Alfa 166 Cooling Control Module Bug Triggers Overheating

I dealt with a very similar wiring issue on my Alfa 159 3.0 back when it started exhibiting almost identical cooling system problems. Having some experience working on these models, I can tell you these symptoms often point to a compromised data link between the control module and cooling system components. The CAN bus communication error you describe matches exactly what my mechanic found, in my case it was a damaged wire connection leading to the cooling system control unit. The constant overheating and pressure buildup happened because the system wasnt receiving proper signals to regulate coolant flow. The fix required careful diagnostic testing to pinpoint the exact connection fault. Once located, they repaired the wiring and recalibrated the control module. Total cost was 95 Euro for parts and labor combined. Before suggesting more specific solutions, could you share: Build year of your 166, Current mileage, When the problem first started, Any recent work done on the cooling system, Whether the problem occurs more during idle or driving This would help determine if your issue has the same root cause as mine did.

As mentioned in my initial post, my 2007 Alfa Romeo 166 has 148713 KM on the odometer. Just adding that my last service was 3 months ago, which included a routine cooling system inspection but no specific repairs. The car diagnostics suggest severe control unit communication problems. A wiring issue causing data link failures seems very likely based on your experience. Your description of the CAN bus fault matches my symptoms perfectly. Getting similar pressure-related coolant leaks too. The 95 Euro repair cost sounds reasonable if it turns out to be wiring-related. Will have my mechanic check the connections between the control unit and cooling system components first before replacing any major parts.

I see you mentioned checking the control unit wiring, that was definitely the right first step in my case. But given your mileage and build year, theres another potential cause worth investigating that I discovered after my initial repair. The diagnostic trouble code pointing to control module communication can sometimes be triggered by a failing thermostat housing assembly. When mine started acting up again months later, we found the electronic thermostat was sending incorrect temperature data through the data link to the control unit. The system would misread engine temperature, causing the overheating and pressure issues. A new thermostat assembly with updated wiring connections fixed it permanently. That repair ran about 280 Euro including parts and labor. Key signs it might be your thermostat rather than just wiring: Fluctuating temperature readings, Intermittent nature of the overheating, Coolant loss even after pressure testing shows no obvious leaks, Control module receiving conflicting temperature signals Getting a full diagnostic scan focusing on the cooling system control unit communications would confirm if youre dealing with the same root cause.

Thanks for providing those additional details about the thermostat housing assembly and its connection to control module issues. The fluctuating temperature readings and inconsistent pressure you mentioned match my symptoms exactly. The communication fault between components makes even more sense now, my temperature gauge has been showing erratic readings that dont correspond to actual engine behavior. Given these matching symptoms and the cars age, I agree the electronic thermostat could be sending incorrect data through the CAN bus system. Will have my mechanic perform that full diagnostic scan of the cooling system control unit you suggested. The 280 Euro cost for a complete thermostat assembly replacement is higher than just fixing wiring, but still reasonable if it prevents future connectivity issues and coolant leaks. Good to know about checking both the data link wiring and the thermostat assembly itself. Will update once we determine which is causing the control module communication problems in my case.