If an odometer works, does that mean the speedo cable is OK?

2002 Chevy Silverado 2500HD. A co-worker has this truck and her speedometer isn’t working. Her odometer works fine as do all of the other gauges. Am I correct in assuming that this means that the problem is likely within her instrument cluster? She said that as it was starting to go bad, it read about half speed for a while before it quit altogether. She took it to a local service station (he mainly does tires, brakes and whatnot) and he told her that it would be around a $900 repair. I have no idea how he came to this conclusion.

I’ve recommended that she remove the cluster and have it sent to someone that will replace her cluster’s speedometer motor. These services are offered on eBay for about $50 + shipping. Is this good advice for a first step?

If the cluster were to be unrepairable (I can’t think of why it wouldn’t be) and she replaced the whole cluster, is there some programming that a dealer needs to do or is it just plug and play?

Thanks in advance.

When you say “Speedo cable” are you refering to the wiring harness or a mechanical cable?
Speedo’s are driven by pulse generators or magnetic pickups in the transmission on modern vehicles.
Whatever the cause of this problem and i would look at the dash unit also, but a GPS is a good temporary speedo.
I used one in my big truck when the pulse generator failed and when i did my CDL driving license test, the tester flipped out because he said a GPS is a distraction and failed me before we left the curb saying if i don’t pass this test i will have the on board speedo fixed before i retest. I guess he didn’t realize that he was the distraction of all distractions. :dubious:

Huh. I had no idea that they used pulse generators. I just assumed (bad idea, I know) that they used a cable like in the olden days. So what drives the odometer?

It’s probably the instrument cluster and that might not be cheap to fix.

Here is a cheap work-around: buy a cheap GPS unit and use it’s speedo function. Of course it won’t be exactly correct and might not work properly around tall buildings and mountains, but it will be close enough.

I should have put this in the OP but one of the reasons she’s looking at getting it fixed is because people ask her if she wants to sell it. I’d think that a working speedometer would be important to its value.

The odometer works off the same signal going to the speedo.
So yeah if the odo works, then the signal is getting sent up to the instruments,
its just the speedo isn’t working.

As near as I can tell, the speedometer is integral to the instrument cluster and not serviced separately. Repair would consist of replacing the cluster including having the new one programmed to match the vehicle (to set the odometer to actual mileage if nothing else). My estimator indicates this would be in the 500 range at a dealer. I’d ask at a dealer if it can be repaired without replacing the entire cluster at a lesser cost.

The speedo is electronic. There are companies that offer to fix these (google speedometer repair), requiring sending it in as you’ve mentioned. Personally, I’d be leery of going to eBay for something like this.

Here’s a repair video for a 2003 Silverado speedometer:

It may or may not be of any use.

Thanks california jobcase, I saw videos like that but apparently, the 2002 cluster is completely different than the 2003s and up. Nobody seems to want to work on a 2002.

Given adequate signal coverage, GPS is likely to be far more accurate than your speedometer. The two will most likely not match, but it’s typically not the GPS that’s in error.

Yeah, I suspected that the speedo on my 2004 Pathfinder was reading too fast. When I got an iPhone & mounted it on the dash I found I was right, it consistently reads 4 MPH over my actual speed for some reason (don’t have unusual tires). Which means, and I never thought of this until now, that my ***odometer ***is probably reading slightly too high too! Although since it’s always off by a fixed amount not a percentage I don’t know the math to figure out by how much.

I know it would have just made things worse but I’d have torn that jerk a new one. How exactly is a GPS (set to show only speed) any more of a distraction than a factory digital speedometer?!

Ah, but this is a classic case of accuracy versus precision. The GPS is indeed likely to be more accurate averaged over time, but the lack of precision in the instant speed readings could get you in trouble if your local cops are sticklers. Your speedometer, on the other hand, probably isn’t exactly accurate, but it’s very precise. Provided you know what direction it skews, it’s pretty much exact.

One suggestion for the OP is that if you’ve got a smartphone, there’s cheap interfaces that plug into your car’s OBD port and connect via bluetooth to your phone and can display realtime data, including vehicle speed. You could just confirm that the speed sensor is working, or use it as a variation on the “gps on the dash” idea.

I second this. Gauges now days are almost always a stepper motor moving the needle. GM has had a problem with gauge failures; I suspect you’ll find someone who specializes in GM or maybe even Silvarado gauge repair. They just replace the failed motor for the non-working gauge. Depending on where you live, you might even find one locally so the cluster doesn’t have to be shipped off, repaired, and shipped back.