vss code keeps coming up ,but truck

[87_silverado]

hello, let's see if anyone has run into this problem yet. i have a 1987 v10 silverado stepside w/. 305 tbi, the problem is i keep getting a 24 code which is a vss(vehicle speed sensor)about 2 miles down the road. here is where it gets tricky, i have a cable spedometer and there is no sign of a vss sensor on the transfer case or thm 400 transmission.my first guess is wiring to ECM but i do not have any schematics for troubleshooting. has anyone ran into this? any help would be greatly appreciated.

 

[eugene68]

RE: vss code keeps coming up ,but t

just a few things to think about..
what kind of tranny you have? is it an electronic one? could there be a speed sensor hiding inside?
do you have anti-lock brakes??? if so , could they be using the speed sensors located on the inside of the rotor/disk/wheels? that would qualify for a speed sensor since it detects weel speed as part of the anti-lock brake system...
not an expert, just wanted to give you some things to think of..
hope it helps..

 

[87_silverado]

RE: vss code keeps coming up ,but t

>just a few things to think about..
>what kind of tranny you have? is it an electronic one? could
>there be a speed sensor hiding inside?
>do you have anti-lock brakes??? if so , could they be using
>the speed sensors located on the inside of the
>rotor/disk/wheels? that would qualify for a speed sensor
>since it detects weel speed as part of the anti-lock brake
>system...
>not an expert, just wanted to give you some things to think
>of..
>hope it helps..
>
>
first, let me start by thanking you for your reply. the transmission is a thm400 as stated in my post, i looked all over it and there is only one wire connected to what i believe is a reverse pressure switch on the driver's side of the tranny. it is a cable type spedo which is mounted to the transfer case. and it does not have ABS, so naturaly i am a little stumped. i am a detroit diesel and allison transmission by trade, so i am not a mechanical idiot but even i get stumped on vehicles im not used to working on.if you have any other suggestions please feel free to contact me.:7

 

[MarkyB]

RE: vss code keeps coming up ,but t

The VSS should be located on the tailshaft of your tranny, but that may not necessarily be your problem. I would first check to see if the safety-neutral switch is plugged in. If it starts in gear, then that's likely your problem. This unplugged switch can set a false, code 24. If that's ok, clear the code and try running the engine without putting the wheels in motion. If the code pops back up, then check the settings of your throttle postion sensor. If both of those are ok, check the ECM connection, because the VSS sends it's signal to the ECM, where it's converted to MPH. If all of the above is ok, then I would replace the VSS.

 

[87_silverado]

RE: vss code keeps coming up ,but t

thank you for your info but the problem was i could not find the vss. i had already checked the nsbu switch(or the neutral backup if you prefer that terminology). i thank you for your response again,but i found the vss it was in the instrument panel. it has a cable which turns the speedometer which has a blade on it an a module with two leds send a light and it reflects back giving a signal, first one i have seen on a cheverolet. so, if anyone has this problem and cant find the vss look behind the gauge cluster beside the spedo cable.