2002 SAAB 9-5 Engine light is on

Hello and thanks for donating

If the coolant and thermostat have already been eliminated than the next step would be checking the coolant sensor's grounding. Unplug the connector to teh coolant temp. Sensor and connect a test lamp to B+ and pin 2 of the female connector (black). Jiggle the leads and in-line connectors at several places and in different directions to reveal intermittent breaks and short circuits in the harness. Let me know what the multimeter, test lamp or diagnostic tool is showing while you do this. It could be a faulty control module.