Q: How Do You Diagnose and Replace a Faulty Coolant Temperature Gauge or Sending Unit on Toyota Supra?
A: If the coolant temperature gauge isn't working, check the fuses. If the gauge reads hot on a cold start, disconnect the wire at the coolant temperature sending unit. If the gauge drops, replace the unit. If the gauge doesn't show up after warming up, detach the wire at the unit, connect it to clean ground, and switch on the ignition.