ABS light problem

[Bachonwheels]

I have a 2001 Toyota Vitz (Echo). About 2 weeks ago I vacuumed and washed the car and gave it a good cleanout, as I want to sell it. Like those areas that build up dirt in the grooves next to the handbrake. The very next day when I drove it, I noticed the ABS light coming on. It would come on briefly as you start the car, then goes off, like you would expect. But then it sometimes comes on again before I even start moving, and stays on. If I stop and switch the car off and on again it will then reset most of the time, and then stays off for the entire drive. I have already cleaned the front wheel speed sensors, but left the backs ones, as they seem to be sealed so I guess they may be ok. The other thing I noticed is that since I cleaned the car, the indicator for the gears on the electronic dash, seem to be changing randomly while I drive. Sometimes it shows D for drive in the block, other time N for neutral and other times nothing at all. Could this be related to the problem?

 

[FROSTYBALLS]

Moved to the Yaris club to generate some responses.

[bathtub tom]

Did you use a pressure washer?

[Bachonwheels]

No I haven't. Just a garden hose and a cloth.