# Cooling fan



## Justin W (Apr 22, 2019)

Anyone have electrical diagram for cooling fan on a 2012 1.8L Cruze? It's a 3 speed fan controlled by 5 relays and there are 2 fuses in the circuit that I'm aware of.


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## ChevyGuy (Dec 13, 2014)

Sounds like the same thing the 1.4 has. Common failure is that the resistor pack that gives it the 3 speeds burns out, so until the situation escalates to "high" (aka "jet mode") the fan won't run.

Other issues can be sensor issues that cause the ECM to command high. 

But the relays themselves have been pretty good.


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## Justin W (Apr 22, 2019)

Ya mine is only running on low speed similar issue. I just want to see the circuit that's all. Already have a new fan ordered but I want to know how it's wired


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## plano-doug (Jul 1, 2015)

Here's one that I have. 5 relays? What were they thinking?!

HTH.

Doug

..


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## ChevyGuy (Dec 13, 2014)

Justin W said:


> Ya mine is only running on low speed similar issue.


Unless "slow" is all it can do when "high" is selected, that doesn't sound like a fan problem.

I'm having a hard time reading the electrical diagram. The one I've seen uses 5 relays to convert from "binary" to "one-of" (in computer speak).

That is, the computer has two output: A and B. A is "low", B is "medium" and A+B is "high". But the fan has three terminals: low, medium, high. The relays convert the logic as well as being a power relay.


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## Justin W (Apr 22, 2019)

No, mine works on low. When high is selected it does nothing. Thanks for the schematic Doug.

Justin


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## ChevyGuy (Dec 13, 2014)

Justin W said:


> No, mine works on low. When high is selected it does nothing. Thanks for the schematic Doug.


I don't think it's the fan. I'd suspect one of the relays. I think 3 are plug-ins in the underhood fuse box, but the other two are soldered in on the underside of the fuse box.


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## Justin W (Apr 22, 2019)

The relays have all be verified already. When it is calling for low speed the fan turns slowly. When calling for medium it won't turn unless I give it a push. Then on high it won't budge but there is voltage across the terminals to the fan. I suspect you are right that the fan motor isn't finished but it is one of the resistor packs you mentioned earlier. Since they are built into the fan assembly and cannot be changed then the fan assembly has to be replaced.... Was able to get one for $100 not too bad.

Justin


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## ChevyGuy (Dec 13, 2014)

Justin W said:


> The relays have all be verified already. When it is calling for low speed the fan turns slowly. When calling for medium it won't turn unless I give it a push. Then on high it won't budge but there is voltage across the terminals to the fan. I suspect you are right that the fan motor isn't finished but it is one of the resistor packs you mentioned earlier. Since they are built into the fan assembly and cannot be changed then the fan assembly has to be replaced.... Was able to get one for $100 not too bad.


That's weird. "high" bypasses all resistors and applies power straight to the fan motor. If it was a bad motor, I'd expect it to limp on high and not function at lower settings - not the other way around.

But it just goes to prove things can fail in strange ways. I wonder if that fan was a aftermarket replacement. Non-OEM parts can fail "differently".


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## Justin W (Apr 22, 2019)

Ya. Not sure but I'll post the outcome once the new one is installed. There are actually 3 terminals plus a ground at the fan connector. From what I've read the resistor bank is built into the fan assembly past this connector.

Justin


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## ChevyGuy (Dec 13, 2014)

Justin W said:


> From what I've read the resistor bank is built into the fan assembly past this connector.


Indeed. It looks replaceable, but it's hard-wired in and sold as part of the fan. 

I've often wondered if it's the resistors that fail, or a dying fan motor that draws too much current and burns out the resistors. So, there may be something said for replacing them together.


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## Justin W (Apr 22, 2019)

Yes I tend to agree with you. If I were very ambitious I'd probably try to find out the resistance for each speed and just wire it myself with resistors. But I don't have that kind of time on my hands unfortunately. The fan does spin but I swear it sounds like the motor bearings are on the way out so that could easily be the cause of resistor banks failing.

Justin


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## Justin W (Apr 22, 2019)

Completely forgot to post the outcome on this. I replaced the fan and it works great now on all speeds. After topping up the coolant from the loss through the overflow when the fan wasn't working I also had to replace the o-ring on the overflow cap as it was leaking by when the engine was warm. Running great now 172,000 Km hopefully many more.

Justin


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## Blasirl (Mar 31, 2015)

If by any chance you still have the old fan, can you ohm it out just for grins. It is always nice to have a god/bad number handy.


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## plano-doug (Jul 1, 2015)

On the subject of cooling fans and the drawing attached in post#4 above, I did some analysis, mainly to try to understand why it takes 5 relays to control 3 fans. The table below summarizes the results. The two columns on the left show the two control signals from the ECM. The 5 relays are highlighted in blue. The fan speed is shown on the right (Airflow).

Ultimately, the outputs of three relays drive the three inputs to the fan. CFM2 is at +12V on low. CFM3 is at +12V on medium. And CFM4 is at +12V on high, in which case CFM3 and CMF2 are also at +12V.










My best guess as to why there are 5 relays is that maybe the two extra relays, KR20F and KR20E, provide some measure of fail-safe for the system, to ensure that the fan still operates, albeit at a different speed, even if one of the 3 speed controls relays (KR20D, KR20P and KR20C) is malfunctioning. But I'm not sure I can prove that 

Anyway, if someone wants to know how the 3 fan settings are derived from the two ECM pins, here's a summary. A pdf version of the table, and another version of the schematic, from a different source, are also attached.

Doug

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## ChevyGuy (Dec 13, 2014)

Your chart doesn't agree with that I'm seeing in my 2013 manual. 

But to answer why 5 relays - 3 large relays are used to send power to one of three terminals that control the fan speed (resistor pack). The other 2 relays are used to decode the 2 outputs of the ECM into 3 speeds + off. Not sure why GM felt they had to save a pin on the ECM. Fortunately, this kluge seems to rarely be a problem. It's usually the resistor pack.


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## plano-doug (Jul 1, 2015)

ChevyGuy said:


> Your chart doesn't agree with that I'm seeing in my 2013 manual.
> 
> But to answer why 5 relays - 3 large relays are used to send power to one of three terminals that control the fan speed (resistor pack). The other 2 relays are used to decode the 2 outputs of the ECM into 3 speeds + off. Not sure why GM felt they had to save a pin on the ECM. Fortunately, this kluge seems to rarely be a problem. It's usually the resistor pack.


I'd be curious to see what's in your manual - I could have missed something. I had the same thought about using a 3rd ECM pin. I don't want to pick on GM - they have some pretty sharp folks there - but it does seem kluged 

FWIW, on the w-bodies, the ECM has 2 outputs controlling 3 relays which in turn control 2 fans that supply 3 levels of airflow (+ off). That is, they achieved essentially the same thing with 2 less relays.
...
On a different note, comparing the schematic and the labels inside the fuse box, there's a huge disconnect in the reference designators. So it's not clear which relay does what. I'll figure it out eventually, but I was a bit amused that two different sets of labels were used 

Doug










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## Priscilla (Mar 9, 2021)

Justin W said:


> Completely forgot to post the outcome on this. I replaced the fan and it works great now on all speeds. After topping up the coolant from the loss through the overflow when the fan wasn't working I also had to replace the o-ring on the overflow cap as it was leaking by when the engine was warm. Running great now 172,000 Km hopefully many more.
> 
> Justin


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