What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Vss issue after DD gauge swap

P

Plunkett

Registered Member
Joined
Jun 22, 2010
Posts
7
Reaction score
1
Location
Ringgold, GA
So I’ve got a 87 GMC Sierra with a 350/700r4. I replaced my stock gauges with a set of Dakota Digital HDX gauges. I now have an electronic speedometer. The problem I’m having is that the original speedometer has three wires going off of it to a speed sensor (light green box). I’ll attach a picture of what I’m taking about but originally it was a green, red, and black wire coming off the back of the speedometer. How do I need to wire this up to get my vss to work and not show a code 24 anymore.

42726120-922E-44E5-AB03-3F63559A2660.jpeg
 
The ECM is looking for a 2000PPM signal on pin A10 at the ECM.

Either run a DRAC and VSS on the t-case or trans if 2wd, or if there is a way to output that signal from the DD setup, do it that way.
 
The DD box does have a speed output slot in it that can either be 2000/4000ppm. I believe the brown wire goes to the A10 slot, would I just wire the brown wire directly into the speed output slot and disregard the original red, green, and black wires? I know the green box also has to do with cruise control and I’m not concerned with retaining it bc I’ll be doing a ls swap in the next few months.
 
Plunkett said:
The DD box does have a speed output slot in it that can either be 2000/4000ppm. I believe the brown wire goes to the A10 slot, would I just wire the brown wire directly into the speed output slot and disregard the original red, green, and black wires? I know the green box also has to do with cruise control and I’m not concerned with retaining it bc I’ll be doing a ls swap in the next few months.
Click to expand...

Correct. The signal originally came from the speedometer via an "eye" for the VSS, then the light green buffer converted it into the signal the ECM needs. Power, ground, and output on one end of the buffer, and the three joined wires should have the eye on the end that was screwed to the back of the stock speedo. If you can output 2000PPM on the brown wire (A10 on the TBI ECM), then should have no problem. IIRC there were some other outputs depending on platform (so just ensure its 2000PPM output on the box), but the trucks were definitely 2000PPM.

That code isn't necessarily hurting anything, but without A10 hooked up, you may notice that there is some issue with how the engine runs when you decelerate. Just mentioning it as I assume that would be something you'd have to change when you went LS anyway.
 
I appreciate your input and I will make the changes to it. I’ve only driven the truck 30 miles since I changed the gauges and with the code 24 popping up the truck wants to die when I let off the gas while going down the road at times.
 
Plunkett said:
I appreciate your input and I will make the changes to it. I’ve only driven the truck 30 miles since I changed the gauges and with the code 24 popping up the truck wants to die when I let off the gas while going down the road at times.
Click to expand...

Yep. You'll hear people say that they have no issues not using VSS with TBI, but if you have issues, that is exactly what they will be.
 
dyeager535 said:
Correct. The signal originally came from the speedometer via an "eye" for the VSS, then the light green buffer converted it into the signal the ECM needs. Power, ground, and output on one end of the buffer, and the three joined wires should have the eye on the end that was screwed to the back of the stock speedo. If you can output 2000PPM on the brown wire (A10 on the TBI ECM), then should have no problem. IIRC there were some other outputs depending on platform (so just ensure its 2000PPM output on the box), but the trucks were definitely 2000PPM.

That code isn't necessarily hurting anything, but without A10 hooked up, you may notice that there is some issue with how the engine runs when you decelerate. Just mentioning it as I assume that would be something you'd have to change when you went LS anyway.
Click to expand...


The signal must be a digital 2000 pulse per mile (or 2 pulse per revolution) to keep the computer happy.

https://jagsthatrun.com/products/speed-sensor-place-holder-4pac

I'll bet your gauge module has a speed signal output, I don't know what the signal pulse is, but it would be worth looking at the instructions as it might be programmable.
 
You must log in or register to reply here.

Latest Posts

Top Bottom