Senior Member
Speed sensor(s)
Quick question, I have 2 vehicle speed sensors on the side of my 4l80e trans but only the front is plugged in. I've done some reading and it looks like the 4wd trucks may use a (third?) speed sensor in the transfer case. I don't see a loose pig tail for the rear transmission sensor, is it just serving as a plug? The reason I'm asking is that I'm getting a 72 DTC and wonder if it's a bad sensor or if it's because I have a sensor that's not plugged in.
Thanks
Mike
1994 K2500 Suburban 320,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi (manual front axle lock), Cooling upgrade w/duel 180° t-stats and d-max fan
Senior Member
Shit, my post was lost. On the side of my trans, half way along is the connection for the internal solenoids. On the top of the trans to transfer box, is a sensor, and a sensor on the output housing of the transfer case.
Grant H.
1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
1994 6.5 turbo GMC K2500 4x4 suburban #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, new engine, 0 miles. 3.73 diff, 16 mpg
1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, since 1992.
Senior Member
Grant, thanks for getting back to me, sorry for the delay in reply...
I see what you're talking about with the internal solenoid connector. On the same side there is two (visually identical) connectors, my understanding is that they are both speed sensors.
So I just spoke with the transmission shop and of the two speed sensors on the side of the transmission case just the front is used for input speed the rear is just a dummy (it would be used if the truck was 2wd) and the output speed is measured off a (third) sensor in the transfer case. I've attached a photo but I never know if it works. 4l80e.jpg
Mike
1994 K2500 Suburban 320,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi (manual front axle lock), Cooling upgrade w/duel 180° t-stats and d-max fan
Senior Member
The photo was good, I didn't see the 2 sensors you mentioned, there are view obstructions on mine, but I have just managed to see them, and like yours, only one is used. The sensor on top, which is the extension to the transfer case, seems to be for 4wd H/L position. Your code was indicating a problem with the sensor on the output housing, as it is for vehicle speed and the speedo should have been erratic. After 8 years, I have the suburban running, with the new engine, and ready to road test when the workshop is cleared out, in front of it. That will be after summer, it is to hot to work now.
Last edited by grancito; 09-23-2021 at 03:43 PM.
Grant H.
1995 6.5 turbo GMC K2500 extra cab 4x4 pickup, PMD under bumper, mechanical wastegate, 228,000 miles, rebuilt engine, 4.10 diff, 16 mpg
1994 6.5 turbo GMC K2500 4x4 suburban #9 resistor, PMD in the bumper, mechanical waste gate, 226,000 miles, new engine, 0 miles. 3.73 diff, 16 mpg
1982 4x4 shortbed 6.2 Chev 260,000 miles untouched motor 17 MPG 4.27 diff. Best thing I ever owned, since 1992.
Senior Member
Thanks for the info, Grant. I don't have an erratic speedo, the only indication that I do have, other than the code, is the occasional hesitation or the engine will rev like the trans down shifted. Either of these will occur while driving at a constant speed, mostly around town.
Good to hear you got your engine in. Good luck with the housekeeping and road test.
Mike
1994 K2500 Suburban 320,000 mi., F VIN, 4L80E, 3.73 w/posi., 3" turbo back, no cat, FSD Heat Sync, #9 resistor, SSD heads, SSD intake, fuel miser injectors, Bastard IP (5068), 4x4 posi (manual front axle lock), Cooling upgrade w/duel 180° t-stats and d-max fan
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