Speed sensor on transmission??

[BigRed80]

Hey guys,

my speedometer is not working and OBD gives me an error code, something about the speed sensor not working. I have already replaced the speed sensor on the rear axle but that didnt fix the problem. Someone told me about another speed sensor thats supposed to be somewhere on the transmission (4r70w, 4x4). Problem is, I cant find the damn thing.

This is the sensor I was told to be looking for but cant find:

All I could find that looked like a sensor is this thing:

Can someone tell me what this sensor is? When searching on Google, this thing comes up as transmission speed sensor, not sure if this is the sensor I am looking for.

And if I am looking for the correct sensor (pic 1), could someone please tell me where I can find it? My mechanic friend and I were just looking at the transmission 15 mins ago and couldnt find it.

Thanks for all the help!

 

[SoHK_alumni]

Your first pic is of an earlier VSS, its a vehicle speed signal generator driven off the output shaft just before the driveshaft. I don't think your 2000 uses one.

The second pic is of one of two transmission shaft speed sensors, used to monitor the internal shaft speeds of the 'box. Allows the PCM to verify the operation of tbe trans. Can be used by the PCM to calculate vehicle speed in many vehicles, but I don't think yours.

On the 2000 Expo, the ABS system uses the rear axle sensor along with an acceleration sensor to calc vehicle speed.

Since you've already replaced the abs sensor at the rear axle, I'd guess the problem is in the wiring, abs module or acceleration module.

 

[BigRed80]

Thanks for that information, SoHK.

Although I already replaced the sensor in the rear axle, I am not sure if the new sensor is really working now correctly. If have heard of a case where there was too much space between the sensor and the gear inside of the differential producing the signal, which ended up looking like the sensor was not working correctly although the sensor was fine. Can this be the case here? Is there any way to check if the sensor is generating the correct signal by measuring the output of the sensor when turning the rear wheels?

Thanks again!

 

[SoHK_alumni]

I think what I would try is to simply plug the old sensor into the harness and zip tie it so it won't hang down and drag.

If your new sensor is not seeing the ring in the diff, you should not see any change at all. If you see any change in error codes or abs problems at all, that would suggest the new sensor is doing its thing.

Other than that, it'll probably take uncommon equipment. One affordable path might be Forscan software on a bluetooth'd laptop and an elm327 bluetooth ODB adaptor. Forscan should be able to watch the ABS system.