas for that model.