1985 digital dash issue!!Please help!!
Thread Starter
Instructor
Joined: Sep 2013
Posts: 154
Likes: 1
From: Hamilton Ontario
1985 digital dash issue!!Please help!!
Someone please talk me off the ledge!! I bought this car a couple months ago and for the life of me I cannot get the speedo to work!!
I have had the dash out a couple times. Replaced all the bulbs, checked all the connections. I originally thought it was the vehicle speed sensor on the transmission so after a month of looking for a part that GM discontinued making I finally found one. I had it installed today and,,,same issue,,, the speedo still isn't reading. it is stuck on 0. In the meantime I am using my GPS to read my speed but now its personal.
I need to find out how to resolve this.
On a side note, my odometer is stuck and no longer moves. Also on the trip setting it does not move? somehow they must be connected. I don't really trust the gas guage as it never goes below half(even after putting in a new sending unit a couple weeks ago.
oh ya, my check engine light comes on after being on the highway for a few minutes but I don't feel any difference in the performance. took it to a GM dealer today and they said, sorry, they don't have a scanner t read the codes on a car that old.
any ideas??
I have had the dash out a couple times. Replaced all the bulbs, checked all the connections. I originally thought it was the vehicle speed sensor on the transmission so after a month of looking for a part that GM discontinued making I finally found one. I had it installed today and,,,same issue,,, the speedo still isn't reading. it is stuck on 0. In the meantime I am using my GPS to read my speed but now its personal.
I need to find out how to resolve this. On a side note, my odometer is stuck and no longer moves. Also on the trip setting it does not move? somehow they must be connected. I don't really trust the gas guage as it never goes below half(even after putting in a new sending unit a couple weeks ago.
oh ya, my check engine light comes on after being on the highway for a few minutes but I don't feel any difference in the performance. took it to a GM dealer today and they said, sorry, they don't have a scanner t read the codes on a car that old.
any ideas??
Racer
Joined: Dec 2012
Posts: 347
Likes: 25
From: Rockford Illinois
The odometer probably has a bad motor. Mine had stopped a few years ago, so I bought a used one on ebay for the motor. I just switched them a few weeks ago and it now works fine. The trip setting worked fine on mine when the odometer was not working.
Drifting
Joined: Jan 2007
Posts: 1,908
Likes: 3
From: Supreme Soviet Peace-Loving Pipple's Kollektive of Seattle Wa
I can't believe a G.M. dealer not having a way to read an OBDI trouble code!!!
Locate the ALCL communication connector under the driver's bottom dash knee panel. Use the diagram below to locate the A and B terminals. Use a shaped paper clip or wire strap to connect A and B terminals. Turn ignition key TO ON, BUT NOT START.
The check-engine light will give a short flash, a pause and then two more quick flashes. This is the "12" code, one long and two short flashes that tell you the diagnostic system is operating correctly. It will repeat this "12" code twice more before flashing any stored trouble codes. IF there are NO valid codes stored, it will just repeat the "12" code until the jumper/strap is disconnected.
Locate the ALCL communication connector under the driver's bottom dash knee panel. Use the diagram below to locate the A and B terminals. Use a shaped paper clip or wire strap to connect A and B terminals. Turn ignition key TO ON, BUT NOT START.
The check-engine light will give a short flash, a pause and then two more quick flashes. This is the "12" code, one long and two short flashes that tell you the diagnostic system is operating correctly. It will repeat this "12" code twice more before flashing any stored trouble codes. IF there are NO valid codes stored, it will just repeat the "12" code until the jumper/strap is disconnected.
Last edited by SQUIRMIN VERMIN 84; Sep 11, 2013 at 04:21 AM.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The cluster uses the signal from the VSS to drive the speedometer and the odometer. It also uses the same signal to calculate the fuel economy and range (with a little help from the injector pulse width from the ECM).
One way to test the VSS is to take it out of the transmission and spin it by hand or with a drill motor to see if it registers on the cluster. There could be a problem in the wiring between the VSS and the cluster (either shorted or open). The connector on the VSS could have corroded pins. On your car the VSS is connected directly to the cluster.
If the cluster has a problem then you're stuck. "No user serviceable parts inside". The only way to fix it is to send it to a company that repairs them. That's not 100% true, as you can look at the solder connections between the two PC boards and look for obviously damaged electrolytic capacitors. Generally electrolytic capacitors will either bulge on the end or there will be a "puddle" of electrolyte around them on the PC board. Sometimes you will find a burned part, but that's pretty rare.
One way to test the VSS is to take it out of the transmission and spin it by hand or with a drill motor to see if it registers on the cluster. There could be a problem in the wiring between the VSS and the cluster (either shorted or open). The connector on the VSS could have corroded pins. On your car the VSS is connected directly to the cluster.
If the cluster has a problem then you're stuck. "No user serviceable parts inside". The only way to fix it is to send it to a company that repairs them. That's not 100% true, as you can look at the solder connections between the two PC boards and look for obviously damaged electrolytic capacitors. Generally electrolytic capacitors will either bulge on the end or there will be a "puddle" of electrolyte around them on the PC board. Sometimes you will find a burned part, but that's pretty rare.
Thread Starter
Instructor
Joined: Sep 2013
Posts: 154
Likes: 1
From: Hamilton Ontario
**update** I tested the speed sensor today. (took it out of the tranny and manually spun it with a drill) and low and behold the speedo displayed a reading!
so in my opinion, the digital dash works correctly, the speedo works correctly, the odometer works correctly and the speed sensor works correctly and everything is wired correctly and properly grounded.
I believe I have ruled everything out except the only thing left that I can think of is that the gear(teeth) inside the transmission is my issue?? Anyone have any ideas?
so in my opinion, the digital dash works correctly, the speedo works correctly, the odometer works correctly and the speed sensor works correctly and everything is wired correctly and properly grounded.
I believe I have ruled everything out except the only thing left that I can think of is that the gear(teeth) inside the transmission is my issue?? Anyone have any ideas?
Le Mans Master
Joined: Nov 2006
Posts: 5,032
Likes: 204
From: Greenwood Indiana
2021 C4 of the Year - Modified Finalist
C4 of Year Finalist (appearance mods) 2019
Speedo gears are available on tranny sites like this one, online. 
http://www.performanceautomatic.com/...ter-gears.html
http://www.performanceautomatic.com/...ter-gears.html
Thread Starter
Instructor
Joined: Sep 2013
Posts: 154
Likes: 1
From: Hamilton Ontario
Well, it is official, I have a speedo again! It is what we thought it was. A $2.00 clip that held the gear on that drove the speed sensor gear fell off. 6 hours later and I am back in business! now all 4 bulbs on the dash are out?? I am going back under tomorrow night to check the ground connection as I just replaced the bulbs a couple weeks ago. so I do have all gauges now working. Just cant see them very well
any ideas? I am reading threads and all seems to be pointing to a ground issue. Should I start with the ground on the car? Or the ground on the cluster. I reeeeeeally don't want to pull the dash again
any ideas? I am reading threads and all seems to be pointing to a ground issue. Should I start with the ground on the car? Or the ground on the cluster. I reeeeeeally don't want to pull the dash again
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