This topic has been covered many times on here but no one addresses the year of PCM's. We know the 411 PCM is pin 71 for the tow haul switch. Is it the same for 2004 silverado PCM. I have the switch and want to wire it up but no definitive answer if it will work.

 

Yes, C1-71.

Jeff

 

hmm ill give it a try. Philtx over at the s10forum said he couldnt get his to work, but ended up have a new bcm flashed. we'll see if its legit late spring when she's running again.

 

The pcm will only respond to tow haul if the pcm is flashed with a truck vin. If it's not a truck VIN you are SOL cause the trans tables for tow haul are not there.

 

luckily I have the vin from the silverado in my Ecm.

 

The 04 silverado pcm differs from the 411 in the way tow haul functions. On the 411 pcm it is very possible that tow haul would still function because the pcm shares the same communication architecture the BCM is designed to communicate with because the 411 pcm was used in the S series platform with a v6. It talks over a specialized comm circuit called UART that is different than the standard low speed bus. It is over the uart circuit that theft deterent info and tow haul is commuicated from the bcm to the pcm and vice versa.

In order for it to stand a chance to work you have 2 things happen the yellow UART comm circuit must be intact from the connector C2 pin A1 bcm to location C1 pin 58 of the pcm this is the UART serial comm circuit and your truck has to have a tow haul switch already.

If it does not have a OE installed tow haul switch then the BCM must be flashed to a S series truck as close to yours in options as you can get that is the same year model and has the tow haul option. This enables tow haul functionality in bcm once it is flashed with the correct calibrations by reprogramming your existing BCM with the VIN of a vehicle that matches the above.

2ndly you have to install and run the wiring for the tow haul switch from the bcm to the switch which will be BCM C1 pin 12 from bcm to tow haul switch pin A then tow haul switch pin B has to be body grounded. This provides the towhaul input to the bcm and then the bcm broadcasts the tow haul command to the pcm over the UART serial communication circuit.

So in closing
pcm has to have truck vin
BCM has to have UART comm correctly hooked up
BCM has to be correctly flashed for vin with tow haul if not present alreadyo
BCM has to have tow haul switch correctly hooked up

D I guarantee all the above is true for a 411 pcm cause I had it functioning on my LS swapped sonoma. In theory it should work with the newer pcm but if it doesn't it's due to the difference's in the 04's internal communication mismatch to your existing BCM.

 

The tow haul will work with a cars pcm but the performance tables have to be populated in the tune .

 

The switch will work but only while holding it like a nitrous switch , not an on off like Oem setup.