I've been thinking, and trying to find information to either support or negate an idea I have. The idea is, and stay with me here, I have read a fair amount of information concerning the PCM's in these trucks being almost the same as the full size truck's or at least used on other V8 vehicles so I would imagine full size trucks would be part of that. A lot of those trucks have the tow/haul switch on the shifter for changing the shift pattern and firmness for towing trailers and such. If the thinking is right on the PCM, wouldn't at least the pins for the switch be there on our PCM since it's interchangeable? At that point, wouldn't it be possible to connect a switch and use that feature as well? Of course the programming for it may have to be enabled, but wouldn't that be possible by a place like PCMforless or wait4me? Anyone else ever wonder the same or look into it before?

Just kinda made sense to me, but then I could be WAY off base on this.

 

search I believe I did see a thread on this. also think about the 4.3 PCM full size silvy. they got a tow haul switch.. some one will know something but Im sure I read something on this site about it.

 

I've been searching on and off for a couple weeks on the topic both here and other places and haven't had any luck. Though I swear the search feature on many forums doesn't always work right....

 

I have only ever seen this option on a few GMC Jimmys... I believe that you would have to get your BCM and, most likely, PCM reprogrammed as when in tow/haul, you are basically working with a completely different tune. Everything can be modified and different between normal & tow/haul modes.

Here are a few pictures another member posted showing the tow/haul button in his 2001 Jimmy SLE:


The wire ties into the BCM which then communicates with the PCM. At the BCM, connector 1 (brown), pin B12 is the signal in from the tow/haul switch.

While I cannot find specific diagrams showing this switch in any of my references, I believe it is just a momentary grounding switch.

 

BCM eh? Nice. I'll have to see if I can find out where the BCM is located and go from there. I kinda figured the PCM would have to have some programming played with in it, was completely unaware of the BCM existing though.

Thank you sir! Your knowledge of these trucks is truly astounding.


EDIT: After searching about the interwebz on the BCM I've found it's location, and working on some wiring schematics. Thanks again!

 

My wife's 1999 GMC Jimmy has the "Tow" switch. My 1997 Blazer does NOT? Is this an option for Blazers and Jimmys? Is it an option for 1997 and 1999?

Also, does anyone know the details of "what changes" with the Tow in? Shift points? Ignition advance?

Thanks