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Radiator Fan Not Turning On

cyclonetron

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I’ve noticed my radiator fan is not turning on. I’ve checked all fuses and relays and they are good. I’m thinking it could be a bad thermostat temp sensor, bad radiator fan assembly, or something else.

Radiator fan won’t turn on when idle, driving, or when the ac is on.

Also, my ac isn’t working either but I’d rather just make sure my radiator fan works.

Engine temps stay no higher than 207 when driving and climb when sitting at a light.
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Check the following fuses in the BJB. Fuse 29-30amp; Fuse 31-40amp; Fuse 42-15amp; Fuse 55-25amp.
 
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cyclonetron

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Check the following fuses in the BJB. Fuse 29-30amp; Fuse 31-40amp; Fuse 42-15amp; Fuse 55-25amp.
So I’ve gone through and checked all fuses and relays with a voltmeter and they are reading fine. I also visually inspected the harness to make sure it wasn’t burnt out and the connections were good. At this point I’m going to manually test the radiator fan to see if it powers.
 

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Having the same problem. Except I put a bama tune on the car and they quit working. Returned it back to stock. Still no cooling fans. What was the issue?
 

Cobra Jet

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With car off - can you manually turn the fan blades? Is there resistance or do they spin freely when manually turning?

If the fan is inop, it could be seized motor bearings, bad connector, bad connection from connector to fan motor, or some other break within the fan harness wiring.

Have you let the car sit at idle for a long period of time to see if they would kick on?

Most electric fans usually kick on around 19*-210* depending on vehicle manufacturer sensor specifications and PCM coding.
 

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Is there a way to test the fans with FORScan? It'd be a lot easier, since our cars don't have a precise coolant temperature gauge (it's buffered, and stuck at the middle unless temp raises above 235F or so). If not, I think they should come on with A/C turned on, right? But it'd have to be above the temp threshold the compressor operates. Not sure what that is, but probably above 40F.
 

1miracle2

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Hello all.
So my fans aren't turning on. I've checked a few fuses mentioned prior by someone and they are fine. I decided to disconnect the fans power cable (on the back of each fan) and put a power tester to the terminales. Each terminal on each power cable has 2 prongs, when I touched each prong, all four had the steady beep. Shouldn't one be a ground on each fan or am I missing something?
Anyway, I was thinking to just order fans and replace them.
Can anyone confirm that each bung prong should have power?
Please and thank you 🙏🏾
 

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There are also 2 relays controlled by the PCM to test. In my experience it's usually a bad fan motor. Maybe this schematic and pinpoint test will help you diagnose the problem:
Fans.PNG
 

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1miracle2

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There are also 2 relays controlled by the PCM to test. In my experience it's usually a bad fan motor. Maybe this schematic and pinpoint test will help you diagnose the problem:
Thank you for the information. The pdf looks like i might be able to understand it for the most part but there are some things I don't understand in it.

I did some more testing.
I disconnected the terminal at the fan on the driver's side
Turned the car on
Turned AC on
Tested both terminals from the driver side plug and each had power
I then turned off the AC, left the car running and both terminals on the driver side no longer had power. My guess is definitely the fans are no longer functioning.
 

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1miracle2

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So I replaced the fans and they still don't turn on. I did test the old fans that I removed by providing power to them and the motors arent turning. Before installing the new fans I did provide power to them and they turned on fine.
After the new fan's wouldn't turn on while installed in the car I took them back off the car and tested the fans again to make sure they didnt get fried and they're still working.

So I found relay #77, #89, & #91 in battery junction box but I don't know how to test those. So ima look for a shop to just buy new ones.

Again my coolant tank originally cracked.
I replaced it. In the process I replaced the some silicone hoses and the thermostat to a 160° one ( it was used...🤔). Anyway, in changing that thermostat, I accidentally got some coolant on the alternator and it stopped working. I replaced it, power is fine now (wasn't charging old alternator after I spilled coolant but it is chargong the new alternator now). When I went for a test drive I noticed the cyl. head temp reached 250°ish. And that's how I found out the fans weren't turning. After replacing the fans I was letting the car get to 207° at idle and the fans still won't power up. I was turning on the AC and the defrost to try and trigger the fans but nothing.
I also noticed that if i turn the car on and turn on the AC, I get nice freezing air between 15-40 seconds and then it's just normal ambient/warmish air after that. I'm assuming it's because the second fan is for the condenser and it too isn't turning on but IDK.

I would really appreciate if someone can chime in and provide some help/suggestions.
I'm looking for part numbers for those relays. I tried using that .pdf testing but it's asking for some book to reference and i don't have it or know exactly where to get it.
All fuses are ok btw.
PLEASE & THANK YOU 😬🙏🏾
 
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spedy7

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2017_mustang_fans.PNG
2017_mustang_bjb.PNG


Here's both the proper wiring diagram for 2017's and the BJB (junction box in the engine bay). The diagram depicts the circuit at rest (before triggering either fan). If FC1 relay is triggered by the PCM, the fans will operate at low speed. If the PCM grounds FC2 and FC3, the fans will then operate at high speed.

I recommend getting a test light (normal incandescent bulb type, not LED), disconnect both fan connectors, and place the test light in place of the fan (don't damage the pins in the connector). If the light does not light up, check the power side of each to a different ground with the light and see if does light up. If it doesn't, could be bad ground or open in the ground circuit. If no power, I'd suspect fuses and then check relays.

If all 4 fuses are good, jump pins 1 and 2 at relays FC1 and FC3 with the test light (do not damage the pins) (to check for power to the relay coil and for PCM to properly ground the coil when requested). If it doesn't light up, again check pin 2 on each to a different ground to check for power. If there is no power and the fuses are good, suspect a wiring issue in/under the BJB (rare). If there is power, suspect a wiring issue to the PCM or a PCM fault. If you do have a tune, I recommend flashing back to stock. A coworker with his Fiesta ST had a tune on his and that tune alone caused the A/C trigger to not function until he reverted to a stock tune and then reflashed to his custom tune.

If the circuits are good, you can check the relays themselves by ohming out the coil side with a DVOM (volt meter). Usually pins 85 and 86 (most relays have a diagram on the shell), should be around 90-120 ohms depending on the relay design. If that is good, I would then suspect a wiring fault between the BJB and the fan connectors if there is no power to the fans still and ohm out from the BJB to the fan connectors. If the meter reads OL or more than 3-5 ohms, you have an open or high resistance in that circuit. Also best to ohm out C1074 to ground, should also be below 3-5 ohms.

Best of luck! Electrical can be pretty intimidating until you really understand it. I'm certain there are some sites out there that can assist with understanding automotive electrics in the general sense. I'm guessing a bad fuse, usually the case when fans "go bad" and pickup high resistance and passing the rated amperage for the fuse(s).
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