Beating my head against the wall.. Lb7 vss issue

clrussell

clrussell

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Sep 23, 2013
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Hate to post because it looks bad on my behalf as a tech, throwing pride out the window to get this truck out of my shop..

04 lb7 allison 2wd, previous tow truck..

Problem is : truck came in a couple months back with witing rubbed on the fuel lines, happened to be the twisted pair for the vss or output speed sensor. Repaired with solder less connectors and heat shrink as I do all of my wiring.

Month later truck comes back, same issue as before, only has first and reverse. I pulled the entire trans harness up and checked repaired/ re loomed it all. Put it back together. Same issue.. Checked pins at tcm and tightened a few up that had been wallered by a test light it appeared. Same issue.. Finally got back on the truck today after it sat here two weeks waiting on time.. Put a spare tcm I had on it. Same issue..

I realized today though that in park the speedo will move up to about 10 mph at idle, and oss is about 400-500 on scan tool. When put in drive or reverse it all goes to zero. Drive the truck and it will not shift out of first gear. No codes in tcm, service brake light is on throwing a c0055 vss code.

Am I fighting a trans wiring issue or something in the abs screwing with me and throwing me off?

Just cleaned the abs frame grounds and the connector at the ebcm. About to start looking for other wiring issues after I finish another truck.


Ideas or Input?

Thank you in advance.
 
aklbz

aklbz

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Seems like you've covered a lot of possible issues. Are there any other grounding locations that could be an issue? Nsbu or engine speed sensor, turbine sensor maybe wheel speed sensor? Just some ideas


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clrussell

clrussell

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aklbz said:
Maybe a stuck solenoid...


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Click to expand...

If I clear the code driving itll shift.. Solenoids seem fine in that reguard.. It's just throwing it in limp because vss falls out and tcm won't let it do anything else.
 
x MadMAX DIESEL

x MadMAX DIESEL

<<<< No Horsepower
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Maybe that won't hurt but it's best to twist as close as you can then insert pins into connector. That's a way to shield it, without having actual shielding on it


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Dmax87

Dmax87

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Try a new vss sensor??? Seen a bunch of wiring repair but no sensor mentioned.
 
THEFERMANATOR

THEFERMANATOR

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Anytime you do a repair on them, you should untwist the wires back behind it, I always solder and adhesive lined heat shrink(many years in marine has got me doing this), then I retwist the whole pair back together just to be safe. From your description though, something sounds funky here. You say it shows a speed signal in park, but goes to 0 in gear, are you sure you are monitoring the output speed sensor and not the input? Input should drop to 0 when it goes into gear, but the output should match the driveshaft at all times. Does the speedo work? The ABS gets it's speed signal directly from the ECM. As to how the ECM gets it's signal, it is supposed to get it from the TCM, but I have one diagram that shows the TCM and ECM sharing the same twisted pair with a splice near the underhood fuse panel at least for my 01. Even if you don't have the vehicle speed sensor signal, there is still a good chance the speedo will work as the ECM also reads vehicle speed over the class 2 data bus from the EBCM(this is why those of us with stand-alone swap get the P0500 code when in 4 low. The ECM doesn't get the speed signal from the EBCM to verify the ECM's signal against in 4 low).
 
clrussell

clrussell

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Dmax87 said:
Try a new vss sensor??? Seen a bunch of wiring repair but no sensor mentioned.
Click to expand...

Yes swapped with a known good I have in the shop from my spare allison.

Assuming the turbine speed sensor and output sensor are the same on 2wd. Mine was a 4x4 trans so I put the turbine sensor in it.
 
clrussell

clrussell

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THEFERMANATOR said:
Anytime you do a repair on them, you should untwist the wires back behind it, I always solder and adhesive lined heat shrink(many years in marine has got me doing this), then I retwist the whole pair back together just to be safe. From your description though, something sounds funky here. You say it shows a speed signal in park, but goes to 0 in gear, are you sure you are monitoring the output speed sensor and not the input? Input should drop to 0 when it goes into gear, but the output should match the driveshaft at all times. Does the speedo work? The ABS gets it's speed signal directly from the ECM. As to how the ECM gets it's signal, it is supposed to get it from the TCM, but I have one diagram that shows the TCM and ECM sharing the same twisted pair with a splice near the underhood fuse panel at least for my 01. Even if you don't have the vehicle speed sensor signal, there is still a good chance the speedo will work as the ECM also reads vehicle speed over the class 2 data bus from the EBCM(this is why those of us with stand-alone swap get the P0500 code when in 4 low. The ECM doesn't get the speed signal from the EBCM to verify the ECM's signal against in 4 low).
Click to expand...


Yes shows output speed in park. Actually shows speed on all sensors in park. I had the input and turbine plugs swapped but I got that fixed. In park engine idle input shows idle speed. Turbine shows about the same, output reads 400-500 bouncing around. Soeedo is at about 10-15 mph

In gear not moving the speedo is at 0 and turbine/ output show zero.
 
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clrussell

clrussell

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Can any wire the correct size be used on the speed sensors? Or is it some special wire? Thinking of running a new pair of twisted wires from tcm to oss..
 
DAVe3283

DAVe3283

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In theory any wire should work, just try and stick to the stock gauge wire.

Have you stuck a multimeter on the wires and seen if there are stray AC or DC voltages getting introduced somewhere in the harness? From your photos, I'd be suspicious of cross-talk from the turbine speed sensor. If you unplug the turbine speed sensor (in park), does the output shaft speed go to 0?
 
clrussell

clrussell

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Sep 23, 2013
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DAVe3283 said:
In theory any wire should work, just try and stick to the stock gauge wire.

Have you stuck a multimeter on the wires and seen if there are stray AC or DC voltages getting introduced somewhere in the harness? From your photos, I'd be suspicious of cross-talk from the turbine speed sensor. If you unplug the turbine speed sensor (in park), does the output shaft speed go to 0?
Click to expand...

That's what I'm thinking as well..

I'll try that, didn't think of it.
 
clrussell

clrussell

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Think I found the issue..


I had not been through the wiring between the fuse block and the tcm.. Ended up finding the twisted pairs stiuck together in a puddle of battery acid..

Fixed that and truck runs and drives great again.

I'll report back Monday after the customer drives the truck all weekend..

Thanks guys.
 
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