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.

1990 K5 Blazer Speedometer Troubleshooting

C

CelBlazer702

Registered Member
Joined
Sep 17, 2025
Posts
13
Reaction score
1
Location
Indiana
I'm wanting to diagnose an intermittently working speedometer on my K5. It works about 20% of the time....the others it's bouncing around from 0, 35, 65, or 85 MPH and staying in place no matter the speed. From what I've researched, it can be traced down to the VSS, DRAC, or the speedometer itself. The odometer works, the trip is stuck on 22 miles, but the tenths still roll over. This is the SM465 transmission, NP241C transfer case, no cruise control. Are there any simple tests to rule out what may or may not be working, or will a scan need to be performed to diagnose? No check engine lights are on.
 
Scan won't pull much, but if you can get winaldl to work, or an obd1 tool that shows live data, you can look and see what the ecm is seeing for speed, as the ECM VSS feed comes off the DRAC.

My expectation is that it's the speedometer itself though, since the odometer still works, if you can measure distance to ensure that it's also not intermittent. If it was the DRAC, VSS, or wiring, then every part of the speedometer would act the same. Three speedo wires IIRC, power, ground, and signal from the DRAC.

I don't know as TBI is "smart" enough to know if the VSS signal is abnormal, bouncing around like that. I doubt it. The ECM would have no clue about the speedometer malfunctioning of course.

Look up kennyw's post with all the manuals, I believe all the computer stuff is in the emissions manual, although there may be a tidbit or two in the actual service manual.
 
I've found a local 1990 G30 Van with the instrument cluster for sale. It appears this has the same speedo...any idea if it is compatible?
 
CelBlazer702 said:
I've found a local 1990 G30 Van with the instrument cluster for sale. It appears this has the same speedo...any idea if it is compatible?
Click to expand...
It's definitely not the same cluster, I don't know if the speedometer itself is the same.
I suspect they made different clusters for different platforms but probably used the same gauges
 
CelBlazer702 said:
Right...I was hoping just the speedometer components would be interchangeable.
Click to expand...

I'd be surprised if the underpinnings weren't the same, but the mounting of the gauge face would likely be.

I'd say it would be worth looking at, especially if you can compare with yours before purchase.

Beware, the gauge needles are quite fragile to get off the post they are pressed onto.
 
CelBlazer702 said:
I'm wanting to diagnose an intermittently working speedometer on my K5. It works about 20% of the time....the others it's bouncing around from 0, 35, 65, or 85 MPH and staying in place no matter the speed. From what I've researched, it can be traced down to the VSS, DRAC, or the speedometer itself. The odometer works, the trip is stuck on 22 miles, but the tenths still roll over. This is the SM465 transmission, NP241C transfer case, no cruise control. Are there any simple tests to rule out what may or may not be working, or will a scan need to be performed to diagnose? No check engine lights are on.
Click to expand...
My 1988 now has 465/241… but started life with a 208 transfer case. Does your 1990 np241 still have a mechanical speedometer?
 
Jumping on here.... I'm having a similar issue but it's the Odometer/Trip that aren't working. I actually bought another complete "working" gauge cluster hoping having "all" the components would end up resolving the issue. Speedometer works fine but the Od/Trip do not not matter what combination i use. So frustrating because I am going to be selling the truck unfortunately after my son and I went through it to make it perfect. Electronic Speedo, checked/swapped fuses, replaced VSS, complete "working gauge cluster so i had another Speedo, circuit board, and rear circuitry. Any thoughts? Only thing i can think of is somehow I've got 2 bad elec motors (Od/Trip gearbox motors).
 
Both the speedometer and odometer are using the same power, ground, and signal to operate, so its got to be something on the speedo circuit board, or the motor as you mentioned. I haven't looked close enough to know for certain, but if one function works, and another doesn't, I have to assume it's two motors.

All you can probably do is look closely at the boards, make sure any contacts present are good, make sure you can't see any obvious failures (as in burned components/traces), and maybe if there is an accessible gear train, see if the teeth all look good, and if it will move with minimal force.

Again, no experience messing with them diagnostics-wise, I wonder if the odometer mechanism can be rendered inoperable if the reset "knob" is damaged or stuck.

Speedometer shops do still exist, it might be worth it if you have one close by, to take one of your speedometers in and see if they have experience and if there is a common issue that can be repaired relatively inexpensively.
 
Trip gears are notoriously prone to failure. The usual suspect is the obsolete hard parts for the trip rollers. If that’s your issue or not, you’d have to put a visual on it to see. I fixed one with three clusters for parts and I’m not even gonna worry about it for the next one.
 
In my issue I ended up separating both circuit boards (bought 2 complete gauge clusters) so that only the "gearbox" motor was connected (The speedo motor sits in a receptacle on the circuit board so can be removed/replaced easy) and then drove around.. no matter what combo I used the "gearbox" motor wouldn't spin..... (but the speedo's both worked perfect in various configs).... so.... (unlikely? solutions) can only be either: bad circuit boards (both, and both look perfect), or bad plugs to circuit board (elec circuitry on both sides of board, possibly the connection to the gearbox motor.... beyond that I'm going to try to check pwr/continuity wherever I can...... All other gauges work perfect, the trip/od just suddenly stopped, my first thought was fuse, the gearbox but both (on closer inspection, dismantling etc appear totally fine, cleaned, reassembled etc). A mystery... lol
 
CelBlazer702 said:
No, it's electronic.
Click to expand...
In your issue i would bet its the gearbox for the trip, and possibly a bad or dirty speedo motor (the motor itself can be easily replaced if can find one (I now have a complete spare instrument cluster and have these components all separated trying to diagnose my issue). I wouldn't think VSS with yours (I replaced mine just to check, so i now have a spare VSS as well). Cheers.
 
You must log in or register to reply here.

Latest Posts

Top Bottom