Allion Overheating Coolant Spill

Overheating and coolant spills after a control unit error? That sounds serious! Is the check engine light flashing or steady? Have you checked for diagnostic trouble codes (DTCs) with an OBD-II scanner? The code could help narrow down the communication issue because 'communication fault' can mean many things.

The check engine light is steady. I got a diagnostic trouble code about a communication fault in the control module. What could a faulty connection mean for the overheating and coolant spill?

A steady check engine light and a communication fault DTC suggest an electrical issue disrupting sensor data. The control unit uses temperature sensor readings to control the cooling fan and thermostat. If the connection is bad, the readings could be off, causing the engine to overheat and build up pressure. It could be a defective connection as you suggested, or the module itself. This needs a workshop visit to diagnose and fix. They'll probably use a multimeter to check the wiring and maybe re-flash the module.

Thanks for the explanation. It confirms my concerns. I had the car inspected at a workshop. The problem was a defective plug connection, and the repair cost 95€.