dirtracer46

I have a 2000 cherokee 4x4 with 4.0 speedometer jumps from 0 to max when started and continues when traveling. I have clean pcm connectors and cluster connectors and installed dielectric grease.The speed sensor has been replaced.It will even doit whit the speed sensor disconnected.Allso done reset the speedometer goes to 20 first then to 50 then 80 then 100+ then counts down the same.(in reverse).Any Ideas would be apreciated.

captainwoot

You need to have a scan tool that can read live data, check the speed sensor signal. The dealer can get into the cluster and check for problems there, as well they can use their scanner and actuate the speedo. it could be a problem within the cluster itself

dirtracer46

Thanks I have a snap on scanner but have not played with it on this jeep yet will give that a try.I lean toward the display being bad.Will post any findings Thanks agian.

dirtracer46

ran scanner on truck with dash disconnected still shows a reading on scanner.deconnected speed sensor still reads as if truck is traveling but setting still.possible pcm?

captainwoot

Possibly, have you checked the wiring from the speed sensor to the pcm?

upritexj

if you use your scan tool watch your speed reading in the pcm, if its accurate or steady/realistic as compared to speedo the cluster is bad since that info/speed is sent to the cluster via the bus from the pcm. also if cruise functions going down the road that'll tell you that everything is working other than your cluster.

dirtracer46

Should there be voltage and if so is it low like 5volts or less on one wire?I'am going to check and make sure there not making contact somewhere with an ohm meter.

upritexj

i believe a speed sensor makes a low voltage a/c current the pcm uses to make the speed reading someone correct me if i'm wrong. i know i've checked gm front w/b speed sensors to see if there working that way, cause those go bad like always.

dirtracer46

Thank you captainwoot and everyone else I found that the harness going behide the engine was grounded out.On the driver side the back head bolt has a stud for the ground strap and the harness had rubbed through on the white wire with the orange tracer witch goes to the speed sensor.repaired wire and repositioned and it works great.Thanks again!!!!!!!

captainwoot

Good stuff, glad to help!!!

dirtracer46

I really appreciate your help.And I feel that posting my findings may help someone else in time.Thanks agian.I have one other problem with a vacuum leak.But wanted to fix this first.I feel like I can find that if I can get it do it long enough.