I was recently reminded by our good friend Fujisan that as some 4.3s will be due for the first MOT this year that it might be a good idea to review this subject and I will pin it for future use.
The VSC is such that if you use conventional means to test the brakes (brake roller tester with one wheel being tested at a time) it will pick that up as the vehicle out of control as one wheel is turning and three are not. The system cannot detect that the vehicle is stationary because there is a speed sensor on each wheel (used for vehicle speed detection rather than ABS operation - very unusual). The one turning wheel will fool the system into thinking that the vehicle is in motion. For this reason the VSC MUST be disabled otherwise when the first wheel turns in isolation from the others it will try to lock up the transmission in 4WD and the brake tester will force the wheel to turn against the locked transmission. Serious damage could result as you will be trying to haul a ton and a half of RAV out of the brake roller by one wheel against partially applied brakes because the tester is pressing the brake pedal!!! It is a potential RAV transmission/VSC infighting thing!
A main dealer should know what has to be done and will install his DLC3 tester and set it to "brake test" which will disable the VSC/Traction Control. However, I for one will not be going to the dealer for MOT (purely as a matter of convenience) and if anyone else has similar plans then the VSC has to be disabled. It is extremely risky to assume that the independent tester knows about this very unusual system and wouldn't just go ahead and test it in the normal way. There are three ways to ensure the test is conducted without risk. You personally don't have to do it yourself but it would be wise to print this out and take it to the MOT station and make sure they are very aware. Here are the three methods;
1. Use the press brake/hand brake method described here;
Begin with the parking brake off and the engine off.
Apply parking brake and press the foot brake twice then let the parking brake off again.
Press the foot brake and pull the parking brake on and off twice then let the foot brake off again.
Finally pull the parking brake on and press the brake twice.
The VSC light will now come on and stay on until you switch the ignition off again after which the VSC defaults to on again.
2. Use a piece of wire to short out the pins 4 and 12 of the DLC plug shown here;
Here is a photo of the plug just by the bonnet pull;
3. Raising the vehicle off the ground
Then there is this method but it is labour intensive and the MOT tester isn't likely to thank you for it! It requires the other wheels to be allowed to turn while the individual brakes are tested (albeit fail safe as no damage can be done). It means the car has to be lifted to get the remaining wheels off the ground and the handbrake off so that all wheels can turn freely when the transmission locks up - like this;
Remember that this also has to be done when testing the rear wheels and the tester is going to love that too! The easiest way is in disabling the VSC as described in either 1. or 2. above. The first is easy enough with a bit of practice and the second needs a bit of confidence but is also easy. I printed the first procedure and left it in the glove box. Just remember that when taking the car for test to have it disabled and don't worry - the first time the ignition is switched off the VSC will reset itself so do that before leaving.