Brainbox light comes up on the dashboard after driving few kilometres. I change it with another one but still the same problem. Toyota camry 1994 model.

Well, that's the check engine light I think. It is saying something is not normal. You can read out a trouble code to give you an idea of why it is on. Turn the ignition on, but engine stopped, and with a piece of wire bridge terminals TE1 and E1 in the service terminal box, at one rear corner of the engine compartment.

The check engine light will then blink. A steady blink 4 times per sec is "all normal".

Trouble codes are 2 digits, and these will be blinked - first digit - pause - second digit - repreat.

So the oxygen sensor fail code (a common one) is 21, and will show 2 blinks - pause - 1 blink - repeat.

There are 22 of these codes