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4L80 VSS

bison

bison

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Near Peace River-Alberta
This should maybe have been posted in the tranny section,but traffic seems rather slow there.

Are both in and output speed sensors the same on a 4L80?

This is on a 92 GMC 6.5,2 wh drive.
I rebuild the tranny,now the speedometer wont register on the test drive.It dont set no codes either?
I may have swapped the sensors from their original location,they look the same.
Can they be tested?
Wiring and connectors are tripple checked.
 
I could swear someone told me they were but I'm not positive. I know when mine went bad it coded but the CEL was NOT on. Did you actually scan for codes ? Mine didn't set the light off.
Also is it possible during the R&R you didn't put the reluctor back in ?
 
Same part, can check with a/c volt meter or with scanner when running.

Should be another sensor on the extension housing for the speedo.
 
Resistance should be close to the same +/- 1/2 ohm between the 2 of them, however I don't remember off hand what it is. I can check 1 off the shelf at work but that won't be till Tuesday.
A/C voltage should slowly rise as speed increases from less then a volt to say 5v as with most 2 wire speed sensors.

Found it - - >Resistance 900-2000 Ohms
 

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Tested Ohms on both,1 was 1390,other one 1430.
Swapped sensor locations,speedo worked again,went for test drive,10 mls out on the gravel road to the hardtop the FF'n thing quit again:mad2:.farted with the connectors to no avail:nonod:.Took 1/2 hr to limp home again,thouroughly pissed off:mad2::mad2::mad2:

Still no codes?
 
No codes, huh thats wierd.

Your speedo didn't work at first, but it did shift? When you swapped sensors, speedo worked and it shifted, then went to limp mode, was the speedo still working?

Sounds like the now TISS(previous TOSS) is bad/getting flaky. Are these the old style sensors with the exposed metal on the end, or is it fully covered by plastic(new style). Old style was bad about metal shavings sticking to it, screwing up signals.

Swap it out with one of your other trucks.
 
Speedo worked fine before AT rebuild.
Speedo did'nt work from the get go after bolting the tranny back in,no shift but limp mode.
swapping the VSS sensors produced a working speedo and working tranny for 10 min,then speedo quit again.
Sensors are old style and clean as a whistle. Both Ohm out ok.

Its got to be a connector/wire issue.
 
I tested the VS sensors with the engine running and veh in gear.
The inpout sensor measured 1350+ ohms and from 0 V increasing to 20 V at 1500 eng rpm.
the out put sensor was 1800 OHM and measured from 0 to 10 v at 1500 eng RPM, prob because of input/output shaft rpm diff.

does this sound right?
Jess_sr said:
Resistance should be close to the same +/- 1/2 ohm between the 2 of them, however I don't remember off hand what it is. I can check 1 off the shelf at work but that won't be till Tuesday.
A/C voltage should slowly rise as speed increases from less then a volt to say 5v as with most 2 wire speed sensors.

Found it - - >Resistance 900-2000 Ohms
Click to expand...
 
In 3rd gear they should read the same.

Those sensors have a high failure rate. I'd replace them first before you drive yourself crazy looking for something else. They can be temp sensitive.

Could also back probe it at the speed buffer then drive it.
At least there you test equiment is in the cab rather then running wires under the truck.

After re-reading your last post the resistance isn't close enough for my likeing. Granted it will change with temp however being how there both installed in the trans they should change together.
 
bison said:
I tested the VS sensors with the engine running and veh in gear.
The inpout sensor measured 1350+ ohms and from 0 V increasing to 20 V at 1500 eng rpm.
the out put sensor was 1800 OHM and measured from 0 to 10 v at 1500 eng RPM, prob because of input/output shaft rpm diff.

does this sound right?
Click to expand...

Voltage sounds about right.

Check the female pins on the wiring harness @ the sensor, make sure the little tang that squeezes against the other pin is not flattened out, it should kinda angle across from one side to the other.
 
Have you checked your grounds at the rear of the engine? Maybe one got broke during the trans R&R. When its acting up does the check engine light work, maybe losing ground to TCM and clearing codes. If you lose power to the TCM you will be stuck in second and no codes(most of the time).

Might try bypassing the drac and see if it shifts.
 
Update,
I tested all related wiring back to the ECM and speed buffer.All checked out.
I hooked everything back up and had speedo again.
4 mls down the road the speedo quit again,I crawled under the truck and read the OHM's right there.

Bingo,no reading at the output sensor,dead as a door nail
the critter seems to fail as soon as it reaches OP temps,let it cool down and it works.

I phoned the local supply store for a new one,they want $214 for it,seems a bit steep aint it.:eek:
 
not really,if the input one reads 0,it automaticly cancels the second one,result,no speedo,and limp mode
if the output one reads 0,that one operates the speedo, result,no speedo either,but limp mode.
Thats what i learned today anyway.

yes it baffles me i got no codes, ses light works ,code 12 flashes.

i had 86 and 87 before i rebuild the tranny.
 
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