I have an intermittent fault with my stability control.

It came up two weeks ago with a red light that said to slow down and stop engine, which I did.

I then restarted and the light was off. Didnt show up until yesterday again. Same thing, switched off, and it's off again.

Took it to the dealer(I assumed it would be a sensor since it was intermittent..or probably some breakdown in the wiring), as it was off for the entire drive to the dealer.
The dealer is asking me to order parts(which they say they may or may not have to use) to fix the problem. Obviously they would charge for what they used...but I'm a bit skeptical as I thought they would be able to pinpoint the problem and tell me "okay, you need to order 'X' to repair"...and not "you need to order 'X,Y and Z' and we'll just charge for what we use to repair"

anyone have any experience with this problem? I've had a yellow stab control light pop up before and all they did was replace the sensor.