Cooling Fan Issue

What have you done so far? Looks like pin 6 of the PCM is the ground control for the high speed relay. Connect a scanner and look for relevant data PIDs and see if the fan is being commanded on. If it is,you have a bad input to the PCM. If it isnt you probably have a bad PCM. There should be no B- on pin 6 if there is no "on" command.

I looked at that diagram and can't possibly see how it could be correct. Without getting too deep the Daimler PCM sends a pulse width signal to the cooling fans, but this car seems to have a brushed motor with high/low like a wiper? The problem you describe is quite common with Daimler PCMs. As the vehicles aged there was voltage drop that developed in the ground return on the fan motors. Since

I would check some other diagrams. In the diagram you posted it looks like the low speed fan can never run on it's own. That doesn't seem right. Plus, the control side of the high speed relay is in series with the motor? I'm a little confused by this diagram also. It just doesn't look right.

Bob, even the color wiring diagram is drawn the same way. Either they have changed the laws of electricity, or someone missed something when the diagrams were drawn. Even the motor wiring diagram is drawn the same way. So I guess that brings me to the question, how many wires go to the blower motor, and is there actually a high speed and low speed relays in the relay center?

I agree. Even the older GM three relay cooling fan setup didn't have the control side of the relay in the same circuit as the load.

I agree with others , bad diagram, I took a look at other diagrams and see the primary side of the relay being B+ CKT 20 in Run and crank while the PCM is ground side control.

That is quite an interesting circuit. I was looking at another diagram and it is same. Pin 2 on motor runs through a circuit breaker to ground. So therefore, could there be a reversal of current flow through the high speed relay coil after motor starts to spin? Ground enters through pin 2 on motor out on pin 1, PCM turns on high speed relay with 12v+ on pin 6 of pcm, this energizes Low relay

For sure a difference a difference in SI, The diagrams that I see that have the complete circuit match the example above, then some OE info shows both ways? Maybe a mid year change? Mathew let us know what you find.

Hi Matthew: EDIT: Now that it's been pointed out I was suffering from Cranial-Rectal Inversion, I grabbed a diagram similar to what Bob posted. This one make sense. Sorry about the earlier screw up. HTH, Guido

That is not the correct motor. He's looking at the cooling fan, not the interior blower motor.

Can you say DUH! Thanks, I've edited my post. Guido

Haha tell me about it. I left mine up for all the world to see my shame. Next time no trying to help someone 5 mins before closing........

Matt, I think this diagram makes more sense. It's from a PT cruiser so the pinouts may be different but I believe this is an accurate representation of how the circuit would be wired.

That's what I would expect to see. I wonder where the other diagram came from... There's not even a load on one circuit.

That diagram must have been redrawn by someone on crack.

Had a conversation about this issue once with a retired engineer, IIRC. Basically, it's no different than proofreading those "papers" you had to write in High School or college. No matter how many times you look at it, there can still be a mistake. Then factor in that it gets sent out to someone else to get printed, and then published, etc. By the time he was done explaining it, I felt luck

Hi Geoff: I'd say that I found this article informative when I read it but that would indicate that some of my hair is getting the color of Jorge's. While the circuits may be more complicated, the concept still holds. Dumb it down, intelligently. resources​.​aeswave​.​com/articles/Jorge…​.​pdf HTH, Guido

helps with what? I was talking about publishing errors.

Hi Geoff: I think this line illustrates it. "From the contradiction, can we conclude that the diagram is either incomplete or simply incorrect?" Years ago, I remember seeing a schematic of a (GM?) starting circuit. (It may've been in an ATG manual.) There was a diode facing a diode. In that …e, which part, if any, of the schematic would be correct? (rh) I wasn't disagreeing with you…

Guido, I remember finding that article in a stack of older motor age magazines at the Sunoco I worked at. I photocopied it and still have it in my toolbox. Thanks for supplying that, it made my morning. It's the small things I guess.

When I am reasonably sure a diagram is wrong I will usually look for one year newer or older or look-up another model that I think might use the same system.

The diagrams are wrong. I wouldn’t lose too much time staring at this diagram. You know the power is shared between the two relays and the PCM supplies the ground. If you don’t have a short to ground on the high speed relay at pin 6 of C3 connector when disconnected, but a ground is present when the C3 connector is plugged up and KOEO or KOER and scan data says the high speed fan is off, then

This picture from FCA may help.

And the low speed...

Almost 1 of April here, so let's try to something fun: redraw the diagram in GIMP. The resulting diagram is an improved 2-speed motor control, where the low speed control is automatically disengaged if the high speed kicks in. youtu​.​be/enMPwB_rCUc

Dmitriy That is fantastic! Made my morning with the most appropriate sound track! This reminds us all that the industry at times can be a circus!

love everyone's comments. of course this wiring diagram is not correct. the pcm was replaced on this vehicle and dtc did not return.

Hello Matthew, Did the vehicle have a low and high relay or was it a PWM control from the PCM ecu? Reason I ask is the PWM controls on the Daimler vehicles get damaged because of a poor design of the ground returns. If the car develops this problem it will blow out the new PCM. Generally happens when the fan is run up to 100%. Develops a voltage drop at the fan control unit. Then some of the