I have a 2005 Crossfire and the radiator fan didn't work so I replaced the controller. All good for about 1 month.
Then, it stopped working. New controller and it still doesn't work.
Fuses and fan itself are ok as I can get it to work by jumping through the harness.

Other headscratcher is that the air conditioning only works when the car is moving. The compressor will kick in for a second without driving but won't cool it.
If I drive, any speed, the air con works fine.
I feel that these must be related as they happened at the same time.

Any suggestions other than just replacing the PCM?

 

If the engine fan does not run when the A/C is on, the A/C cant rid it's condenser of heat, therefore, it cant take heat out of the air in the cabin, so that makes sense.
When you MOVE the car, air flows over the condsenser anyway so of course the air out of the vents turns cold. No mystery there. The mystery is: "Why won't the damn fan run?"

The ECU/FCM relationship is simple in concept, but sometimes we see failures that make no sense.

Here is how it all works:
The ECU sends "tickle pulses" to the FCM. The FCM responds with an "I'm here" pulse. If the ECU wants the fan to spin, it widens its tickle pulse in proportion to how fast it wants the fan to run. The FCM sends a pulse back to say "Im not only here, but I will obey".

• If the ECU does not get an acknowledgement pulse back, it knows the FCM is in trouble or broken - so it lights the little radiator light on the left side of the instrument panel.
• If the FCM sends a modified (Wider) pulse back, the ECU knows this means the FCM is having issues or sees improper current (too high or too low) going to the fan motor - so it lights the little radiator light on the left side of the instrument panel.
• If the FCM does not get a tickle pulse from the ECU, it enters "Emergency mode" and spins the fan at warp drive speed to protect the engine from overheating.

Thats how it works. ANytime you see that light, the owner's manual tells you to take the car to a dealer and write them a blank check. Make sure you NEVER do that.

There are six wires going to the FCM.
Two huge red/black battery feeds, the red is fused in the little black box next to the battery at 50 amps and is labeled for the Fan.
Two huge red/black feeds to the fan motor.
One little wire called "Ign" that supplies "wake the hell up" power from the actual contacts on the ignition switch.
One little wire called "pwm" that is the bi-directional signal wire to the ECU.

Something I just learned after all these years: If you cut the pwm wire and ground the end going to the FCM, the fan should run. This is a built in diagnostic in the FCM. DO NOT ground the end going to the ECU.

First question for you: Is your little radiator light on? If it is not on, cut the pwm wire, if the light still does not come on the ECU is bad or the light is burned out. If the light does come on, this means the ECU seems to be OK and your FCM is bad.

THe big question is: Is the 50amp fuse good? (Must be if you jumpered around the FCM and the motor ran.) So, is the little radiator light on or coming on at times? If so I'd blame the FCM, if not I"d lean towards the ECU but ECU failures are super rare.

 

Ok - thanks for you detailed message.

The more I look at this the more confusing it is.

If I cut that grey wire, no radiator light comes on. However, equally confusing is if I ground the grey wire going into the harness, it doesn't turn the fan on.
As I said, the fan does work on high if I bypass everything and run power and ground to it through the live wires on the harness.

P.S. I have both a gray wire and a red/white little wire going into it.

What next?

 

You do not ground the wire going to the ECU, you ground the wire going to the FCM. Make sure you are grounding the right "half".
The fact you can cut that wire and not get a light bothers me, that is NOT normal behavior. In fact, I have a switch under the dash that I can use to open the connection, I get the light and the fan goes to ward speed. I use this to keep the A/C super cool in stopped Dallas city traffic. I call it my "instant cool" mod.

That light is either burned out or the ECU has a REAL problem. But again, the fan module should run the fan at high speed anytime the wire is cut. Grounding it should NOT be needed at all. If the FCM dos not see pulses from the ECU, it goes into emergency mode. Let's look at it this way, ya gotta get the FCM to act normally. Sounds to me like your FCM is bad.

Now, again, make sure you have 12 volts on the IGN lead to the FCM. The fan wont run unless you have 12 volts on the IGN wire to the FCM AND on the Big, fat, red wire.

 

Just get the FCM to run like it should, if problems persist after that, you need an ECU. There are places to have the ECU fixed, which is good, because a new one is around $2400. Josh at the MSS can re-map a used one to your car, if it comes to that, I'd expect the used ECU and Josh's programming to total around $500. But let's get the FCM to act right first, if it does not turn the fan on it's own with the PWM wire to the ECU disconnected, the FCM is bad or you have no power to either the Red cable or the little IGN lead. Simple as that.

 

This is my second FCM - brand new.
The first one worked for a short period and now this new one doesn't work at all.

I was sure to ground the correct side of the cut wire (going into the harness not back to the ECU). It does nothing at all.
Yet if I just jump on the harness, the ground to ground to fan and power to power to fan it turns the fan on very high.

When I check at the harness, the small red/***** wire is power all the time and the gray wire seems to be ground. I am still unsure why I have a small red/white wire in addition to the gray one that goes into the FCM. I agree that I should get the FCM working correctly first and only then go back to the ECU. However, I bought two brand new FCMs and still doesn't work.
Seems like I have such a strange issue and not the normal type problem on this thing.

 

Ok - so I hooked the first new FCM I bought back up and what happens is the fan comes on fast and then stops, if I cut the grey wire nothing happens, ground the grey wire nothing happens, but every once in a while the fan goes very high for a few seconds and then stops.

I assume this could be both the ECM and FCM? I ordered another FCM - this time a used one as no luck with the two new ones I had.

 

There are switches in the A/C system that shuts the system down when the pressure is not correct, or the drier is bad. Perhaps a switch is opening and shutting your A/C system down?