Cooling Fan not Engaging Unless AC Is on 2017 Sonic 1.8 Hatch

[Irishbear]

Hey all my fiance's 2017 Sonic 1.8 cooling fan is not engaging.

Last week she got an overheating warning, since then I've replaced the thermostat with a new one. The fan was not engaging at all even with the AC on. I swapped one of the 40 AMP fuses (square ones) out and now it engages with the AC on but not if it's off. Using an ODB reader, the temperature gets up to about 230 and I shut the car off.

Someone advised that a faulty temp sensor in the radiator on the passenger side could be causing the issue, I'm going to replace all the fuses and relays today (multimeter died so I can test them). Could that temp sensor cause the fan to not kick on? Tracing the wiring harness it's connected to does lead to the fans power outlet. I'll warn that I'm not really a mechanic, and only use what I can find online to fix something. Also if its relevant the radiator is putting liquid into the reservoir after its started.

 

[SuperS13]

I had the same issue for my 1.8L it's the cooling fan its self. There is a resistor on the passenger side in front of the cooling fan assembly. Just get a dorman fan with the shroud plug it in and you'll be good. My issue was my radiator fan wouldn't kick on unless you either turned on the blower motor with heat or ac. The resistor is the issue as it can short out and corrode from the elements. It's a known problem...get a dorman one on rockauto for $140 and you shouldn't have to replace another one.

 

[shorebreeze]

For reference I had a cooling fan issue a year or two ago where the fan would only engage the highest power setting or off. The Sonic's cooling fan is a bit different from some imports because while, say, Honda takes the approach of having two side-by-side fans, and the power settings are very simply off-off, one off and one on (either way), and both on, GM has a single variable speed fan, and mine had gotten to the point where it would not run on the intermediate settings -- rather it would cycle between washing-machine-ultra-high-spin-speed and off. I guess there was some corrosion going on in the motor. In any case I had the radiator fan replaced. Sometimes this can happen due to blown relays but in my case the issue was apparently in the motor itself. The new fan is back to normal; it generally uses the low speed setting and never makes it up to the highest speed other than in very heavy stop-go traffic with a lot of air conditioning in extreme heat.

 

[Sonic636]

For reference I had a cooling fan issue a year or two ago where the fan would only engage the highest power setting or off. The Sonic's cooling fan is a bit different from some imports because while, say, Honda takes the approach of having two side-by-side fans, and the power settings are very simply off-off, one off and one on (either way), and both on, GM has a single variable speed fan, and mine had gotten to the point where it would not run on the intermediate settings -- rather it would cycle between washing-machine-ultra-high-spin-speed and off. I guess there was some corrosion going on in the motor. In any case I had the radiator fan replaced. Sometimes this can happen due to blown relays but in my case the issue was apparently in the motor itself. The new fan is back to normal; it generally uses the low speed setting and never makes it up to the highest speed other than in very heavy stop-go traffic with a lot of air conditioning in extreme heat.

How long does your low speed fan stay on for? Does it ever shut off or does it just continue to run on the low speed?