'90 K5 Speedo not working intermittently

[dlind]

Every once in a while my speedo doesn't work. Sometimes the speedo will get stuck around 35mph and around 65mph. It will randomly start working again.. normally after sitting stopped for a minute or two while in gear (at a light or stop sign). The odd part is the miles KEEP TICKING even when the MPH is sitting at zero. I have never had a problem with cruise control although I can't recall a time where my speedo wasn't working while using cruise.

The vehicle speed sensor looks new and I have never gotten a code 24 (no VSS).. that tells me that the ECM is receiving the vehicle speed signal from the DRAC and ultimately from the VSS. Right?

All the other gauges work fine. I have not taken the dash apart to test the power and ground at the gauge itself yet. I wanted to get some input before pulling the dash (I know, I know its easy but I just don't like doing it)

 

[dyeager535]

The speedometer is sitting at 35 or 65MPH but the vehicle is stopped and idling?

That doesn't seem like a VSS issue, agreed, an ALDL cable to see what the ECM/PCM is seeing at that time would be proof.

 

[dlind]

The speedometer is sitting at 35 or 65MPH but the vehicle is stopped and idling?

That doesn't seem like a VSS issue, agreed, an ALDL cable to see what the ECM/PCM is seeing at that time would be proof.

The speedo will go crazy at any speed and while stopped. Then it will just start working again out of nowhere

ALDL cable is in the mail!

 

[dyeager535]

If you can figure out if cruise is normal while it's acting up before your cable gets there, you'll have your answer.

The signal to the ECM, cruise, and speedo, (ABS maybe?) are all shared. No idea how the VSS codes are triggered. i'd assume your assumption is also correct that it should have tripped one of the codes if the ECM was seeing that fluctuation.

 

[RivMan]

My truck (90 K5) does this exact same thing on occasion. It seems more likely to do it if I park outside on a moist morning, or if it's raining.

I've never really looked into it, but if you find a solution, please post it!

-Rob