Why won't my radiator fans come on when vehicle is hot?

LOVEREALITY1014

MEMBER
2002 BUICK RENDEZVOUS
98,000 MILES

At this point I am clueless. The vehicle has plenty of antifreeze in it and has been "burped" so there is no air in the system. When the vehicle gets hot enough that the fans should kick on they don't. We know that it's not the fan motors bc they work when they are grounded to the battery. As long as the fans are grounded so that they stay on the engine stays cool. We have changed the temp sending unit to the radiator fans and checked the fuses also. What else is left? I need help Thanks

1 Reply

CARADIODOC

MECHANIC
33,916 POSTS

Did that sending unit have one or two wires going to it?

You need to find a mechanic with a scanner that can display live data to see what the Engine Computer is seeing. If it sees less than 220 degrees, it won't turn on the fan relay. Most scanners are "bidirectional" meaning they can be used to command the various computers to do things. You can select "radiator fan relay", then listen and feel if it is turning on. Some are electronic but you can still see the results when it is commanded on. If the fan motor is tight it will run but draw excessive current and can blow a fuse or fuse link wire. You can determine that by measuring for battery voltage on one terminal of the relay.