High Speed Fan Issues

[Houdinii_5.0]

Has anyone had experience with code P0481? I have a 2015 GT tuned by Lund. The fans come on as soon as I start the car but I don’t think the high speed setting is working. They just stay on low all the time which I think has contributed to my high CHT when in stop and go traffic. I’ve tested the fuses and they all seem fine. No connections are melted and everything looks normal on the fan. Any ideas? I’m about at the point of just replacing the fan assembly.

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[ORRadtech]

Have you connected to a bidirectional scan tool? They often allow you to activate different components to test them. Other troubleshooting options would be a DVOM or a small, handheld oscilloscope to tell if the fan is getting a signal.
In short, there are lots of things you can try before loading the parts cannon.

 

[G.T.]

Maybe check the 3 fan relays in the fuse box.

Someone here kindly explained how the system works and symptoms of failure of each relay and IIRC that was one of them.

EDIT - I just swapped relays around to test, 2 of the fan relays are 5-pin and one is a 6-pin. Lots of same relays in the fuse box.

 

[Skye]

Issues/Concerns:

1. Fans coming on immediately at car start. They should not, unless the A/C is on (See Dallas. ).

2. If temps are approaching 223F, the fans should then engage at high-speed, 100%. They aren't.





I'm attaching some diagrams that help define the logic and map the layout in a stock setup.

If CHT is below 212F / 100C and the A/C is turned off, the fans should be off.

If the CHT reaches 212F / 100C or the A/C is turned on, both fans will engage in series. 40% power.

If the CHT continues to climb to 223F / 106C, both fans will engage in parallel. 100% power.

That both fans are working, IMO, that clears the fans themselves.

When did this issue start? Can you correlate that to anything involving the Lund tune?

Before considering the replacement of parts, I'd discuss and confirm with Lund the tune's fan logic.

If Lund's programming seems correct, maybe start by checking/replacing the fan relays.

 

[Houdinii_5.0]

Issues/Concerns:

1. Fans coming on immediately at car start. They should not, unless the A/C is on (See Dallas. ).

2. If temps are approaching 223F, the fans should then engage at high-speed, 100%. They aren't.





I'm attaching some diagrams that help define the logic and map the layout in a stock setup.

If CHT is below 212F / 100C and the A/C is turned off, the fans should be off.

If the CHT reaches 212F / 100C or the A/C is turned on, both fans will engage in series. 40% power.

If the CHT continues to climb to 223F / 106C, both fans will engage in parallel. 100% power.

That both fans are working, IMO, that clears the fans themselves.

When did this issue start? Can you correlate that to anything involving the Lund tune?

Before considering the replacement of parts, I'd discuss and confirm with Lund the tune's fan logic.

If Lund's programming seems correct, maybe start by checking/replacing the fan relays.

Thanks for the diagram. The code has shown up since I purchased the car in January. The car had other issues at the time that I was addressing so I didn't think much of it. I didn't really notice the affects until summertime rolled around. From my understanding Lund does trigger the fans to come on earlier than the stock calibration. My CHT will get up to 230-235 though and the fans aren't blowing any harder than they do at lower temps.

When I run Forscan it shows a fault for High speed fans. I have already put a new relay in the FC1 position, but nothing changed. Correct me if I'm wrong but it looks like off the diagrams FC2 would be the main culprit? Every relay reads 80 ohms with my multimeter. The relays are fairly cheap though so I might just buy 2 more to replace FC2 and FC3.

 

[Houdinii_5.0]

Maybe check the 3 fan relays in the fuse box.

Someone here kindly explained how the system works and symptoms of failure of each relay and IIRC that was one of them.

EDIT - I just swapped relays around to test, 2 of the fan relays are 5-pin and one is a 6-pin. Lots of same relays in the fuse box.

When I pulled the relays FC1 and FC3 were 4 pin. FC2 is 5 pin. I found another post where a guy talked about diagnosing by starting the car and pulling FC1. He said if the fans stopped when FC1 was pulled then it meant that relay was bad. Mine did stop when I pulled that relay but when I replaced it with another relay it didn't change anything. I would think pulling FC1 would cause the fans to stop no matter what so I'm not sure that's reliable for diagnosing.

 

[Skye]

If Lund is programing them to come on sooner, that could be OK. But I wonder how their programming affects high-speed fan ops.

In the table above, notice the "40" and the "100" setting involving the Engine Coolant Temperature. If someone was cut-and-pasting 40s all through, that could stick them at 40%.

Looking at the diagram, this is my understanding of the relays:

FC1 fails:

- If A/C is turned on, or, if CHT reaches 212F, neither fan will turn on

Both fans are running at low-speed. I consider relay 1 good.

FC2 fails:

- At rest, relay 2 completes the interconnection supporting fans 1 and 2.

Both fans are running at low-speed, so that branch of relay 2 is good.

- Engaged, relay 2 terminates fan one at ground, so it can run at 100% speed.

That's not happening. That portion of relay 2 could be bad.

FC3 fails:

- At rest, relay 3 completes the interconnection supporting fans 1 and 2.

Both fans are running at low-speed, so that branch of relay 3 is good.

- Engaged, relays 3 supplies power in parallel to fan 2, so it can run at 100% speed.

That's not happening. That portion of relay 3 could be bad.

You could reach out to Lund. Explain yourself. Ask them to do a top-down review of the existing tune. Just troll it for anything that might be unique or unusual. While that is going on, replace FC2 and FC3.

I googled for similar examples occurring before in 6G threads. There was one of the 0481 code. In this example, neither fan or the A/C were coming on. The OP suspected the battery might be at fault. They didn't come back and update the thread. They were last seen in 2023.

https://www.mustang6g.com/forums/threads/old-battery-causing-voltage-issues.174463/

 

[Skye]

I would think pulling FC1 would cause the fans to stop

Yes. Pulling FC1 would break the circuit for 40% operation. Neither fan would work. Pulling FC1 would at least disable Fan 1 during 100% operation. I assume if FC3 was good, fan 2 would spin at 100%. Seems like a good idea. If that portion of the circuitry fails, fan 2 would still engage at the higher temps, when most needed. My thoughts though. I've never tested that.

Correct me if I'm wrong but it looks like off the diagrams FC2 would be the main culprit?

It's my belief FC2 and FC3 are both needed for both fans to run at 100%. See my comments above.

As you mentioned, they're simple enough to replace. It'd remove any doubt in future discussions with Lund or others.

 

[G.T.]

When I pulled the relays FC1 and FC3 were 4 pin. FC2 is 5 pin. I found another post where a guy talked about diagnosing by starting the car and pulling FC1. He said if the fans stopped when FC1 was pulled then it meant that relay was bad. Mine did stop when I pulled that relay but when I replaced it with another relay it didn't change anything. I would think pulling FC1 would cause the fans to stop no matter what so I'm not sure that's reliable for diagnosing.

Yes you are correct, I misremebered and added a pin each lol.

I am actually in the process of replacing all the relays myself. They seem to like to stick. Horn, defroster, and wiper have been acting up and swapping relays have gotten them working. I noticed the newer relays have a different part number and hopefully improved.

Skye has it covered on fan operation and troubleshooting with regards to the relays, hope it's something simple in your case.

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