JustinSS can reflash you PCM for can control,,,,,,,,,,,

 

No, the PCM has the ability to control two relays. Pin 42 on the Blue harness, Pin 33 on the Red/Green harness.

 

So the 2001 operating system has the capability to control high and low fans using the high and low fan relay outputs as it does in an f body as long as they are enabled using a tuning suite such as HPT. Both outputs just have to be turned on using a tuning program. The reason this is causing a fuss is because I have talked to a couple of custom tuners that have said the 01'os could only turn on one fan output and you could use it for either high or low and then you would have to either wire a switch or have the a/c request turn on high speed. I am wanting the pcm to make the decision of when to use high and low speed without all of the extra crap switches etc. I figured there had to be a way to turn on both outputs because it is the same pcm that is used in fbody's and vets and they use a high and low fan relay output. I know how to wire the damm thing I'm an electrical engineer and was a mechanic first. It's just getting a straight story out of "knowledgeable tuners" on if they could enable both the high and low pins in the pcm. Everybody keeps telling me that only 04' up truck operating systems are capable of controlling high and low speed. Usineg pin 43 and 33 is one the high speed and the other low speed or does it energize both outputs simultaneously on a call for fans to operate.

 

Have you actually *looked* at your pcm? Red 33 is already connected. It goes to the recirc door control motor in the A/C system (info in service manual).

It appears that some engineer decided to steal an extra output from the fan system - after all, trucks don't have fans. The table data is there simply because they didn't need to change it in order to get the job done. Just drop in a different code module (just in case for aux fans) but still reference the standard header definitions.

Maybe there are some models that don't do it that way, but I'm out of luck on mine.

 

I have not had time yet to look up the pinout on alldata for the older trucks at the shop yet. Well crap guess that answers the question I was hunting. It also explains why on my 98 big block when the auxiliary fan comes on it automatically switches the a/c into recirculate.

 

Now that you mention it, I do recall seeing that on an 02 I recently tuned. 12216125. You have the ability to alter what that pin output controls using EFILive. It is in the System calibration and the
A/C and then Parameters and then "A/C Auto Recirculation".

 

Now *that's* interesting. I wonder if they can change it to a different output pin (maybe something useless like egr pintle)? I'd kinda like to keep the A/C recirc function intact - especially this time of year.

 

don't the 05s and up come with fans?

 

Actually, I meant just the 99-02's. 03-04 has both pins available. And of course 05+ comes with the darn things.

 

Look at pin16 , it was fan high on some .
Pins (42 , 33 , 16) are ground not power .