I recently purchased a 1995 Pontiac Bonneville SSE. A prior owner had replaced one of the radiator cooling fan relays with a jumper wire. This resulted in the fan running whenever the ignition is in ‘run’. I have replaced the relay and the socket (the jumper partially melted the socket). My question is: How can a ‘backyard mechanic’ test to be sure the computer is activating the fans when it should? If it will support your answer, I have a subscription to Alldata DIY for the vehicle and can view TSBs and service info on that site.
The thing to do is measure the engine temperature and see if the fans come on as specified. The specs are right fan and low speed left fan at 212’ F, high speed left fan at 226’.
If the car has a temp gauge that works properly, you can use it as a rough guide. Better is using (properly) an infrared thermometer to monitor engine temp. If the engine coolant temp sensor is working properly, then the engine temp can be read from the computer with a scan tool.
I don’t expect a backyard mechanic to have a scan tool. Most probably don’t have an infrared thermometer, but perhaps should. I’m not aware of an alternative way to accurately and reliably determine engine temp.
Nevertheless, if the fans come on, then go off, and the engine isn’t overheating, it’s a pretty good bet everything is fine.
Putting newspaper over the front of the car (covering just the grill area where air flows into the radiator) will cause the engine to warm faster (handy in cold climates). Doing that will make it easier for your engine to warm up so you can get an idea if the relay’s working or not.
The temperatures are what I really needed. No, I don’t have a scan tool or an infrared thermometer. Lack of the tools is what I meant by ‘backyard mechanic’. My brother, aka the family mechanic is an electrical engineer that worked as a mechanic in college. We just didn’t know for sure when the fans were supposed to be on.