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Discussion Starter #1
Hey all, i somewhat recently bought a 2000 k3500 4x4 base with a plow. It’s got the 7.4l and the 4l80e.

I started to experience 1-2 hard shifts. The speedo wouldn’t start to rise until over 10mph.

I did a lot of reading and found that the TPS can cause issues with 1-2 shifting. Replaced it and that seemed to help some. (I also cleaned the super nasty throttle body).

So after reading (and looking at the transmission) more I found that there is a VSS sensor on the side of the trans and one on the tail end of the trans. (They are different styles) The one on the tail end of the trans apparently feeds the speed info. I replaced that sensor and found that the speedo stopped working completely. But it does seem to shift ok. I checked the rear VSS plug with a multi meter and with the key on it gets 4.72 volts. I wiggled the plug end and did not see any voltage issues.

I replaced the new VSS (that I just put in) with the old VSS to test, and have the same results, no speedo.

Any ideas on what to check next?

I will replace the VSS on the side of the transmission soon.


Prior to all of this, the speedo would work fine between 10 and 50, anything over 50 and it would randomly jump around, most of the time. The cruise worked some, but not great. I also stated to notice it shifting in and out of overdrive at highway speeds, randomly.

I do have a new 1-2 solenoid and the TCC solenoid to replace (i will do a pan drop, filter, gasket and fluid fill).


Fluid level is good.

Thanks in advance!


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The VSS sensor on the front of the transmission is the input shaft speed sensor and the one at the rear is you output shaft speed sensor. Most 4x4's don't have the rear one on the transmission because they will use the one mounted on the tailshaft of the transfer case. I have heard of vehicles having all 3 though.

The sensor that runs your speedometer should be the one on the transfer case. Remember even with a good sensor if the wiring is bad then it still doesn't work. You should have a dark green wire and a dark green wire with a white tracer going to the sensor on the transfer case, there is most likely a secondary harness right where the transfer case and transmission connect and the wires may change color...

Either way those wires will connect to your PCM under the hood in the black connector at pins 3 and 4. Make sure you have good contact and continuity from there to the sensor.

I would also pull the sensor and make sure that it is clean and then look into the hole and make sure the reluctor wheel is clean.

If the vehicle is shifting properly though then the above may not be needed.

It could also be a bad cluster, or bad wiring to the cluster.

I would highly recommend getting a cheap scanner that can produce live data. They have several apps that can use your cell phone and a cheap adapter for less than $20
 

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Discussion Starter #3 (Edited)
I have just tested with my cheap scanner. Vehicle doesn't output any speed. This is a problem for sure.

I am guessing the harness is bad at this point as that was the only thing I moved aside putting in the new transfercase (rear) VSS.

My truck only has 2 VSS sensors, 1 on the tranny and one on the tailshaft/transfercase.

As I stated, I did move that plug a big to get it unplugged and replugged in. The end looks good. I did test the rear VSS/tcase harness plug and with the ignition on it shows 4.72 volts.

I put the old VSS sensor back in and have the same results, so I know it's not the VSS sensor on the TCASE.
 

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Discussion Starter #4
I also tested the plug that goes into the rear VSS, 4.72volts solid when the key is on, 0 when it's off. If I switch polarities I get -4.72 volts, so yes that wiring should be good. I wiggle it too and noted no drops, solid 4.72 volts.
 

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Discussion Starter #5
So tested again, now it won't shift out of 1st gear. No speedo either.

Taking it in next tuesday to have them look at it, hook it up to a scanner. This truck is really starting to piss me off.
 

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Discussion Starter #6
Starting to wonder if both sensors are bad. The old and the new. Anyone know what ohms they should read out at?


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Discussion Starter #7
Truck will sometimes go into a default mode and shift fine at 1500 rpms, which is obviously not right. Speedo still dead.

Maybe the wire harness to the 4l80e or the entire wire harness is shot.

It's going into the shop tomorrow as I'm sick of laying on the ground fighting this. We have a bunch of snow coming and I'll need it working.
 

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T case is hit. It’s the rear right sensor in that that controls speedo.

Covered in metal or mud?

Without the metal, the magnet can’t pick up the worn out speed ring.
 

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Discussion Starter #10
No, sensor is brand new.

I have had the local shop (reputable) take a look at it. They have diagnosed a bad PCM. I have a new one on order.

I had to of course supply the VIN. I will have to do the security/antitheft relearn (which they provide instructions) and then take it back in to get the crank relearn code removed.

Hope this fixes the issue. I know the transmission isn't shot. Lead to the rear VSS is getting power too.
 

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I hate to say it, but I doubt this will fix the problem, I have rarely seen a PCM go bad, but the pins and wiring are not uncommon. I hope I am wrong though.

To the best of my knowledge the VSS isn't a device you can ohm out and check. It is a signal generator.

It's a shame, I have 2 of the blackbox PCM's sitting in my garage that had 1999 4wd 454 engines, 4l80e tranny. I would have sent you one for the cost of shipping. I swapped them out for the 0411 PCM when I converted to Coil Near Plug ignition. The other one came with an extra motor I bought.
 

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Discussion Starter #12
If this doesn’t fix it I’m going to be SUPER pissed. I hope you are wrong and the shop i trust is right.

Damn! Wish I would have known that, I could have saved some cash.


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Did you try draining the t-case fluid first?

He’s right about 5v.
 

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Discussion Starter #14
I would need to look up the fluid to refill. The truck shifts in and out of 4wd fine.


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Discussion Starter #15
Replaced the ECM, did the security bypass, and still no speedo WTF!


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Replaced the ECM, did the security bypass, and still no speedo WTF!


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There’s no speed ring left in the Transfer case
 

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Discussion Starter #17
I stuck my finger in there and I felt it... i assume that means it’s in there. Felt the teeth and all.


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Discussion Starter #18
So just to recap, my speedo was acting funny, transmission started to shift firm on 1-2. I replaced the rear VSS (on transfer case) and lost my speedo. I have checked the voltage at the plug its 4.72 with the key on. I did swap back in the old sensor, same result. I have to imagine that harness has an issue, wouldn't you agree??
 

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Discussion Starter #19
P.s. shop ohmed out all wires for VSS ect.


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Discussion Starter #20
So after having them check it again, they found the VSS sensor tab was tweaked just a bit.... (my fault) I swear i slid it in nice and then tightened the bolt up nicely.... The bent tab caused the sensor to be off just enough. The old sensor I know I mangled getting out.

Speedo works, ABS light is gone and it shifts and drives good. ABS is acting up a bit now though without a ABS light on....

So back to driving but I have to figure out what is causing the ABS to engage when it shouldn't.
 
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