2008 Silverado overheating problem

I have a 2008 Silverado 1500 work truck that has started to give me overheating issues. I have narrowed it down to the electric fans not kicking on unless the A/C is on. I know this is generally a relay issue, but a friend of mine told
Me there is also a switch by the thermostat on the block. Is there such a creature or should I concentrate on the probable relay? I miss old fashion fan clutches.

I don’t know of any switch, and the electric schematics don’t show a switch.

The three cooling fan relays are controlled by two ground circuits from the ECM. If both fans are working properly with the A/C, in both low and high speed modes, then the relays aren’t the problem. If both fans don’t run in low or if one or the other doesn’t run in high (with A/C), then there could be a problem with a fan, a relay, a fuse, or the wiring.

Assuming both fans work as they should with the A/C but not at all based on engine temperature, the ECM may not be receiving a signal that the engine temp is high enough to trigger the fans. If that’s the case, the problem could be in the engine coolant temperature (ECT) sensor circuit. Could be a bad connection at the sensor, a bad wire, a bad sensor, or something wrong with the ECM ECT signals. Does the temp gauge in the dash seem to work okay? Is the CEL on?

1 Like

$10 to replace the Coolant Temperature Sensor.

The temp gauge work fine. That plus a light antifreeze smell brought my attention to the matter. There is no CEL at all.