I would think a wiring fault, or a short somewhere assuming that it's a fully electronic device. How does the sensor read? If there's a take off wheel or something in the gearbox which drives the sensor that might have disintegrated.. Various bright sparks had the idea of making them from plastic... Which inside a gearbox is a bad idea.
If possible test the harness from the instrument panel to the sensor, via the correct connections to see if the wiring is good. That's really all I can suggest.

 

The speed sensor that drives the speedo on the instrument cluster is a separate sensor from the transmission input & output sensors. The VSS (Vehicle Speed Sensor) is usually located at the rear of the gear near where the drive shafts exit the box.

I've just been advising someone over on the MC Accent section of the forum on how to diagnose the VSS circuit. It's basically the same circuit as the LC Accent (and just about every other Hyundai model too). That thread is at the link below.

Regards.
Scottie.

2008 Accent - speedometer & odometer don't work

 

Thanks for your quick replies. Unfortunately, I'm not in a position to test out the leads on it today, but I did follow instructions I found on another thread here to check the speedometer motor in the instrument cluster. I hooked the white lead from the ignition coil through a diode to the blue lead on the speed sensor and got the speedometer to read when I reved the engine. I would assume that means that the signal line at least is good. When I did that, I checked the blades on the connector to the sensor and they don't appear burnt.

I was reading through the other thread, and I'm thinking that it may be the sleeve assembly that the sensor screws into. I tried pulling that when I replaced the sensor, but was not able to get it out so I just unscrewed the sensor and left the sleeve on the transmission. Is there any good tricks you have for getting that out so I can check it?

 

I hooked the white lead from the ignition coil through a diode to the blue lead on the speed sensor and got the speedometer to read when I reved the engine.

Ah, that sounds like one of my sparky tricks I posted a while back. I'm glad you managed to follow what I was trying to explain to the guy on the other thread. There was a language barrier and I don't think he got it.

Yes, that tells you the signal wire is OK so you just need to check the 12V supply and ground at the VSS. If the supply & ground are good that suggests the sensor itself is faulty. Did you already replace the VSS along with the input & output sensors for the TCM?

I was reading through the other thread, and I'm thinking that it may be the sleeve assembly that the sensor screws into.

Not sure what the sleeve assembly would be? I guess that must be something that's only on the automatic gearbox. We don't see too many auto boxes here in the UK and I've never had to replace the VSS on one before so I can't advise you on that I'm afraid.

 

Yes, I have replaced the VSS and the input and output sensors, so those are no longer suspect; though there is always the slight possibility that I got the faulty one right out of the box. I'll be checking the 12V supply and ground tomorrow. The sleeve is the assembly that holds the gears that interact with the transaxle. It is an automatic. Based on what I have read in o0ther threads and the tests I have already done, I strongly suspect that gear assembly.

You are correct, Autospark, it was one of your suggestions that I followed to test the speedometer (I had to replenish my supply of diodes before I could do that one). I appreciate your input and help on this one.

 

Diodes? You FOUND diodes?!?!

Around here the only place is Radio Shack, and they are slowly depleting their stock...

 

Yeah, Radio Shack arround here is going out of business. They recently closed down the store close by me. I had to order the diodes online.

 

So I got a bit busy over the last few days, but I have finally been able to test the lines in and out of the VSS. They are all reading proper voltage.

 

If the wiring all checks out OK and we assume the sensor is OK since it was replaced, the fault must be with the sensors drive mechanism.
I love it when it turns out to be a mechanical issue. I get to go drink tea while the grease monkeys do the work :wink:

 

Did you ever figure out what was wrong