Buick Engine Overheating Linked to Control Unit Fault

I had nearly identical symptoms with my 2004 Buick LeSabre last year. Have some experience working on cooling systems, but needed professional help for this particular issue. After seeing similar symptoms, engine overheating, coolant loss, and control module communication errors, I took it to a workshop. The diagnostic trouble code scan revealed a faulty wire connection between the engine control module and the cooling fan control unit. The CAN bus system was reporting incorrect temperature readings due to this damaged connection. What seemed like a major cooling system failure was actually just a damaged cable and connector. The repair involved replacing the wiring harness section and securing proper connectivity. Total cost was 95 Euro for parts and labor, which was much less than I initially feared when seeing those symptoms. Before suggesting specific solutions, could you share: Which Buick model do you have exactly? Are you noticing any patterns when the overheating occurs (highway vs city driving)? Does the cooling fan activate at all? Have you checked if coolant is actually reaching the radiator? This information would help determine if your issue matches what I experienced with the control module communication problem or if it might be something else.

Thanks for sharing your experience. My Buick Royaum has 66065 KM and was last serviced 3 months ago. The cooling fan does activate intermittently, but not consistently as it should. When checking the radiator, I noticed coolant flow seems restricted even when the engine is warm. Checked the wiring near the control unit connections and found some corroded terminals, which might explain the data link communication issues showing up in the diagnostic trouble codes. Going to clean the connections first and recheck the codes before deciding on next steps.

Thanks for the update on your Royaum. When I dealt with corroded terminals on my Buick, cleaning them provided only temporary relief. The communication fault kept returning after a few weeks because corrosion had actually spread deeper into the wiring than was visible. The restricted coolant flow you mentioned matches my symptoms too. However, in my case, the software glitch from the faulty wiring was causing the thermostat to malfunction, creating that restriction. The control module was getting incorrect temperature readings and not properly managing the cooling system. Looking at your description, you might be facing a compound issue like I did, where the wiring issue is causing both the control module communication problems and improper cooling fan operation. While cleaning the connections is a good start, you might want to: 1. Check the wiring harness for any signs of damage beyond just the visible terminals 2. Test the thermostat operation specifically 3. Monitor if the control module receives accurate temperature readings after cleaning If the diagnostic trouble codes persist after cleaning, replacing the affected wiring section might be necessary, just as it was in my case. Would you be able to check if the temperature readings on your scan tool match what the gauge shows? This helped identify the extent of my wiring issue.

Thanks for the detailed suggestions. After cleaning the terminals, I hooked up my scan tool and found the temperature readings still fluctuate wildly compared to the gauge display. Looks like you were right about deeper wiring issues. The diagnostic trouble codes still show CAN bus communication faults even after cleaning. I traced the wiring harness and found significant wear near the firewall where it flexes. Going to replace that section of the harness and the corroded connectors. The thermostat seems to respond when tested directly, so I'm confident the control module communication problem is the root cause, affecting both the cooling fan operation and temperature monitoring. Will follow up after replacing the damaged wiring to confirm if this resolves both the connectivity issue and cooling system operation. Really helpful to hear about your similar experience, saved me from unnecessarily replacing other cooling system components before fixing the actual control module communication problem.