My son's 2000 Saab 95 SE said engine coolant low so he added coolant. Here it is 2 days later and it is saying it again. When he filled it the first time he saw that there was still some coolant in the reservoir but it was low.. Any ideas how serious it could be?
I would check two things.
1. Is there enough coolant. If there is not enough coolant again you need to check if the coolant is leaking out. You can rent a pressure tester from Autozone to find leaks. It's very simple to use and very effective. It's a radiator cap with a hand held pump attached, you take your cap off and attach the pump. Then pump and listen for leaks (done with car off so leaks are easy to find).
2. Coolant level sensor. If you have enough coolant, yet the light is still coming on then the sensor is bad. The sensor should be located on the reservoir, if you have coolant then it's giving a false reading.