Engine Fans Always On
 

Every time I start the car, the cooling fans kick on after about 5 seconds.

I originally had an issue with the AC pressure switch. I fixed that, but the fans still continue to run.

Is there a sensor that can go bad? Maybe a fuse? I only have a basic scan tool, and the only codes were for the EVAP which I believe I fixed with a new purge valve.

Thanks for any help.

There's a 30a fuse and a relay on the right side. The fuse wouldn't be the issue, but you can replace the relay for a couple bucks and see if that resolves the issue.

Years ago I had a relay that got stuck open and my a/c didn't work. I wonder if the fan relay is having this issue now.

Thanks.

Each fan is controlled by separate relay. I'd doubt you have 2 stuck relays. I'd bet the ECU is still commanding the fans on for some reason. I know you said you fixed the AC pressure switch but even with it working, if it reads a certain system pressure it kicks on. Idk if you disconnected the sensors altogether if it would default on or off but may be something to try real quick. If your fans don't come on in 5 seconds with pressure sensors disconnected you'd know that's what's causing it.

Yeah, I moved the relays around and no change.

Also I'm pretty sure they come on even with the pressure switch disconnected.

Also I should note, the temp readout still works, so I don't think it's the t-stat or coolant temp sensor.

If you haven't seen your temp gauge spiking either, check the connections and see if there's corrosion.

Nope, normal temps.

The only other thing I can think of is I used the AC pressure switch for a wideband back in the day. Not sure why it'd start acting up now though. I checked the wiring and it looked fine.

I noticed if I key the ignition on but don't start the car, the coolant temp read -40*F.

When I started the motor the temp read normal.

No codes, fan still at full blast though. Can't figure this one out.

How much would it be to purchase a new one just to pop it in and see if it's sending bad signals to the computer?

I don't think it's the sensor because even when it reads properly the fans are on full blast.

Is there some kind of sensor that I might be missing? Is there one on the fan itself?

It's weird because I'll drive and my coolant temps are normal by the time I get to where I'm going. I just feel like I'm going to wear the fans out with them on all the time. Although I'm sure the intercooler is happy.

Mine used to run all the time and I didn't worry about it. Think biggest tax is probably drag on alternator and fan wear which will reduce gas mileage but replacement fans are actually relatively cheap.

I'm thinking it has something to do with AC pressure, but it shouldn't do it with the AC off. My compressor still kicks on with defrost, etc.

Mine was because of the AC system pressure. Didn't matter if AC was on or off. AC worked normally. I just know it didn't do it when my AC system wasn't charged but after I charged it the fan ran all of the time.

At least the IAT2s will be lower at idle lol

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Following.....mine dont turn off either

Strange!

I feel like they are only on when the car is stopped or at very low speeds, because if they were on while driving my coolant would never make it to normal temp. At least that's my theory.

Fans are indeed cheap, so I probably will just leave it. It'll definitely help with IAT temps while stopped.

Your thermostat prevents fluid from flowing through the radiator unless your coolant is 180 or 185 (don't specifically recall) so your fan doesn't significantly effect coolant temp until your thermostat opens.

good call

You can hear the fans kick on ~ five seconds after the car starts.

Have you tried just disconnecting the electrical connector from the high-side AC pressure switch? I'd think that should stop the fans from coming on if it is because of high AC system pressure. I stole this from another thread.


For the LSJ:

The PCM commands Low Speed Fans ON under the following conditions:

• Engine coolant temperature (ECT) exceeds approximately 106°C (223°F).

• A/C refrigerant pressure exceeds 1 310 kPa (190 psi).

• After the vehicle is shut off, the ECT at key-off is greater than 140°C (284°F) and system voltage is more than 12 volts. The fans will stay on for approximately 3 minutes.

The PCM commands High Speed Fans ON under the following conditions:

• ECT reaches 110°C (230°F).

• A/C refrigerant pressure exceeds 1 655 kPa (240 psi).

• When certain DTCs set

When the request for fan activation is withdrawn, the fan may not turn OFF until the ignition switch is moved to the OFF position or the vehicle speed exceeds approximately 10 mph. This is to prevent a fan from cycling ON and OFF excessively at idle.



For the LNF:

The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated (PWM) signal to the cooling fan control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the PWM signal. The cooling fan speed can be adjusted from 10 percent to 94 percent duty cycle. 94 percent is considered high speed fan.

The ECM commands fans ON under the following conditions:

Fan Control During Engine Operation (Engine ON)
• Fixed 94 percent duty cycle commanded when the following conditions are met:

- Engine oil temperature is greater than 140°C (284°F).

- AT transmission temperature is greater than 140°C (284°F).

- Intake air temperature is greater than 65°C (149°F).

- Engine coolant temperature sensor faults have been detected (electrical or rational).

• Variable duty cycle from 15-95 percent is commanded when:

- From all available requests, the maximum requested duty cycle is selected and commanded.

- Dependant on engine coolant temperature, 0 percent up to 92.9°C (199.22°F). Then 15 percent at 93°C (199.4°F) to greater than 94 percent by 121°C (249.8°F).

- Dependant on A/C pressure sensor, 0 percent up to 10,979 hPa. Then 15 percent at 10,980 hPa to greater than 94 percent by 23,529 hPa.

- Fans commanded off during running operation when the above conditions are not met.

Fan Control During After-run (Engine OFF)
• Fixed 36 percent duty cycle commanded after shut-down when the engine coolant temperature at shut-down is greater 101°C (213°F).

• Fixed 60 percent duty cycle commanded after shut-down when the engine coolant temperature at shut-down is greater than 108°C (226.4°F).

• Fans commanded OFF during after-run when:

- System voltage is less than 11.5 V.

- After-run time is greater than 420 seconds.

- Coolant temperature drops below a variable threshold

Isn't the high and low pressure switch the same thing? If so I disconnected that already and the fans were still on full blast.

I haven't ever messed with the AC system sensors on my Cobalt but typically there is a low-side and high-side switch or sensor that have to be separate because they measure the pressure on either side of the compressor. High-side sensor measures for if the pressure exceeds a certain threshold on the compressor output and low-side sensor measures for pressure dropss below a set threshold on the intake side of the compressor. From the text I pasted above it looks like the Cobalt sensor actually reads pressure. Older AC systems would just have a pressure switch on both sides that would break the circuit to the compressor if either the high side was too high or the low side too low.