96 Discovery Cruise Control and VSS Voltage Issue

[dishsoap1]

Hi Everyone,

I have owned my 96 Discovery 1 Automatic since 2004. I am relatively new to posting on this forum, but have read it plenty of times during Google searches. Ok, so a Cruise control question that there is hardly any information on. I am determined to fix the Cruise on this vehicle.

What i've done....

Replaced all vaccum lines and have no leaks.
I've used the Cruise control guides to test the set, decel, Brake pedal switches. Jumped the vac pump. All work. I pulled my CC ECU card out and found no visible defects. Ordered a used one on Ebay anyway, still no cruise.

Only issue left. When I use multimeter on CC ECU Connector to check VSS voltage. I get.... when sitting usually 0 volts, sometimes 12 volts. When moving, I get a constant 8.2 volts. No matter how fast I am going.

Speedometer works

ECM gives me speed when I hook my scanner up and drive around with live data running. Although it shows about 5-7 MPH slower than what speedo reads. Speed does not cut out irradicately on Scanner.

I've replaced VSS in past and I know symptoms of that going bad with cutting power to engine. I do not get any of that with current Sensor.

So, There is a circuit board behind the gauge cluster. This is supposed to smooth out the voltage pulses coming from the VSS. It then sends info to the Speedometer, ECM, Service Vehicle Module, and the Cruise Control ECU. Even though I am getting speed data to the speedo and ECM, maybe the signal being sent to the CC is no good.

So earlier, I pulled out my gauge cluster (relatively easy to do) and took a look at that circuit board. So far, no noticeable defects. My next step is to order a replacement board.

Does anyone know why I am only getting 8.2 volts? I have heard a couple people have this steady voltage issue, but no one would ever answer back. Hopefully, someone can relieve me of my aggravation. Thanks.

 

[discostew]

Most times it turns out to be the cruise module . When the cruise switch is turned on it should supply battery voltage to the vacuum pump on a white / blue wire . When a speed is set it will supply a ground path for the pump on brown / red wire , and closes the vent with a ground path on the brown and yellow wire . The cruise modules are hard to find in operating condition but there is , or was , a place called module masters that was rebuilding them . I usually find no battery voltage coming out of the module for that pump , and if you open it up the drivers are smoked .

 

[fishEH]

I wouldn't even bother with trying to find a good D1 ECU. The D2 ECU upgrade seems to work well for everybody that's tried it, myself included.
http://www.discoweb.org/forums/showthread.php?t=90799&referrerid=13769

 

[discostew]

I wouldn't even bother with trying to find a good D1 ECU. The D2 ECU upgrade seems to work well for everybody that's tried it, myself included.
http://www.discoweb.org/forums/showthread.php?t=90799&referrerid=13769

This is what I would do . I always just figure the module is burnt up . I cant remember diagnosing one that didn't end up needing it . You said you jumped the pump . It needs the module for power and ground.


I'm not sure what you have going on with that voltage on the VSS line but maybe see what it is without the ECU plugged in . If those drivers are burnt up the voltage might end up in a lot of places.

 

[p m]

To the OP - check the tech section. Conversion to D2/P38A cc box is covered in great detail.

 

[dishsoap1]

I have the ECU unplugged when I'm checking the voltage coming from the VSS/Buffer circuit board. So the 8.2 Volts is what is being sent to the ecu, not being scattered by a faulty ECU. The range is supposed to be 0-12 volts which vary depending on speed. If you only get a steady 8.2v, the CC ECU probably doesn't know how fast you are going and so it doesn't work. You guys might be right with it being bad ECU's, but i'm not quite convinced at the moment. I pretty much need someone with a D1 with working CC to check the Voltage going to their ECU plug from the VSS while driving around.

I will however, look into converting it to a DII system. Thanks for the help so far.

 

[dishsoap1]

Oh and that place still does rebuild CC ECu's. It's 65 bucks now.

http://www.ebay.com/itm/270414281347?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

 

[fishEH]

I have the ECU unplugged when I'm checking the voltage coming from the VSS/Buffer circuit board. So the 8.2 Volts is what is being sent to the ecu, not being scattered by a faulty ECU. The range is supposed to be 0-12 volts which vary depending on speed. If you only get a steady 8.2v, the CC ECU probably doesn't know how fast you are going and so it doesn't work. You guys might be right with it being bad ECU's, but i'm not quite convinced at the moment. I pretty much need someone with a D1 with working CC to check the Voltage going to their ECU plug from the VSS while driving around.

I will however, look into converting it to a DII system. Thanks for the help so far.

Hey Tim,
Where are you located? I have a plug n play D2 Cruise/pigtail on the shelf in my basement. I can let you try it out and it will tell you real quick if your ECU is crap(which it probably is).

 

[p m]

Oh and that place still does rebuild CC ECu's. It's 65 bucks now.

http://www.ebay.com/itm/270414281347?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I suspect this is where I got a replacement D1 cc box - but it was inop as well.

 

[discostew]

I see what your talking about on term 11 . Its described as a pulsing voltage that will change in frequency with vehicle speed . Maybe look at it as a % duty cycle or possibly hertz on your meter . You may not see much difference in that signal on just a dc volts scale .

 

[p m]

... or use AC scale on the DMM.

 

[dishsoap1]

I live in Plainfield, about an hour or so. I appreciate the offer. I am kind of digging the idea of making one myself, if I can't buy one already made up in the next couple days. I will be excited to get my cruise working again. I still like to drive it to work a couple days a week.

Also, today I bought on ebay a gauge cluster that also has that VSS circuit board on the back. Got it for like 20 bucks. I will try swapping that board out when it comes. If it still doesn't work, I will at least have a bunch of spare gauge bulbs, so win-win. I really hate that these trucks are all getting scrapped at such a high rate. Ebay is loaded with parts.

 

[dishsoap1]

... or use AC scale on the DMM.

I will try tinkering around with the multi-meter again, once I get that second circuit board I ordered put in.


If anyone feels up to it, maybe they can pull the ecu plug off their truck and put a multi-meter on it and see what they get. Would be cool to have that info for future reference. :applause: :applause::applause: I'll cheer you on with my emoticons. lol

 

[NorCalDisco1]

Hello dishsoap1,
Did you ever get your CC working?
I am also obsessed with getting mind working.
Just ordered a refurbished ECU from Roverland Parts and was told a little later by Atlantic British that I may have to have the refurbished ECU programmed as it will not match my VIN. WHAT?!?
Please let me know your current situation.
Thank you.

 

[discostew]

Hello dishsoap1,
Did you ever get your CC working?
I am also obsessed with getting mind working.
Just ordered a refurbished ECU from Roverland Parts and was told a little later by Atlantic British that I may have to have the refurbished ECU programmed as it will not match my VIN. WHAT?!?
Please let me know your current situation.
Thank you.

I don't think that's true . It's a plug and play module .

 

[fishEH]

Hello dishsoap1,
Did you ever get your CC working?
I am also obsessed with getting mind working.
Just ordered a refurbished ECU from Roverland Parts and was told a little later by Atlantic British that I may have to have the refurbished ECU programmed as it will not match my VIN. WHAT?!?
Please let me know your current situation.
Thank you.

I find that hard to believe considering the D2 ECU works in the D1.

 

[NorCalDisco1]

Can anyone tell me if accessing, removing and replacing the CC ECU is as supremely uncomfortable and frustrating as was the rear window ECU for that "easy fix"?

 

[discostew]

Flip open the glove box so it falls to the floor , that might make things easier . You need to pull the spring loaded plastic stop arm till it lines up with the opening then it will fold to the floor .

 

[NorCalDisco1]

Yes. That much is easy. I'm referring to accessing the actual ECU in that plastic box. Then having to pry-off the face plate. Then sliding out the board was perilous as it hits the glove box frame so you have to pull sideways and up which bends the board a little. Getting it to slide back into its receiving slots within the box was ridiculously tedious.
So the question is this. Is the CC ECU easily accessible and are the two screws holding it in place fairly easy to unscrew? Or are they buried and not visible?

 

[fishEH]

Yes. That much is easy. I'm referring to accessing the actual ECU in that plastic box. Then having to pry-off the face plate. Then sliding out the board was perilous as it hits the glove box frame so you have to pull sideways and up which bends the board a little. Getting it to slide back into its receiving slots within the box was ridiculously tedious.
So the question is this. Is the CC ECU easily accessible and are the two screws holding it in place fairly easy to unscrew? Or are they buried and not visible?

Its much easier to pull the whole ECU out than it is to slide the board out of the ECU box. :banghead:
My D2 Cruise ECU is just sorta tucked up outta the way. I wasn't going to bother messing around with some sort of permanent mount.