Is the os in a 01 truck pcm capable of running high and low fan outputs using hpt. Or am I limited to a single speed. I was wanting to hook them up using high and low to reduce the electrical load on the electrical system at startup.

 

not really . . . you can run low full time, and set the high temp, and then run them on high.

Search my name if you want to make your own harness.

 

So the fan would be running all the time on low- regardless of temperature then kick up to high when temps rise?

 

yep, or splice into your a/c, and let that control the high

I have mine on low 24-7, with a manual switch for the highway, and or high. It's a double position switch.

 

My fan setup is like this:

Engine gets up to temp: 1 fan on low.
Engines gets up to set temp in the PCM (196*): both fans on low.
Engine at temp and a/c on: both fans on high.
Speeds >40 mph: fans off.

This is with a Nelson harness with 3 relays and HPTuners.

 

Mine come on like this:
Engine on A/C reaches max pressure both Fans Low
Engine on Temp (210) reached both Fans Low
Engine on over heated (240) (don't really know, never did it) both Fans High


Factory Fan Harness
Will fit most trucks and can be used with out lights flickering from A/C cycling fans every time the A/C starts , common problem with after market harnesses .

 

on the nelsons 3 relay harness if your computer wont turn on fans,you can wire a switch to the blue wire that goes to terminal 42 0n pcm to ground.this will turn on both fans on low.and green wire that goes to ac wire can also be wired to a swicth to battery voltage and this will turn on one fan high.and if you have both switchs on,both fans go on high for good cooling.

 

So basically the pcm only has the capability of one fan relay output then you have to use either the a/c request or a manual switch to control the additional speed be it high or low depending on how you wire it up then?

 

it works off of "signals" meaning you can have one wire turning on one or two relays.

You use the PCM for one relay, both fans on low, and the A/C "trigger" wire for the other two relays.

 

Fans work off ground from PCM , so grounding makes the fan activate .

Factory Harness

Picture of top Factory

Fuse Box where harness goes Harness snaps right in the right hand side of fuse box .

If your fuse box looks like this it will work