Help please. Amber light for tyre pressure has been on for ages. Was told by garage, rear tpms sensors not working. Bought new ones, replaced today. Light still on. Flashes when the car is started then goes solid. I borrowed a reset tool and the light went off. Now when I start the car the light comes on and stays on. No flashing. I checked pressures and drove for 20 minutes as suggested. No change. What can I do please? Driving me mad and an mot fail.