PowerLabs

I'm at my wit's end on this one... Here is the story:
My cooling fan stopped working during a long high speed run last year. Right as the car hit the 200MPH peg on the speedo the DIC said said "Service Charging System", the voltage dropped to 12V (I.E. The alternator protection kicked in and the car started running off the battery), and it basically ran its battery down. I replaced the battery, the alternator was fine, but the fan never worked again (it stopped working during the run).
Here is what is NOT wrong with it:
- ALL THE FAN PLUGS LOOK PERFECTLY FINE (yes, I know this is a common issue. That is not the problem here, they are not corroded, or molten, or anything. Yes I checked both of them.)
- THE FAN WORKS
- THE FAN FUSE IS FINE
- THERE IS POWER AT THE FAN CONTROL MODULE

I found that I could run the fan by jumping the wires on the control module, so I assumed the module was bad and replaced it. With the new module I still couldn't tell the fan to turn on via HP Tuners (does that work for anyone?). But I found that once the car hit 196F it would turn on by itself.
For 6 days. Yesterday as I was driving home the fan stopped turning on. And let me tell you; in traffic, the car will overheat AMAZINGLY fast when that happens! I basically have 20 seconds to get moving again to force air through the radiator before I have to pull over and shut it down to prevent damage. This is frustrating beyond words!

Looking at the PIDs on HP Tuners, I can see that even with coolant temps in the 230F range the FAN %, FAN Desired % and FAN Desired RPM are all 0. I can tell the fan to turn "ON" as well, and nothing happens. But that was also the case before, and it still worked anyways, so I can't say for sure that what I am seeing on HP tuners is accurate.
I can pull the plug on the fan speed controller PWM module), jump the ground and power pins, and turn the fan on at full speed. This tells me that the fan works, the plug is fine, the fuse isn't blown and there is power available. The problem can only be the following:
1- The PWM module is bad. Possible, but this is a brand new module.
2- The ECU is not telling the fan to turn on (supported by what I see on HP Tuners). But WHY?? I have NOT changed the fan settings on HP tuners; it went from working to not working during a drive for no reason whatsoever. If this was a hardware issue I would expect to see the commanded fan speed show up as something other than zero on HP tuners, unless that PID does not work.

A new fan speed controller costs around 300 bucks. That is very close to the price of two fan upgrade for my DeWitts radiator, but I would feel like an IDIOT ripping off a computer controlled PWM fan and jerry rigging a thermostat in there just because I couldn't fix it. Not to mention this is a DD and those fans are noisy.

Still, I am running out of options. Do I buy ANOTHER speed controller and hope it works? Is the ECU the problem? Any ideas?

Thanks. If you can figure this one out you are smarter than I am

REVAK

Well like you said, you know what it isn't. From what you've told us, I would be suspect of the fan percentages bring absent. It's not likely you have 2 bad fan modules. I am not a computer guy, [retired mechanic] , Have you tried to reprogram your desired fan percentages ? If so , and they don't appear on a read, I would suspect the ECU. If you are seeing proper temperature sender readings, and you know the fan runs, seems like the fan module is not being commanded on by the ECU. I think the ECU sends a square wave signal to the fan module , if you have access to a scope you could monitor that wire into the fan module to verify. No signal, the fan can not run. I think a TECH2 can read and simulate that signal. That may be the most expedient path to a solution. In the mean time, I would run a manual over ride switch with a ballast resistor, around .75 to 1 ohm for an approximate 60% fan speed to protect your engine. [ approx. 100 ft. of 14 gauge thhn stranded wire , coiled up, will give you that resistance] Good luck.

knkali

seems like ECM given all the things you have checked. Maybe the high speed run/power surge freaked out the ecm? If you wanted, Spal makes a stand alone controller if that would save you some $$ not going with a new ECM.

carlrx7

i would suggest that you REWRITE over the fan tables.

open your tune,

open compare stock tune file

reset all your fan settings to stock,

now flash your car.

turn off car, wait 30 secs. then start,

see if that worked? if so, retune your fav vs coolant temp table to 25, 50, 75, 99 --->

if no worky, then try changing ALL the values on the System>Fans tabs to something differnt, Flash, then bring it back all to stock then flash again,,

other than that is just get a new pcm, i think there 150 bucks,, but i think you'll have to re license you pcm, $$$

hope something helps.

-Carl

HOXXOH

Not being a computer/electronics guy, I may be way off the mark here. Is there only one temp sending unit or could there be two and the one that senses for the fan control has gone south during that run where you had other electrical issues.

TwinSpin

Why not replace the control box with a simple relay?

knkali

this would be simple and cheap

PowerLabs

What a great idea! Maybe I can replace my PCM, fuel injectors, fuel rails, crank position sensor, etc etc with a simple carburattor too while I'm at it?

chaver450

i think i may be having some fan troubles also. at what coolant temp should the fan kick on?

drivinfast

This must be very frustrating Sam....when my harness connector fried in 100 degree heat in Houston, I had a 70mph freeway drive back to the house and the temp stayed at just under 200...of course mine was an easy fix of bypassing the burnt harness...

you cant take your car anywhere for fear of the overheating which can happen in a few seconds in bumper to bumper.

I've had C6 owners tell me the weirdest things. guy was getting a MAF code(sorry dont remember it) and Cen21 and others could not figure it out. so he gets to digging around and traces the harness from the MAF and about a foot into it he comes upon a sort of out of place set of connections. so he redoes those and no code so far....I will have to check it....

I cant help but think that during the reinstall something got pinched or something and is the issue...

Zteve

I would also recommend you wire in a simple manual override switch so you can turn the fans on from inside the car any time you want regardless of what the computer is telling the fans to do.

carlrx7

PL,

see if you can't get one of your tuners to throw in a dummy PCM, and check it, if they wont do it, send me your current tune file, ill do a compare and put all your values in my PCM, then ill ship you my PCM. im going to iraq for a week, so dont need the car. can ship out pcm on monday if you want. but you gotta get it back to me by th 10th

-Carl

or you can send me yours, doesn't matter

HOXXOH

Hey, we know you're frustrated, but I'm sure he meant well.

If the fan motor works, that would solve your immediate problem and give you time to find the root cause.

I'm sure you remembered to turn on the heater full blast and pop the hood latch just to get home.

PowerLabs

I have a switch on it so I can continue tuning the car and driving it. That is a "hack". I was hoping to get help finding a fix here though; I don't need help doing a hack...

vetehead

Just a thought here....I'm sure you probably checked this already but you don't list it.If you have the service manual locate the circuit that sends the signal from the ecu to the fan control module and test that wire for continuity, intermittent opens and ground.The next step would be if wire checks out , then make sure the said wire is not shorted to any other wires in that harness.The last test will be time consuming because you will have disconnect the devices on the other end IE sensors relays etc....If the wire or wires from the ecu to the fan control module check out,I would say a bad ecu driver output on that circuit....assuming the tune is correct that is(I'm sure you have triple checked that).Hope this helps

Ron

HOXXOH

The nearly 200 people who have visited this thread with the intent of helping you didn't know you already had a temporary fix in place, as you failed to mention it before.

A little civility toward the people who are trying to help you, will go a long ways now and in the future.

Tony B4

Just a suggestion, set fan at 40%@192, and 90% for every value after 192 degrees. I would do this on a "write calibration only", not a rewrite entire.

Wondering if someone tuned your car with something other than HPTuners? I could be wrong, but if so, you may not see what they did with different tuning software with your HPTuners, and that could be your problem.


Tony B.

k0bun

You're wasting your time.

PowerLabs

I tuned the car this time using HPTuners. The fan was running perfectly fine, then it stopped during a highway drive out of the blue:
This did not coincide in any way with a tune or a reflash so it can't have been caused by it. Also my fan table has been the same since over 32,000 miles ago, I never touched it, and it never gave me any problems until now...

I am going to use a Tec2 to flash a stock tune into it and see if the Tec 2 can command the fan to turn on... Tomorrow. I have a feeling it won't.

Motorhead-47

Any value over 25% in the 192 field will cause the fans to run 100% all of the time