Now that it's spring and I want to drive the car I have revisited the fan not working issue. The original post appears here:
https://www.corvetteforum.com/forums...coming-on.html

I went to the Dealership and after I got there the fan was working fine. They said everything was operating normally. Which it does when the fan works. Part of the problem is that the condition is intermittent, although it does not work most of the time.

The Service Manager says that the most likely problem is that the programming for the fan curve, installed by ECS when they installed the SC is wonkey. Is that even possible, I mean it either doesn't work or it works fine.... He further states they will not work on the car again unless I have the ECM reflashed by ECS, including the fan curve.

He further states that the only time they have fan problems is when there have been modifications.

One thing I have not checked, when the fan is not working, is shorting the temp sensor to see if that turns on the fan. Are there two sensors, and if so which one is the one that needs to be shorted. I read that one sensor provides signal to the DIC and gauge and that the other sends signal to the ECM. Is that accurate?

What are the chances that I need to replace the ECM? Something I don't want to do only to find out that it's not the problem.

I'm at my f'ing wit's end here...

 

I think your dealship is full of ****, and, as is typical of dealerships and politicians, instead of actually trying to diagnose what's wrong, they immediately set out to find someone else to blame. An intermittent electrical problem like that is usually a symptom of a bad connection/ground or a faulty sensor. The only how that I could see that it could be the tune is if somehow someone zeroed out the fan power percentage tables at a certain point, in which case it would always happen at a certain temperature range. That would be easy to spot from anyone taking a look at your tune.
I would try to chase the wires and see if anything is getting pinched or if a wire is broken inside the insulation or something like that, before I buy a new ECU, in which case you would have to get that flashed with your VIN and OS and have the ECS tune reloaded.
Maybe just try to find a competent shop and have them have a go at it. Dealerships generally suck *** at anything other than selling you parts imho, and even that they're not so great at.

 

First thing is to check the ground on the harness connection near the fan, from there I would have to take a look at it. One thing for sure though, I cannot tune the fan to be intermittent.

There is only one temp sensor on the left front head, but you should have the car put on a scanner and manually operate the fans from that to check their functionality.

ECM's rarely ever fail, I have seen it, but it's very rare. I have seen a program glitch cause what you are seeing, but that is also very rare though. All I had to do was hand write the file over again and download. If you compared the two files it showed as "0.00 difference between files", yet it fixed it.

Let me know if you would like me to take a look, I'll be glad too.

 

^^^^^^That's World-class customer support right there!

 

100%

 

Thank you Doug, you guys have been nothing but the very best with me regarding some minor fixes along the way and plenty of "stupid" questions.

The confounding aspect of this is that when it works, everything is normal. When it does not, the DIC and the analog gauge indicate the proper temperatures...so doesn't that tell us that the appropriate signal is also being sent to the ECM? But then the ECM is not sending the pulsed ground signal to the Fan Control Module. I assume the Pulse Width Modulated signal is, in effect, an intermittent ground. Which is why I can make it work by doing what I describe in the paragraph below.

When the fan is not working, I can make it work by grounding the signal wire from the ECM to the frame...simulating the Pulse Width Modulated signal from the ECM. So doesn't that tell us there is not a problem with the ground wires on the upper frame, and also, again, no signal from the ECM? And I have previously taken those ground wires off and cleaned them.

I can also make the fan run by jumping the connector at the Fan Module.

I'm no expert, but it appears to me that the ECM is receiving temperature information but not telling the fan to run.

I can bring the car down there, but it is a four hour drive...with no fan. Unless I wire a switch to run the fan at 100% when needed. At speed, the temp is ~230 and most of the trip is Thruway/NJTP. Or, if it can be driven on to a U-Haul trailer I could do that. I've got a Silverado 2500... If you think I should, I will.... I'll even buy a box of doughnuts.

Thanks Doug...World Class Service...

Gary

 

Let me ask this: does the Pulse Width Modulated signal provide ground or positive through the wire from the ECM to the Fan Control Module?

 

Got your PM. I'll reply here, as it might help others as well.

The ECM pulls the PWM wire to ground/open intermittently, just as you're doing when you're shorting the PWM wire to ground.

Since shorting the PWM wire to ground makes your fan run, your connector is most likely not melted, and the fan controller is most likely good. It's most likely a broken signal wire between the ECM and the fan control module. I had the same issue, and the only way I could fix it was to run a new wire from the ECM directly to the PWM input of the fan control module. See my previous post in another thread https://www.corvetteforum.com/forums...ling-fan.html:

"The problem in my case was that the PWM signal was interrupted somewhere along the way, so the controller never got a signal from the ECU, and my fan would never turn on. So I ran my own wire directly from the ecu terminal to the pwm controller, bypassing the car's wiring. You will have to look up in the schematics which ECU pin to tap into."

In your PM you asked:

"Couldn't the fan be hot wired by running a switch between the PWM wire to the controller and ground? Wouldn't that be safer?"

Yes, if you wanna sit there and flick the switch on and off every 0.5 seconds

The fan doesn't run with a constant ground signal. Try shorting the PWM wire of the controller to ground for a long time. The fan will turn on and then turn off. According to my testing, the controller expects a pulse width modulated signal with <90% duty cycle in order to run the fan, not a constant ground.

If you want to check whether the ECM is giving a PWM signal, hook a voltmeter or light bulb between the PWM wire and 12V. Or an ohm meter between the PWM wire and ground. Or a duty cycle meter between PWM and 12V. If you get no signal on the wire (it's always an open circuit), even when the engine temp sensor is disconnected, then you know you need to look for the signal getting lost further upstream.

The next step is to tap into the wire at the ECM harness under the passenger side fender. I hope you have access to the schematics to find the correct wire. Hotwire it directly to the PWM input of the controller. If the fan still doesn't come on, check the PWM signal at the ECM.

If there is no PWM signal to ground at the ECM, then the ECM is either broken, programmed wrong, or the temp sensor wiring is shorted.

Good luck!

Steve

 

Thanks for the reply. I was afraid of that.... I'm currently sourcing the appropriate relay to wire in a manual switch. Is this 50A NO suitable? I've had a test light wired in to the signal wire since the day the Service Manager told me not to come back...when five minutes later the fans stopped working, again, and haven't worked since. Go figure.

Are you saying that if I simply disconnect the temperature sensor, that should trigger the fan? I had read in other posts to disconnect the sensor and short between the terminals. I could use some clarification on that.

At this point I'm convinced the problem is no signal from the ECM...for whatever reason. If I could get information on what pin in the ECM the signal wire originates, I could test to see if it's the wire, but I don't have access to that information. Once I have the switch in place I could take Doug up on his generous offer.

Anybody have that ECM schematic/wiring diagram and would like to share with the rest of the class...?

2011 GS

 

Sorry for the late reply.

I've seen people mention just unplugging the temp sensor to get the fan to turn on. If that doesn't do it, try shorting it.

The relay should work, but don't bother with it. Most likely all you need is to run a wire from the ECM to the fan control module.

I dug up the schematics for you in the service manual. What you want is ECM connector X1, Pin 58, color D-GN (dark green, I think). Remove fender liner from front passenger fender to get to it. It's at the bottom rear of the fender well.

I think the picture of the connector shows the ECM side, not the harness side (though I could be wrong). Use the list of wire colors around 58 for context, to make sure you have the right wire.

PS: I highly recommend buying a digital service manual. The one I have is a pirated copy on CD from ten years ago. That reminds me: my manual only goes to 2009. I doubt they changed the wire colors, but FYI...

 

Thanks, you have been a great help. This is just what I need. I can now test for continuity on the signal wire and, just to be thorough, test for signal off the ECM with the temp high. I'll check to see if the sending unit does anything, but I doubt that will change anything. I don't think there is signal from the ECM or, perhaps, a bad signal wire to the fan module.

In the mean time, I ordered the Casper's switch. I figured if I use it I'll stay at 90% max and minimize my potential to burn up anything in that circuit. Although it's probably only a matter of time. I've been lucky so far and have not had that issue.

I'll post my findings when I have them, maybe someone else can benefit from my experience.

Thanks again,

G