intermittent not shifting out of first gear

Hi,

It honestly sounds like an issue with the VSS. I attached a pic below just to confirm it is the sensor you replaced.

Can you tell me if there are any diagnostic trouble codes?

I attached a pic below showing the wiring to the PCM from the VSS. Check to make sure nothing is loose, specifically with the light green wire. Since it doesn't happen all the time and you are able to do it by driving slow, I have a feeling it is a connection issue.

Let me know if there are codes present.

Joe

Yes, on 4 wheel drive it's on left rear of transfer case. I am certain i have replaced the VSS. No codes whatsoever. Not sure i understand why a connection problem and driving slow would create the problem. I have a Haynes manual and diagram clearly shows the VSS wired to the TCM and tcm connects to the main computer (whatever it's called), and computer drives the speedometer. Just seems the TCM is in between and may be the issue. Sure wish i could buy one, try it and return if not the issue. :) more thoughts? I have also unplugged and inspected the connectors on the TCM, VSS of course and the 2 on the main computer. Look clean and good.
I also swapped the ignition switch after reading about possible voltage or signal issues.

Just tested the wiring from VSS (jumped the 2 wires together at the VSS plug) and tested at the TCM plug pins. Just reading the very low resistance of the wires, plus moved wires around and no change to readings. Pretty certain wiring is okay from VSS to TCM. Light green/black and purple/white. Hope to see any other thoughts from you. Thanks.

See my multiple updates. I swapped the TCM to no avail. So, VSS on xfer case, ignition switch, TCM have been swapped and the wires from VSS to TCM are verified. I am completely baffled....

Hi,

I just went through your replies. You've done a lot. Since the speedometer stops when the problem occurs, I'm starting to question if it is a solder joint or something intermittent in the PCM. I am going to get the advice of the site owner. Hang in there. We'll get it figured out one way or another.

If you see a reply from Ken, he is the owner. Lets see what he thinks.

Take care,
Joe

Thanks Joe. sorry for late reply, i was having problems accessing your site. Basically, i can sometimes recreate issue by letting the truck move very slowly, like less than 4 mph, and when i then accelerate out, sticks in 1st and speedometer does not work. Also i found that when it is happening, i can manually shift to second gear, try 3rd and revs up like neutral, not sure if neutral or if it's going back to 1st. I have to stop truck completely to get it to work and start shifting again. This works every time when problem happens. Joe

If I can add I have seen the instrument cluster cause this issue. here is a video to help you fix the problem. We should scan the CAN as well.

https://youtu.be/_HEC44xENxw

and

https://youtu.be/InIlnsjOVFA

Please let us know what happens.

Shop found no codes in CAN system. They don't think it's in the inst cluster. The are asking me to take it to a transmission shop and check for a bad reluctance wheel in the xfer case. They also replaced the VSS with Ac Delco brand to no avail. Thoughts? This is nuts, sounds like another guess, not sure chances of a passive reluctance wheel/gear going bad.

If i swap the inst cluster myself, what happens with the current mileage odometer? Heard it's stored in the cluster..

You wouldn't be able to just swap the cluster, GM has part of the security system in it and swapping it out requires it be programmed to the vehicle.
With the speed dropping out when you go slower I say it sounds more like a low signal voltage into the TCM causing a problem. A bad reluctor wheel could do that if it moved on the output shaft but I'm not sure how it would as it is between the oil pump and a retainer ring. Easy enough to check though. Remove the VSS and look into the hole it mounts in with a mirror or camera and rotate the rear drive shaft to move the wheel. It should be centered in the opening and solid with no cracks or breaks. The teeth should be evenly spaced and clean. There is a TSB on these for the connector for the VSS getting loose or broken. Loose pins could cause a drop in signal level but you would need to use an oscilloscope to see the signal in real time to see if it was that. For that you go to the TCM and tap the signal, then run it and see if the signal is dropping out from the sensor or if the signal is OK but the TCM has an issue. You might be able to do that test with a VOM set to read very low AC voltage. You want to see the voltage drop off evenly until the truck stops. If you started with say 1 volt and as the driveshaft slows down the voltage abruptly goes away but the shaft is still turning then you know the problem is sensor,connector or wiring related. As you tested the wires they should be okay, the replacement sensor should be but ?? with parts these days. If however the voltage starts showing as soon as the shaft starts moving and increases with speed and drops off the same way, the issue is in the TCM or ECM signal processing.

The reluctance wheel is for sure not centered on the VSS hole. At best the sensor metal nipple is looking at the edge of the gear/wheel. Not sure how or why that has moved. I will try to get a pic.

Here is a picture:

That could be enough to cause a low signal. Perhaps see if you can move it over and see if it's loose or shifting on the shaft. It shouldn't move unless one of the clips failed.

Nope can't move it. Pass it on, and i'm going to have the transmission shop focus on that, xfer case has to come out anyway, got a leaky input shaft seal on it.

They should be able to take care of it then. Once you are sure it is or isn't the reason for a poor signal you would have an easier time testing. Or test it now so you have a base value, that way you could test it after the repairs and see if it improved.