My Chevrolet Cobalt Overheats
There’s quite a bit of overheating chatter about this vehicle on tech forums about Chevrolet Cobalt Overheats. If the cooling fans come on, try bypassing the heater core with a length of heater hose. If the problem goes away, you’ve got a plugged heater core. Also, check the hose from the engine to the overflow (surge) tank to make sure it’s not plugged.
If the cooling fan doesn’t come on, check the #1 (30A) fuse in the underhood fuse box. If that’s good, move on to check the relays. There are two relays even though there’s only one fan motor. Yeah, it’s a two speed fan. Both relays are the same part number, so swap them. If the fan works, replace the bad relay.
The power flows from the fuse, to the relays. The relay coils are controlled by the powertrain control module (PCM). Power to the relay coils also comes from the same fuse. The PCM just provides ground to the relay coils.
If the fan still doesn’t work, check continuity on the dark blue wire for fan relay #1 and the dark green wire for fan relay #2. Or, provide separate ground to either of those wires to see if the fan relay closes. Both wires go from the relay box to the powertrain control module. If there’s an open in either of those wires, the relay coil will never energize.
© 2012 Rick Muscoplat