Vehicle Speed Sensor

[Cuong Nguyen]

Well the speedo gear is what's connected to the rear side section of t case and it directly attaches to the back of the speedometer. I can only assume for now that the code I am getting for the vss is the revolution sensor on top of the t case.

[Cuong Nguyen]

 

This is what I could find. I cannot seem to find any info for a cable driven speedo.

[Foursightho]

On 1/24/2011 at 10:30 PM, Daves94XE said:

on my 94 it came with 235's and has a red 20 tooth speed sensor gear. i first ordered an 18 tooth to get everything back to stock with 31's. the 18 tooth was too small so(wouldnt contact the t case gear) Rob exchanged it for a white 19 tooth gear and it's dead on. THANKS ROB!you will prob can go with 20, or 19 and be ok but make sure you get the c clip that holds the gear on.

So I have a 95 xe and just swapped to 31's. I have the red gear now. I bought a blue thinking that was correct but its not. Should I get a 19t white one now?

[Mr_Reverse]

Honestly not sure the sensor gear needs to be changed for the small difference in tire size. My 93 came from the factory with 31's and is now wearing 33's. Checking the speedometer using GPS, speed indicator units, and timing distance all would agree with what the speedometer was showing. Now if I changed to different gears, it probably would throw the speedometer off. So either when I had the stock 31's the speedometer was reading high, or the 2" difference when I went to 33" tires just wasn't enough to make a useful difference. 

[Slartibartfast]

Mine came with 31s, and when I ran 235s (snow tires), the speedo read close to 70 when I was going 60. But yeah, I'd check it against GPS to see if it's worth digging into.

[Mr_Reverse]

The VSS in the 87-93 mechanical speedometers is in the speedometer head itself. It is a simple magnet and coil. As the magnet on the driveshaft in the speedometer head spins by the coil, it induces a current that the ECM uses to calculate the speed. It really isn't a separately serviceable part, generally requires replacement if the speedometer head. You might be lucky and just have a wire broken loose at a solder joint or simply unplugged.  

[Slartibartfast]

My '93 just has a reed switch over the speedo magnet. I was surprised to see how low-tech it was.

[adamzan]

My 95 came with 31s and a manual trans, the speedo is only off by 5km/h at 100km/5 on 33s. Not bad, or worth messing with. My 94 SE with 33s was 7km/h off at 100km/h. It was automatic trans, though. The 95 has 4.3 rear end and the 94 had 4.6.

 

My first truck a 95 XE, came with 235s, it was off something crazy like 14 or 17%.

[peejay76]

Sorry, all, gotta bring this thread back to life!

 

Just took my 94 out for a test drive and during the trip the CEL came on, got codes 11 (camshaft position sensor circuit) and 14 (vehicle speed sensor circuit).

 

As for the VSS, the speedometer works fine, but not the "analog" odometer nor the digital trip odometer. As others have stated, the FSM isn't too helpful in troubleshooting or diagnosing this area. Am I looking at a bad cluster? Anybody got tips on what to test? Thanks!

 

***

 

Edit: Errr, sorry about that, please disregard (for now!). Just took it for another spin and now both odometers work. Now, I did reset the trip odometers this time (they were already showing "0.0"), not sure if that made a difference or not, but I shoulda at least tried that the first go-round!

Edited June 21 by peejay76
updated post/no longer need help

[Slartibartfast]

EF&EC-88 of the '94 manual has the correct diagram. All that tells me is that the vehicle speed sensor is wired to the cluster, which is then wired to the computer, so an issue at the cluster would stop signal from reaching the computer. It says nothing about how it's wired inside the cluster, where the issue presumably is, if the speedo works and the odo does not.

 

Annoyingly the description of the sensor (EF&EC-15) is copied from the square-dash manuals, and shows the older arrangement of a reed switch in a mechanical speedo, not an electronic speedo with a sensor in the transfer case. Guess they missed that when they updated from the square dash! Wonder how many people that's tripped up.

 

I did notice the round-dash cluster from my parts car (which I was told had an inop odometer) had cracked solder joints where the little stepper motor for the mechanical odometer was connected up. By the time I noticed this, the parts truck was torn apart far enough that I couldn't test the resoldered cluster, so I can't be certain the cracked joints were the only problem. But yeah, if it acts up again, that's where I'd start looking. IIRC I had to tear it down all the way to the instrument itself to find the fault--it wasn't on the flexy board on the back. Bit fiddly to get the cluster apart, but doable. Be real careful with the clips, especially for the clear part.