Another Fan Clutch Thread- Please Help Diagnose

[bdp1978]

Alright, before Roadie has to double up on his blood pressure meds...I have researched....and read....and googled. Ive spent 3hrs reading on the OS this morning and I'm still at a bit of a loss on my issue. SO, bear with me.

This started with a leaking water pump, I had no issues with the fan clutch prior to this.

I replaced my water pump and put everything back together, no leaks. I ended up with a wobble in my fan and the fan clutch roaring setting off a 526 code. I replaced the fan clutch, still roars, lost 2mpg, BUT, no codes.

I hooked up a 3rd fan clutch that was working perfectly that I pulled off my Dads truck. Same thing, roaring full time (Always engaged) but not setting off any codes. So, 3 fan clutches, all roaring, 2 with no codes.

Ive checked the #20 fuse, the 45 & 46 relays, all good. I'm going to replace my water pump again as the wobble should be attributed to a bad bearing in the pump. However, at this point I'm at a loss on the fan clutch, especially since it operated fine before I replaced the water pump and Im wondering why that would trigger the need for a pcm re-flash at the dealer???

Any ideas on this one??? Appreciate any help I can get.

[bdp1978]

I just posted it up on the OS, hopefully I get a hit. Mods feel free to delete if you want since Ive posted on both sites now.

[Trail X]

Brad, it's fine to post on both sites. We recommend posting a link between the two though, in order to reference any possible answers.

Does seem funny that all of the sudden you get a wobble once it's reinstalled, but not before. Seems something during your install could have caused the wobble, but I can't put my finger on it.

[The Roadie]

I'll probably reply there just so it gets indexed by Google, but I have a few questions. Do you have a meter? How could you determine the relay (solid state) was OK? Visual is not useful at all.

Pull the fan clutch fuse and the relay. Does it still overspeed?

[MrSmithsTB]

How long did you run the motor once the new clutches were installed? I ordered a new-ish clutch, and it required a good 15-30 minutes of run time before the roar disappeared. The fluid in a fan clutch is very thick, almost like silly putty when cold. When the clutch sits, the fluid settles. It can take quite a few minutes to get it moving again.

[bdp1978]

Bill, I've traced through with a meter, we've also pulled relays from my Dads TB which is functioning properly and still none of the 3 fan clutches work properly on my truck. About the only tool I don't have is a high level scanner. I just have a code reader. I've started this morning by putting in another new water pump and I'm just going to start over from scratch. I've ran both fans for several hours with no changes.

[bdp1978]

Another water pump fixed the wobble. Still testing on fan. Set off codes 2135, 2138, 641, and 526. So got the reduced engine power light due to the pcm signal. Everything is testing correctly but the fan is still staying engaged. The fun continues.

[bdp1978]

Bill, if you lose power to the fan does that trigger the fan to run fully engaged? Or does power on control it. I've got the 5 volts out of the pcm but my problem seems to be relating to the white wire somewhere around the hall sensor and cooling fan relay.

[The Roadie]

You need to do a couple of critical experiments.

Pull the fuse and relay to make sure NO power gets to the fan clutch. Run it that way for at least a half hour to warm up the silicone fluid that is the consistency of silly putty when cold. See if the fan roars under a no power condition. If it does, then suspect it's bad.

What did you trace with a meter? Power getting to the solid state relay? If the relay has power, you need to look at the FAN POWER (relay output) wire - a WHITE wire on Pin B of the fan harness. What is its voltage when the engine is cold? It should be very low. Check both DC and AC on the meter, because the signal is a PWM (a square wave whose low is ground and the high is 12V, but whose AVERAGE voltage varies according to what the PCM commands for fan RPM.)

Losing power to the fan should cause it to freewheel, and it will only spin near engine RPM by residual friction. You should be able to halt it with a rag.

The Hall Effect RPM sensor is the only part of the fan clutch to use 5V. If any of the fan clutches, or especially the short harness from the fan clutch to the engine compartment harness at the edge of the fan shroud, has a problem with 5V wiring insulation, that will interact with the APP and TBC sensor circuits and cause the REP behavior. But the fan clutch CONTROL only uses two wires, and the fan speed sensor is three wires, and they don't otherwise interact.

Another useful experiment would be to pull relay 45 and stick a constant 12V into the fan output pin 4 of the relay socket. I should have done this drawing YEARS ago to save time explaining the pinout of the relay. Sorry it took me so long.

[bdp1978]

Getting 12volts at the harness and 5. Even fully disconnected with no power to the fan we can't stop it. I just melted part of a rubber mallet trying to. Obviously this would lead me to believe both clutches I have are bad, but wouldn't explain why my Dads perfectly functioning one still won't work on my truck.

[The Roadie]

If you have 12V on pin 5 with the fan clutch disconnected, then there's a PCM failure or something in the wiring from the PCM to the fan clutch connector. If it stays locked up without the connector even plugged in, but the same unit works OK on the other vehicle, I can't explain that. Your ground may be bad - did you check that with your meter? - but I thought for sure it would freewheel without the connector plugged in.

Maybe I have it all backwards, and the fan clutch needs the relay to be ON to force it into freewheel mode. I'd have to go look at my truck to see if that's the way it's designed. The shop manual is not clear on which way the circuit is supposed to work.

NEW DATA! I looked in a DTC section of the shop manual, and I *DO* have it backwards. The relay is activated to command the clutch to go off. If you are seeing 12V on the control line AND the output to the fan clutch, then maybe it's not getting all the way to the fan? Or your ground could be bad. That would explain it all. See what voltage you have on the black wire on Pin A of the harness. That goes to ground point G103.

NOW: That totally conflicts with what has been posted by one or two owners who wanted extra cooling while towing, and added switches to force 12V onto the fan clutch connector to force the fan always on full speed. They claimed great effectiveness, and that can't be if it's a fail-safe design like this one. Everybody should go out and pull fuse 20 and see how their fans change behavior.

[Trail X]

I had disconnected my fan clutch connector and was able to stop the fan with a gloved hand before. Haven't done it in a while, but did it to show the possibility of stopping the fan for a deep river crossing.

[bdp1978]

Bill, thanks for your time helping me with this today. Been tracing electrical all day!! All voltages are correct but I'm not getting a steady 12v pulse like its supposed to. Used your 12v input into the 4 pin to diagnose. No voltage at the ground wire either. I have everything disconnected right now including the PCM. My goal is still to avoid a dealer visit.

[The Roadie]

The only other phrase from the shop manual that may help is that the clutch's reaction to the control voltage isn't instantaneous. It says it can take 1-2 minutes at 2000 RPM for the clutch to go to the commanded RPM. Still undecided is whether the fan is ON for 12V input or OFF.