Two speed fan control in trucks

[PSWired]

I'm about to do the wiring for my electric fans to go along with my 2002 6L engine. I am using a 2002 truck PCM here. I'd like to have two speed fan control using two relays, but I'm not sure that the truck OSes support this. It looks like the f-body PCMs use Blue connector pin 42 for low speed fan control, and Red connector pin 33 for high speed fan control. On the trucks my wiring diagram says that Red 33 is used for A/C Recirculation door control. Frist, I don't see why the PCM would need to control the air recirculation door. Second, is it possible to set up two speed fan control using a truck OS?

I want the PCM to have full control over the fans. I don't want them running above a certain vehicle speed. Any suggestions besides just dealing with the 1 speed fan control? These fans are noisy at full speed!

[joecar]

I don't know how to configure your particular application,
but do be aware of this:
F-body uses 2 outputs to control 3 relays for two-speed fan control:

Fan1 output turns on relay 1 for low speed (fans in series).

Fan2/3 output turns on relays 2 and 3 for high speed (fans in parallel).

The PCM has parameters for setting the speed above which the fans turn off
(see System->Fans->Parameters).

[GMPX]

PSWired,

I will check for you that this is possible.
It might be hardcoded that if the platform is a truck then you cannot use the fans.
I'll post back my findings.

Cheers,
Ross

[PSWired]

Thanks GMPX. I appreciate the help.

Joecar, do you happen to have a link to the schematic for the relay configuration for 2 speed fan control? I haven't though about this much, is there any way to condense the function into two relays?

[GMPX]

The Holdens use two Fans and two relays, though one is driven from the BCM via a serial data message from the PCM so it is possible.

Anyway, it appears the PCM does not check the platform within the Fan control logic. However, we have had to add a calibration to allow you to disable the HVAC Recirc option, this will turn that output into a Fan#2 control only.
Interestingly, the Fan#2 output as well as being used for the HVAC output, it also can be used for the Engine Shutdown warning.
The Engine shutdown warnings will not work if you have the Fans configured as Series/Parallel.
The next update will contain the calibration you will need.

Cheers,
Ross

[PSWired]

Ross,
Thanks a million. When should we expect the next update to be available?

[joecar]

2001 F-body fan diagram...

...uh, how do I insert an image here...?

PSWired,
If you send me an email address I can send you the diagram
(I have it on CD and on a11data diy subscription).

[Steve Bryant]

Joe,
For inexplicable reasons, our ability to attach images and other files was stolen by a thief in the night about two weeks ago. Paul is working on it with the bulleting board folks. He even upgraded to the current version of the bulletin board software and the problem still exists.

They'll get it fixed, it just isn't fixed yet.

All my best,

Steve

[joecar]

Steve,
Stuff happens; thanks, sanity now improved a little.

[GMPX]

Ross,
Thanks a million. When should we expect the next update to be available?

Beta testers have it right now, so very shortly.