Just got done putting in a hud system only to find the speedo needle not moving.
Before I take it all apart again any ideas?
everything else including hud works fine.

 

I have just recently helped with some similar issues, but need more info. I need the following info:

Do you have Selective Ride Control? If yes, see if it is throwing a code. This system uses speed input.

Can you see MPH on the HUD?

Can you set the cruise control while driving and see the MPH display on the DIC?

That info can get us going on diagnostics

 

Thanks for responding Dadaroo,

I don't have selective ride control. I'll have to play around with the Cruise.
The hud is showing just fine. The tach and other gauges seem to work just not the speedo.
Wondering if it just needs a good tap to get it unstuck or if I can unplug the cluster which I can feel if I reach up in there. Would that make it reset? I used a kit which came with instructions on making the wiring harness It wasn't hard and I followed it to a t but could it be wrong and be causing the problem? I hate to tear it all down again and not have a plan of attack. any ideas I would appreciate.

 

No need to go into anything without a plan. Here is a little info that addresses your situation. The VSS (Vehicle Speed Sensor) is on the transaxle and generates the signal. The PCM (Power Control Module) takes this signal and sends it to the IPC (Instrument Panel Cluster) 2 ways (2 wires). One is a voltage signal which feeds the speedo, see schematic below. The other is via serial bus (digital) which will show speed for cruise control on the DIC. The FSM does not show how the HUD gets the VSS signal, it just says it comes from the IPC. I think it is via the serial bus (digital).


Since the HUD works, it shows the PCM is getting the VSS signal and feeding it to the IPC. At this time, one of several things are the problem. The speedo motor is broken or the power supply in the IPC is bad. Your tie-in the circuit for the HUD affected the speedo input. Or the PCM is not outputting the analog voltage signal or maybe a bad connector pin, wiring issue.

If the speedo "sweeps" on startup then the internal speedo motor is functioning and therefore speedo is not getting the signal. The sweep signal is done internally and is not feed from the PCM. Should have asked if you get a sweep in my first set of questions.

At this point, need to know:

Can you show cruise speed on DIC?

Does speedo sweep on startup?

Based on the results, be prepared to send me the HUD installation instructions so I can figure out where you tied into. In fact, send them to me anyway I could get some extra info on the HUD. You can email me the info.

 

My guess would be the HUD gets the speed info from the same PWM input circuit that the speedo does. After all, that separate speed signal wire would not be required if the serial bus was providing a continuous speed signal to the IPC.

Did you do any modifications to the IPC, like change the circuit board on the back to get the HUD connector version?

Does the speedo needle sweep when you first turn the key on?

 

I'll have to double check the Sweep I don't think it dose. And I'll check the Cruise tonight.
(at work now)
I did not change any circuits on the cluster this is the original cluster and not a swap out it was working before I added the hud. I did add silver benzel rings which I was careful not to touch the needles, So I don't think anything is a miss there. I'm wondering if I disconnect the hud and see if that affects the speedo which would tell me it is the hud wiring.
Thank for the input, and help I'll try and check these things out tonight.
My instructions I'll have to scan or see if there is a link I can find on them.

 

Lionelhutz, thanks for helping on this. I hope with his installation instructions it can shed light on how/where the HUD gets input. I would think the HUD needs a digital input which could be converted from analog to digital internal to the IPC. The FSM is no help at this level of understanding, written or schematics.

Casamero, don't do/remove anything until we get more info from you on Cruise DIC display, sweep, and instructions. Also, I would like to have Lionelhutz agree to any removal inspections considered for further potential diagnostics.Two heads are better than one. Also please send the instructions to both of us. Thanks, Sam

PS: Lionelhutz worked with me on the previous speedo issues I mentioned and his help was invaluable in getting to the root cause.

 

I believe there is just a connector on the side of the IPC that the HUD plugs into. It should be nothing more than plug and go.

The IPC and HUD are getting a digital signal from the PCM. The signal from the PCM is not analog, it is a pulse train.

Knowing if the speedo sweeps on power-up will help but I suspect it's an issue with the speedo itself. I believe there are some ribbon type cables from the main PC board on the back of the IPC connecting to the rest of the cluster so maybe one of them was knocked loose.

 

Thanks Lionelhutz. Where did you learn about the pulse train? Did I miss that in the FSM or it is Tribal knowledge like a lot of other things? I had heard before that the signal was "digital" from a Forum member. I asked for clarification twice but never got a response. Do all the IPC gauges use the same pulse input? Sam

PS: I did a little more research today and they seemed to indicate that the Plug and Play for the HUD was only for late 1999 and older cars? Interested to know what year he has and what the instructions told him to do.

 

Sam - GM has used pulse trains for driving electronic speedo's since they started putting electronic speedos in vehicles.

 

This is a 2003. It is just plug and play with one wire ribbon connecting to the top rear of the cluster to the actual hud. the only other wires coming out are one plug that looks like a scuzzy port with the main power, the hud display wires and the instrument display wires. I never opened the cluster except the clear front.

 

Ok fired it up and no sweep but the cruise dose show up on the DIC display.
Here is the link for the install that is actually here on forum.
http://forums.corvetteforum.com/c5-t...d-install.html

 

No sweep would make me thing you did something to the speedo when you had it apart. Maybe open it and make sure the needle moves easily by hand.

 

should it move?

 

I agree, you need to remove the IPC to try and see what the issue is. Like Lionelhutz says, If the speedo needle is not stuck, it should move with your finger. Recheck connections and make sure you have no bent pins, etc. Hope that fixes it, if not, the motor or the control board on the IPC may be bad. Keep us updated.

 

Okay I guess I'm breaking it back down.
I'll let you know how it goes Thanks for the input guys.

 

I know it sucks to have to remove it. Remember, just like the rest of us, NO GOOD DEED GOES UNPUNISHED.

 

Ok Dadaroo and lionlhutz I have my speedo back.
Took it all apart just nudged the needle and were back in business.
It's amazing how much faster breaking it down and reassembling it went the second time.
Getting to know my vet inside and out.
Thanks again for your knowledge and help

Casamero

 

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the VSS signal from the PCM to the IPC is a frequency modulated pulse. there's a pullup resistor to B+ in the IPC and the PCM has a transistor circuit to pulse ground to it. the signal is 4000 pulses per mile, which the IPC reads and translates into speed depending on how quickly the pulses arrive. that signal can also calculate the distance the vehicle has traveled for trip meters and odometers (about 1.3ft per pulse)<br />
the reason there are 2 is redundancy. I see serial data communication loss history codes stored in my comptuer all the time, they never seem to hurt anything. if the serial data bus was the only way to send speed info to the IPC I think it would be too vulnerable to failure. this dedicated signal improves the robustness of the critical instruments.

 

Thanks, McGilles, I figure the pulse method also somewhat does the same thing that voltage limiters did in the "old days" to limit needle movement due to voltage changes. What puzzles me is my FSM says the Tach uses a serial bus signal. Go figure?

PS: Do you consider the pulse to be a digital signal? I don't, but it just may be symantics. I think of it as a pulsed analog voltage signal no different that what made the old rotary dial phone systems work by stepping relays at the other end.