Radiator cooling fans not operating at temperature

1999 Chevrolet Camaro 3.8 liter radiator fans will not run causing overheating I have tested fan motors tested the relays and fusible links changed out the temperature Cooling sensor what am I missing. could this be a ecu or bcm issue?

The PCM determines the coolant temperature from the coolant temp sensor. From that it decides when to turn the fans on and off, and in which fan configuration, either one fan or both. It controls the fans by grounding the PCM’s cooling fan relay control output pins. If I were trying to debug this, measuring the voltage on those two pins is where I’d start. At least one of them should be close to 0 volts when the coolant is hot enough for the fans to turn on. It might make sense to first make sure the coolant temp sensor is working. While that part seldom fails, should be easy to check.

You may have a fusible link, check the wiring to the fan.

I’ve tested the system with my programmer which has the functions to check fan 1 and 2 it kicks the fans on relays engage so I’m thinking whatever it is has to be before the relays right

Hard to read your sentence without punctuation but… Yes, If you can command the fans ON with your programmer and they run as commanded, then Yes, the wiring is OK. The relays are OK as well. If you can command the fans on, the PCM is probably OK but it seems as though the temp sensor is not OK.

This is a 3 wire sensor, isn’t it? Check all 3 pins of the connector. one should be ground (black wire), if the ignition is on, one should be 5 volts and the other is the signal (usually blue) which shouldn’t show ground or voltage. Bad sensors do happen as does damaged wiring.

Do both fans come on when you turn the A/C on?

If I am not mistaken this was discussed at length before not long ago… like last month? It was a different person with the same car and same issue… and I’m not certain but I do believe they found the root cause and the issue was resolved.

Do a search within this website to find that thread…

Thanks guys for the info put a new temperature switch in it yesterday that’s why I was baffled on this after reading your post I went ahead and bought another temperature switch from a different auto parts store and the fans work thanks really appreciate the info this app rocks


Thank you for the follow up post! Great to know you got it fixed.