Engine warning light when changing gears

[Redbucket Lurker Find all posts View Profile Close Redbucket]

Hi

I have a 2000 manual prado 5vz-fe 3.4 petrol.
When changing gears the engine warning light turns on then turns off when releasing clutch and continuing to accelerate.
Usually happening between 1st to 2nd and then 2nd to 3rd.

When offroad it occurred when going up hills while under power, I've done an oil change and checked the fluid on brakes and power steering. unsure of what this.

Is there a sensor in the gear box for oil?

checked the diff oils and they are fine.

Thanks