No speedometer

[dirtautoguy]

I don’t have much time because the issue made me late for work but I thought I’d put it here toget some ideas.

today I got in my truck like I usually do to go to work and started going down the road. I noticed I was doing about 30 mph but my Speedo said 10mph and then a block later it just said 0. I drove to my dads (he was watching my dogs for me today) and decided it might be better to just trade trucks.

I’m not real familiar with these issues but I know it can mean bad things. So I took my other truck to work.

where would be a good place to start? When I left my dads it seemed to be working again?

 

[PlayingWithTBI]

What year and model (C/K) truck is it?

 

[dirtautoguy]

I guess you might need to know a make and model too whoops!!!

1996 k1500 4l60e

 

[PlayingWithTBI]

1st, I'd look at where the VSS is mounted to ensure it's not coming loose, maybe? Then put a scanner on it to see if your PCM is getting speed signal.

 

[dirtautoguy]

I’ll check it out tonight or in the morning when I have some time.

I have a scan gauge hooked up to it and it has a mph setting on it which should come from the pcm correct?

 

[Joe Dirte]

Cmon nascar n nhra dont use speedos. Just let cops tell ya. They can be ur spotters haha

 

[PlayingWithTBI]

I have a scan gauge hooked up to it and it has a mph setting on it which should come from the pcm correct?

IIRC for 96+ the VSS feeds the PCM which feeds the speedometer. If you loose speed on the scanner then it should be between the VSS and the PCM. If the PCM shows constant speed but your gauge fluctuates, I would think it's between the PCM and your gauge.

 

[dirtautoguy]

Haha that could be pretty entertaining since I work for DOT which is a division of the highway patrol “dear captain....”

Anyway I did a little investigating. I have not crawled under it and checked it out yet but I went for a drive and found the following

0-30 mph= clunky speedo
30 and above still slightly clunky but more accurate

On my scan gauge the mph matched the gauge pretty close however I did notice that the scanner looked a lot like a “lazy” o2 sensor the mph was just as clunky on the scan gauge as the speedo was. This makes me think the sensors on its way out maybe?

my cruise control works properly at all speeds. And it did not bottom out at 0 like it did this morning, I did notice that it did do some kinda odd shifts. Not like it was struggling to shift but more like it shifted at the wrong time especially around 30-45 which I’m guessing was into 3rd gear.

I also noticed if I coasted I had the same result with the speedo and scan gauge, and especially below 30mph. If I hit the brakes and slowed down faster it was more clunky. Once it basically got stuck at 20mph and I was obviously not going 20mph. I forgot to look at the gauge to see what it said at that time

it has done this odd shift a time or two earlier this year but I couldn’t replicate it or pin it down so I left it alone I wonder if they are related?

I haven’t looked at the plug yet but I also realized before this morning the last time it was driven was Thursday of last week and we have gotten a lot of rain lately which if it’s electrical all the moisture I’m thinking could be causing the issue too.

 

[35olds]

I have an 88 silverado , 350 engine , my speedo works sometimes and sometimes does not . Suggetested to me to pull the gage cluster and check the grounds . WHAT grounds ? It is all solid state there with no obvious ground wires . It's been doing this for years , I've replaced parts and have had the trasmission completely rebuilt but nothing has fixed the speedo . I'm not going to spend the money to have my gage cluster repaired , it just isn't worth it . Any clues , thanks , Bob

 

[Fumanchu2.7]

Haha that could be pretty entertaining since I work for DOT which is a division of the highway patrol “dear captain....”

Anyway I did a little investigating. I have not crawled under it and checked it out yet but I went for a drive and found the following

0-30 mph= clunky speedo
30 and above still slightly clunky but more accurate

On my scan gauge the mph matched the gauge pretty close however I did notice that the scanner looked a lot like a “lazy” o2 sensor the mph was just as clunky on the scan gauge as the speedo was. This makes me think the sensors on its way out maybe?

my cruise control works properly at all speeds. And it did not bottom out at 0 like it did this morning, I did notice that it did do some kinda odd shifts. Not like it was struggling to shift but more like it shifted at the wrong time especially around 30-45 which I’m guessing was into 3rd gear.

I also noticed if I coasted I had the same result with the speedo and scan gauge, and especially below 30mph. If I hit the brakes and slowed down faster it was more clunky. Once it basically got stuck at 20mph and I was obviously not going 20mph. I forgot to look at the gauge to see what it said at that time

it has done this odd shift a time or two earlier this year but I couldn’t replicate it or pin it down so I left it alone I wonder if they are related?

I haven’t looked at the plug yet but I also realized before this morning the last time it was driven was Thursday of last week and we have gotten a lot of rain lately which if it’s electrical all the moisture I’m thinking could be causing the issue too.

Check the wires by the transmission harnesses. See if you have any chafed or split wires. Happened To my 96 k1500, I lost speedo, tack and odometer. One of the wires was chafed, it arced, and ground out to the bell housing so the fuse for the gauges in the cab would pop as soon as I tried replacing it