My fan stopped working last fall and I figured it was just the PWM fan speed controller... Replaced it with a brand new factory one, but the fan still doesn't work. I can turn it on by jumping the fan wires, so I know the fan is OK, I know the plugs are fine and I have no reason to believe the wiring could be damaged... Could it really be the ECU?

Does anyone have any suggestions on how I can go about testing if the ECU is sending out a signal for the fan to turn on? More specifically; does anyone know what the fan "ON" signal looks like? I'm guessing it is probably +5V coming through the thinner red wire on the plug, but is it a variable voltage or a square wave?

 

Those fans should be hot wired, meaning you have power to the fan's at all times, most of those fans work buy a signal switch that creates a ground.

Probe the wires useing a test light when you touch the right wire creating a ground the fans will start, this is the same thing the computer does, if you can't find the problem you can create an overide useing that wire and a switch to ground, untill you can figure out the problem.

 

I already did that:


That's what I was doing before, but now I've got the car inside and I am trying to fix it.

 

There is mechanization in HP Tuners that allows you to control the fan speed real-time from the laptop. Perhaps that would help you?

 

That is how I test it; I command the fan to turn on, and it doesn't. I then check that the fan works by jumping the plug to power it directly; it works. The problem then has to be with the pulse width modulator (which is brand new) or the ECU...

 

What are you using to "command the fan to turn on"?

 

hmmm. ecus are pretty cheap, but then you have to relicense the new ecm, which cost almost the same as a new ecu, just to see if fixes it. .

go post on the hptuners forum, i wana say i saw something about having to do a full flash, but i might be wrong, have you done any 2bar upgrades recently?

-carl

 

Cooling Fan Inoperative

Circuit/System Description

The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated signal to the cooling fan speed control module. The cooling fan control module varies the voltage drop across the engine cooling fan motor in relation to the pulse width modulated signal. The cooling fan speed is affected by many different conditions and can be adjusted from 10-90 percent duty cycle. Ninety percent is considered high fan speed. When multiple cooling speed requests are received, the ECM uses the highest cooling fan speed of all the requests. During normal fan ON operation, the control circuit voltage will be low and near battery voltage when the fan is OFF.

Circuit/System Verification

Verify that the following DTC P1482 is not set.
⇒ If the DTC is set, refer to DTC P1482 .

Ignition ON, command the cooling fan speed from 0-100 percent with a scan tool. The fan speed should transition with the commanded states.
Circuit/System Testing
Important: The Circuit/System Verification must be performed first or misdiagnosis may result.

Ignition OFF, disconnect the connector from the cooling fan speed control module.
Ignition OFF, install a test lamp between the cooling fan speed control circuit terminal 6 and B+. The lamp should be OFF.
⇒ If the lamp is ON, test the cooling fan speed control circuit for a short to ground. If the circuit tests normal, replace the ECM.

Ignition ON, command the cooling fan speed from 0-100 percent with a scan tool. The brightness of the lamp should change with the commanded states.
⇒ If the lamp brightness does not change correctly, test the cooling fan speed control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

Ignition OFF, measure between the cooling fan speed control module ground circuit terminal 2 at the harness connector and ground for less than 1 ohm of resistance.
⇒ If greater than the specified range, repair the module ground circuit for open/high resistance.

Ignition OFF, verify that a test lamp illuminates between the B+ circuit terminal 3 and ground.
⇒ If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

Install appropriately fused jumpers between the cooling fan harness connector terminals 1 and 4 power and ground. The cooling fan should activate at full speed.
⇒ If the cooling fan does not activate, replace the cooling fan.

If the ECM, fan, and all circuits test normal, replace the cooling fan speed control module.

 

VCM Controls within VCM scanner. It will engage reverse lockout, turn the CEL on or off, engage the A/C clutch, etc... So it is definitely communicating with the PCM.

 

You checked this harness connector north of the relay. right?

 

My connector doesn't look like that, but yeah I checked all plugs, they look fine, and power is available at the PWM plug, because if I jump it, the fan starts and runs at full speed.

 

Connect a test light between terminals 2 &3 on the control module. it should light. Key on engine off, ground terminal 6 on the fan module. The fan should run full speed. If it does, connect a test light to battey positive and back probe terminal 6 and command the fan on thru it's duty cycle. The light shoul get progressively brighter. If you get no light, check continuity from ecm to fan module. the terminal at the ecm connector is C1 -58 and is dark green and terminal 6 at the fan module. PM me if you need more info or a schematic. There are also 2 inline connections for the battery feed and the ecm signal.

 

Sam:

It is communicating but what % are you running? Sometimes the simplest things are overlooked. I changed my connector with aluminum blocks (machine shop made) to avoid the melting issue and then insulated with shrink tubng.

It may be well worth taking to your local shop and have them hook up their scanner. It could still be yours.

PG

 

Sam, check again. I gaurantee this is your problem. Drivinfast is not talking about where it plugs into the fan module attached to the fan shroud. It's ~8" upstream of that. The middle connector gets loose and melts the harness.

http://forums.corvetteforum.com/c6-t...d-working.html

 

I checked, my plugs all look perfect. Remember I had the engine out; it was easy to get a good look at everything

I fired the car up today, and the fans started right up. No idea what is up with that; as far as I can tell it seems like when I command HP Tuners to turnthe fans on, it doesn't. But the ECU itself turns them on as per my fan speed vs coolant temp programming...
I guess the problem WAS the fan module, and since I replaced it, now it is fixed.
UNles this is a random intermittent problem. I'll report back if that is what it is. For now I think its solved.