My 1999 Toyota Previa 4x4 (0nly 70,000 miles) has been regularly serviced and kept in good order. Last week the ABS warning light lit up and remains on whenever the car is being used. My regular Toyota garage checked it and reports that all four sensors and the control unit need to be replaced. Two very experienced Toyota mechanics tell me that such a wholesale failure is unique in their experience. Am I right to seek a second opinion?

SOURCE: Toyota Vitz 2003: (ABS and HandBrake warning light constantly on)

this is a common first sign of your antilock brake computer failing. You will most likely never feel a difference in your car but there is a slight chance all your safety features will not operate properly in a collision.

SOURCE: Rattling noise when the car idles in drive/reverse position or...

predetonation,called ping can result from poor quality fuel,and high outside air temperature,it happens at lower speeds under load. a rattle could also be from the heat shield around the catalytic converter,it would buzz more if you wer idling and turned up the fan,the fan pulls quite a bit of current,and tha a/c will load the engine a bit.

SOURCE: Toyota 4Runner/maintenance schedule at 140K miles

The maintenance schedule is an outline and should be followed if you want to keep your vehicle in good condition. the maintenance items listed in the schedule are performed at their set intervals for a reason. Manufacturers have found the wear limits on certain parts and those parts may need to be serviced or replaced at those intervals or catastrophic failures may result.

SOURCE: ABS LIGHT ON / BAD WHEEL SPEED SENSOR / HOW TO REPLACE

You can do it yourself. One bolt. Check the plug and wires before you replace the sensor. A stick or whatever can break a wire and the sensor reads bad, but really it just needs a wire. Worth a quick look before you spend the $ on a new part.