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LS6 swap in progress.
1999 LS6 Sonoma on C5 Brakes
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Discussion Starter · #1 · (Edited)
Hey all - wondering if anyone has encountered this before. Since 2014 I have been running an LS6 with Corvette DBW throttle body & pedal setup in my 99 Sonoma. Cruise has been functional using the DBW module and Corvette PCM. ABS wasn’t working due to staggered wheel setup so I set out to remove it earlier this year. Light would turn on after going above ~10mph.

Fast forward to present day, I deleted the ABS and added hydroboost since my cyl 7 ignition coil started hitting the vacuum booster. Cruise no longer works, ABS light on immediately at key on. “Cruise Lockout” bit in HPTuners always stays “yes”, but the other buttons (except “Set/coast”) are registering. I jumpered the purple brake switch circuit that’s on the ABS connector and still no luck. All fuses intact.

So three questions:

1) Does anyone know if the ABS module has to be present on a DBW system to allow cruise? On other S10 ABS deletes it seems like people don’t have an issue with cruise.
2) Could there be something goofy going on with my brake switch that I messed up when putting in hydroboost? Rear brake lamps and CHMSL works.
3) I removed the ABS computer from the motor & solenoids and plugged it back in and still no cruise…ABS lamp on immediately at startup still. No ABS codes with my advanced scanner though…there was a general U1255 loss of communication but I cleared that and still have ABS lamp/no cruise.
 

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Been there Done it
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If your brake pedal is not fully returning to where it was before you added the hydro boost you won't have cruise. The brake switch is a double reverse action switch. It makes a circuit to the brake lights, but it also breaks a circuit to the PCM. If the PCM is not getting that 12v from the brake switch it won't allow cruise because it thinks you have the brakes applied. If you look at your wiring diagrams you'll see the BPP switch signal to the PCM.
 

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LS6 swap in progress.
1999 LS6 Sonoma on C5 Brakes
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315 Posts
Discussion Starter · #3 ·
If your brake pedal is not fully returning to where it was before you added the hydro boost you won't have cruise. The brake switch is a double reverse action switch. It makes a circuit to the brake lights, but it also breaks a circuit to the PCM. If the PCM is not getting that 12v from the brake switch it won't allow cruise because it thinks you have the brakes applied. If you look at your wiring diagrams you'll see the BPP switch signal to the PCM.
Thank you! I will look into this. It must be right on the edge because with the little bit of lash between the pin on the brake pedal and the clevis on the hydroboost I can see when the brake light switch gets asserted but it’s hard to tell if it fully returns.

In the past with this DBW setup I have noticed if I don’t put on the brakes before trying to enable cruise it won’t engage…maybe this means the switch also needs to assert as a closed circuit to get it out of cruise inhibit as well.
 

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Been there Done it
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12,477 Posts
Sounds like the switch could be flaky.
Not getting the 12v to the PCM can also cause no TCC lockup.
 

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how is the LS wired into the truck? stand alone? or merged into the factory S10 harness?
i have nearly the exact same set up, and i have cruise. Im going to guess your BLS isnt adjusted correclty since it worked before going hydrobosot
 

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LS6 swap in progress.
1999 LS6 Sonoma on C5 Brakes
Joined
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315 Posts
Discussion Starter · #6 ·
how is the LS wired into the truck? stand alone? or merged into the factory S10 harness?
i have nearly the exact same set up, and i have cruise. Im going to guess your BLS isnt adjusted correclty since it worked before going hydrobosot
Thanks for the input - I wired it into the truck via the C101 and fuse box + separate cruise circuits into the DBW module and PCM where needed. Really has worked well since the beginning.

I think my switch may have been going and switching over to hydroboost was enough to make a difference. I recall seeing my trailer brake light turning on and off while braking so I might just start with the switch and go from there.

Did you delete ABS?
 

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LS6 swap in progress.
1999 LS6 Sonoma on C5 Brakes
Joined
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315 Posts
Discussion Starter · #7 ·
Did some probing today and brake switch works, but I found a couple of wires had broken at the terminals in the connector I added to splice the Sonoma cruise switch circuits to the DBW. I must have tugged them while pulling the old booster. Need to get some replacement terminals then will let everyone know how it turns out.
 

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That would definitely effect what works and what doesn't. I added a similar connector on mine. I think I spent more on the correct crimping pliers than on the connector and terminals. IIRC those wires should be double crimped. Once on the actual wire and once on the insulation for support. My fancy pliers had separate sections for each type crimp.
 
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LS6 swap in progress.
1999 LS6 Sonoma on C5 Brakes
Joined
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315 Posts
Discussion Starter · #10 ·
That would definitely effect what works and what doesn't. I added a similar connector on mine. I think I spent more on the correct crimping pliers than on the connector and terminals. IIRC those wires should be double crimped. Once on the actual wire and once on the insulation for support. My fancy pliers had separate sections for each type crimp.
That’s what I used as well but I think I used too small a size of the conductor crimp and probably damaged the copper with how tight it squeezed. Lesson learned!
 

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LS6 swap in progress.
1999 LS6 Sonoma on C5 Brakes
Joined
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315 Posts
Discussion Starter · #11 ·
Well I fixed the terminals and all of the buttons register in HPT now but cruise is still being inhibited. I am beginning to wonder if my ABS module was providing some output to the PCM (running 2002 silverado OS) that enabled DBW cruise. I will get to the PCM connections tomorrow or Thursday to confirm the TCC Brake switch is asserting properly.

If that doesn’t work, I may just plug the ABS computer in without the valve body again and see how that goes now that my stalk switch connections are good.
 

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LS6 swap in progress.
1999 LS6 Sonoma on C5 Brakes
Joined
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315 Posts
Discussion Starter · #12 ·
I will chalk this issue up to a series of unfortunate events and will post my learning for posterity sake.

Started out today by probing the TCC lockup wires coming out if the C101 connector…no voltage in the normal/non-brake asserted state. > Hmm ok so it must be a bad brake switch
Pulled brake switch off, no voltage going into the normally closed switch contacts, but brake lamps still work
wtf.exe
harness schematics say ABS fuse on side of dash feeds the vbatt to this circuit on the brake switch
replace fuse and voila, cruise works again!
I swear the fuse was good when I checked it at the start of this whole debacle, but that was before I found the broken wires on the 6-way connector. The fuse probably popped after moving wires around when I plugged the ABS back in to see if it would fix the issue.

Merciful heavens, I can now thrash with an LSD, brakes that stop amazingly and cruise control. Thanks for the input all.
 

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Been there Done it
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12,477 Posts
Thanks for letting us know what fixed it. Some one down the road will be helped. As you pointed out it was probably the damaged connector wires that blew the fuse. I guess a good lesson is to always re-check the fuses after repairing any wiring.
 
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