98 S10 cruise control
 

The cruise control on my 98 S10 wasn't working so I did some troubleshooting and determined the ground wire on the under hood module was open. It works when I ground the black/white wire. Since I can't shut my DLR off by pushing the dome override button, I thought they may share a ground. I saw a wiring diagram that says the ground goes to through the under hood bussed center, but I can't figure out where. I can easily just splice the ground wire to a new ground, but I'd like to fix the break itself and maybe fix something else in the process. Can someone point me to where the ground from the cruise module under the hood makes it's connection?

That ground joins up with the electronic brake control module in the under hood bussed electrical center then it goes on to join a dozen functions before going to one of the rear block grounds. If it was a problem towards the block ground you would have a catastrophic number of failures so it’s either a dedicated cruise control module problem or it also involves the brakes. Either way you have two choices, start cutting back the electrical tape wrap on your way to the bussed center then picking up the bussed center to see what’s going on (my bet) or just running a solid clean wire to a block ground. I caution you that if you pick up that buss center that may result in many additional problems if there is corrosion. That would allow you to properly fix any future issues now but your truck may go down for a while. So it depends on your goals: leave well enough alone and get back on the road until the next problem or risk pulling on the sweater thread that goes on for a while. When I was 25 I’d be in there with jackhammer and an all nighter but at 70 I would fix the cruise control and get back to something else. Youth is wasted on the young. Lol.

George

Thanks George. I'm probably just going to splice a wire to ground. I've got the FSM GM Service manuals (the one that's on a CD and covers every year of GM vehicles thru 2004) and it allows a key word search. This ground wire is apparently circuit no. 451. But, you can't search 451 to see what else is on the circuit. Frustrating. The schematic I found for the cruise control system doesn't even show the ground, so I'm working off something someone posted on the internet. Its probably close, but who knows. The ground goes into connector C1 on the fuse block and comes out of C2 and goes to ground through connector C2. I'd rather not disturb the rat's nest of wires under the fuse block especially since I have no apparent problem with the brakes. I'm not quite sure what problems GM had with its QC with regard to solder joints. I had a 96 S10 that never ran right -- it would stall, slam into gear etc. Turns out that 20 years after it was made, no one ever caught that it didn't have its computer wiring fixed due to lack of solder internally to a ground connection. I finally figured out which TSB applied and the truck ran great after the fix. This could be simple corrosion, but I've found you never really know with GM.

The blk/wht ground wire exists the cruise control module on pin F as circuit 451 then enters the connector at the fuse center on c1/e7 then exits the connector on c2/e7 also on blk/wht to S152 where it joins a dozen other grounds then on to the engine ground at ground point G117.


George

Thanks again. I have another fuse block question. n I've attached a screen grab from a YouTube video because I don't have a picture of my fuse box, but what is the circled post for? I thought mine might be missing a nut, but I see that this one is also without a nut. I'm guessing trailer brakes?
https://cimg8.ibsrv.net/gimg/blazerf...73e6b2d557.jpg
Just wondering why it is all alone with no nut. I though initially this might have something to do with the ground, but I suppose not.

Pages 332 and 333:

https://www.carmanual.org/chevrolet-...s-manual-2065/


George

I'm still dealing with the cruise control. I fixed the ground wire and question whether that was even an issue to begin with. It's an intermittent problem. I've run the tests on the stalk switch and the brake pedal switch and everything tests out with the proper voltages. This is consistent whether the cruise control is not working or if it is working. I figure it has to be something other than the multifunction switch or the brake switch. I'm considering whether it can be the input from the VSS through the ECU. I guess I'm looking for a square wave on the lt blue/black wire, but I don't have a scope. I do see 4.5 volts on that wire (pin K) when the vehicle is moving and zero when it is stationary. The speedometer has always worked fine. Therefore I don't believe it can be a VSS issue, but maybe a cruise control module issue or some corrosion in The wire running from the ECU to the cruise control module. Probably most likely a bad cruise control module at this point, but I thought I would throw it out there for input.

How is your cruise control misbehaving? Won't engage, engages but releases, does not hold speed, etc.

George

Most of the time, it just won't engage. When it does engage, it works fine.

Intermittent problems can be a challenge and thats why they send a lot of people to the parts cannon. We know that the system can work properly so there is not a hard failure, the question is what gets wonky when it won't engage? The fact that it never releases on its own and the speedometer function is solid suggests that its not the brake switch, VSS or clutch switch if so equipped so I would put those last. That leaves a lot of possibilities:

1. Powers and grounds
2. Engine computer
3. Cruise control module
4. Wiring
5. Cruise switch

The cheapest step is to inspect all wiring, connectors and grounds first. After that the primary candidate is the cruise switch. Two choices, rig up a meter to be able to see whats going on when it wont engage to confirm the switch or replace the switch. Let me know if you want to get fancy and try to catch the switch with a digital multimeter.


George