Q: How to troubleshoot the Coolant Temperature Indicator System and the Engine Coolant Temperature (ECT) Sensor?A: The coolant temperature indicator system includes a dash warning light or gauge and a coolant temperature sending unit on the engine. The Engine Coolant Temperature (ECT) sensor also acts as the coolant temperature sending unit. If overheating is indicated, check the coolant level and ensure all wiring connectors are secure. The indicator light should come on when the ignition is turned to START, showing the bulb works. If it doesn't, the bulb may be burned out, the ignition switch faulty, or the circuit open. The light should go off once the engine starts unless it overheats. If it stays on, check for trouble codes in the Powertrain Control Module (PCM). If overheating is frequent, check the coolant type and concentration.