Vss signal loss issue

alarcont91

alarcont91

Active member
So I already sent my.psom out for a rebuild and got it back yesterday installed it but it still acting up. The rebuild helped. When I'm driving the and come to a stop to 0 mph the vss signal spike up to 30 to 45 mph cause the trans to be in a higher gear when taking off. Was wondering if the is a kit to get around this or if there are wiring diagrams someone has to help me out. I got about a month or so to get it figured out before truck has to go to the dyno for tune finalization and to see what kind of hp/tq it's making. Thanks in advance. I'm going to try and check the ground on the truck to see what going on there and the sensor wiring
 
not sure about the lightning, but i think the path goes from the rear diff, to the rabs module, then speedo, then ecm, sounds like the computer thinks your already moving and sends the trans into the appropriate gear.

not sure why its jumping at idle, have you pulled the vss sensor out and see if there are a bunch of metal shavings stuck to it?
 
do you have rabs? and id you ohm out the wires from the vss to the speedo to see if all is well?
do you have any check engine light? abs light?
that sensor is the only thing that reads speed unless the lightnings are different. so if you have a new sensor, connector is clean, wires are good, you still have rabs, and grounds.......cluster we are assuming is all good since you just got it back........
 
I have led tail light and 3rd brake light. Also my headlight have leds in them but they all have load resistor. Going to see if unhooking those will make a difference
 
Do you notice if the speedo itself jumps? There’s a test port under the hood, Google how to check VSS and you’ll find tons of info on how you can test the signal at different speeds.
 
Raymond_B said:
Do you notice if the speedo itself jumps? There’s a test port under the hood, Google how to check VSS and you’ll find tons of info on how you can test the signal at different speeds.
Click to expand...
Speedo is pretty good now that I got it back from the rebuild place. Some weird is going on when I'm brake that case the signal to jump. Something is say the truck is still moving.
 
Can someone get me a pick of their factory plig wires for the vss and what color is in what position on the plug.
 
There isn't one. It's a Hall-effect sensor, which outputs an A/C signal. Neither wire is grounded - they're discrete circuits to the PSOM & RABS module. But the LG/Bk circuit is considered "Low".
 
Is there a possibility the problem is in the pimpxshift ecm. Because it seems everything in the trucks wiring pertaining to vss circuits is checking out. Or is it possible there an issue with the trans shift solenoids. Ir a malfunction with the mlps
 
Tony, it's not quite as simple as an analogue 0-5 volt sensor. It generates an analog frequency until it hit's the PSOM and then it's a digital frequency from there to the ECM. Like I mentioned there's a test port by the master cylinder where you can check the raw analogue frequency, but you'll need to do it at specific speeds if you're using a multimeter. Steve gave you a wealth if info along with wire colors. Here's a thread where a guy tested his.

Also you never answered my question, does your speedo needle jump at at any time? Does it read zero when Tuner Studio shows zero or when the truck is "dragging"?
 
Needle doesn't jump. Truck speedo and ts speedo show zero at the same time the it spikes to like 40 mph or so and come back to zero. Which makes the truck take off in 3rd gear. As far as I know after spending all day testing wires and ground and circuits with my certified mechanic the problem doesn't seem to be with the truck. We did the 0-30mph and ohm wires. I was also think my the wire were pinned wrong in the connector because I see there was a repair at some point but nothing has changed.
 
Also I am aware of what the wire colors are. But not how they are supposed to be in the connector itself. For example lg/blk on left red/pink on right or vice versa
 
I’ll look for the connector pin out you can gauge the orientation by the shape of the connector. Odd so the datalog shows a jump in speed, but neither speedo needle flickers or jumps? Is that in the datalog attached?
 
The data log show the spike in the vss signal. The needle in the truck stay steady the whole time and the needle in ts speedo hits zero then spike up like the vss signal. I think the problem is in the ecm. But wanted to check wires orientation in the connector to vss to make sure someone didn't pin it wrong on accident when the did they're repair.
 
I also sent out psom to get rebuilt because it was flickering and jump before. But after rebuild it stays steady
 
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