tow/haul switch is it possible on a 5.7 1998 vortec pcm

[Eric]

Hi Eric here , relating to my friends 1998 5.7 vortec pickup , i am wondering if i can select like a tow/haul mode with this pcm , is there a pin on the pcm that i can toggle to ground or somehow to switch to a different transmission setting like on my 2000 4.8l, i noticed in the tune under speedometer parameters there is an on off option for something like a tow haul and in some of the transmission tables like pressure and shift times there is normal and economy , can this be done , i have the gm sevice manual on dvd but cant seem to find it on the vcm pin outs , but in 2000 the tow/ haul switch goes first to the bcm but i believe it can be sent to the pcm directly , anyone no about this or have done this with a 98 5.7 pcm , please do get back , thank you eric

[Taz]

Hello Eric,

In an OEM configuration Tow / Haul (Performance) mode is activated by a momentary (spring loaded) switch. When the switch is depressed it briefly grounds a circuit of the BCM - “telling” the BCM to change to / or from Tow Haul mode. The BCM sends a serial data (Class 2) message to the PCM and IPC. This message “tells” the PCM to change transmission shift patterns. This message “tells” the IPC to turn on / turn off the Tow / Haul indicator lamp.

I don’t do Vortec “Black Box” PCM tuning, so the following are merely suggestions of two possible courses of action.

Obtain the “pinouts” for the BCM in the 1998 truck. Determine the BCM pin (wire) for the Tow / Haul switch (for 1999 trucks it was BCM connector C1 pin B12). Connect one side of a momentary switch to this pin, and the other side of the switch to ground.

Then experiment to see if this switch will activate Tow / Haul mode. You may (or may not) need to change the value of H4595 in the tune as well.

If this doesn’t work, then an alternative would be a PCM upgrade - often referred to as a “0411 swap”. This involves replacing the Black Box Vortec PCM with a 2001 or 2002 LS1-B style PCM (service number 12200411). This PCM will support Tow / Haul mode and other additional features that are not supported with the current PCM.


Regards,
Taz

[Eric]

thanks Taz i will try this , it is my friends truck so if it does not work i dout he will change over to the 0411 but i have heard alot about this swap , by the way it must be a pretty complex swap because the connectors are not the same but for someone who wants more controle of the tune it is a very good idea, wouldnt the pinouts of the 99 be the same as the 98 , i will check , thanks eric

[Taz]

The 1999 1500 series trucks were a new model design - I have no idea if the BCM pinouts are the same as the 1998 model year.

The 0411 swap is very straight forward. The Black Box Vortec PCM has 4 connectors, the LS1-B PCM has 2 connectors. The “pins” of both connectors are the same. You simply release the pin from Vortec connector, and insert it into the appropriate cavity of the LS1-B connector.

The required tune to make the swap work is from a 2001 or 2002 Express / Savana van - that was originally equipped with a 5.7 L Vortec engine and 4L60 or 4L80 transmission.


Regards,
Taz

[Eric]

Hello Eric,

In an OEM configuration Tow / Haul (Performance) mode is activated by a momentary (spring loaded) switch. When the switch is depressed it briefly grounds a circuit of the BCM - “telling” the BCM to change to / or from Tow Haul mode. The BCM sends a serial data (Class 2) message to the PCM and IPC. This message “tells” the PCM to change transmission shift patterns. This message “tells” the IPC to turn on / turn off the Tow / Haul indicator lamp.

I don’t do Vortec “Black Box” PCM tuning, so the following are merely suggestions of two possible courses of action.

Obtain the “pinouts” for the BCM in the 1998 truck. Determine the BCM pin (wire) for the Tow / Haul switch (for 1999 trucks it was BCM connector C1 pin B12). Connect one side of a momentary switch to this pin, and the other side of the switch to ground.

Then experiment to see if this switch will activate Tow / Haul mode. You may (or may not) need to change the value of H4595 in the tune as well.

If this doesn’t work, then an alternative would be a PCM upgrade - often referred to as a “0411 swap”. This involves replacing the Black Box Vortec PCM with a 2001 or 2002 LS1-B style PCM (service number 12200411). This PCM will support Tow / Haul mode and other additional features that are not supported with the current PCM.


Regards,
Taz

Hi taz eric here , just checked the connector end views for the bcm , C1 pin B12 is the actual pin on the bcm connector because i found the connector end views in my Ac delco service information dvd and all i could see was pin d12 that was not used so when connected would conect to B12 on the bcm and this was for the 99 bcm as you stated , if i try and find the connector end views for a 98 bcm i get nothing , does this all make sence to you , do you use the delco dvd , i ask because i find it a pain to use , maybe because i dont use it enuf to get familliar with it , thanks Taz Eric

[Taz]

I’m old school (or just old !) - I purchase GM shop manuals as necessary for projects - I prefer printed material to a computer screen.

I don’t have a manual for a 1998 truck. If you are unable to find a “Tow / Haul” circuit in the wiring diagrams / BCM connector end views of a 1998 truck - perhaps this was not an option - I’m not sure.

I noticed in the 1998 Vortec tunes there is an “Economy” set of shift tables. Perhaps look for a “Tow / Haul” or “Economy” or “Performance” switch / circuit - again, these may not exist.


Regards,
Taz

[Eric]

thanks Taz , ya i here you on old school , i also like paper but i thought it would be nice to have it on dvd considering my two gm vehicles but i find the dvd very long to use and to find specific information , i guess i just have to use it more often to get the beat of it but it has been very helpful a few times already , i will look again for something that could resemble this circuit , but i wonder why would there be tables for economy if there wasnt a way to select them , it may just be an option that you toggle on in the tune and the vcm can select it when needed , because like i said before in the speedometer parameters there is an on off toggle for something that resembles this , i will have to see, eric i should be concentrating on my own ride

[redfury]

Perhaps the 2 tunes are in there for the adaptive learning capability of the PCM. If the driver is easy on the vehicle and doesn't put much of a load on it, it goes into an economy tune, but if it starts to see the vehicle put under a more consistent load, then it switches to more aggressive shift tuning through the PCM. That's just a guess, but would seem plausible if both modes are present within the black box.