Jumping speedomter

[RDPsmoker]

First off I did some searching and couldn't find the exact issue that my 03 has just developed on my last days off, well got worse. I bought the truck with
92k miles on it all stock. It had a random jumping speedometer, as in it would go from cruising speed to 120 then back to speed. It would do this ever every now and then so it really never bothered me. Jump forward to last week and now at 109k miles and it has totally gone bad $hit crazy! As in now it will go from 0 to 120 while sitting still and the weird think is it will only do it while the truck is running.(Driving or sitting still) The truck doesn't do it while sitting with just the key turned on. I changed out the speed sensor and had no luck. Looking for any help in the right direction or some wiring diagrams to help me test wires and further help with diagnosing. :nail: Thanks for any help!!

update for truck
03 6 speed
5" exhaust
tst cr powermax with remote (had issues before this)

 

[chris lang]

The fact it is going from one spot to max or minimum I'd start at a wire grounding to higher or lower voltage. If you could watch it on a scan tool would be ideal.
What I do on intermittent electrical problems is run jumper wires from one connector to the next until you have isolated where it's shorting at. Then find the short, replace the harness, or just run a jumper wire bypassing the damaged section.

 

[RDPsmoker]

That's why I was also seeing if anyone might have the wiring diagrams to help me point to all the different grounds what ground is for what.

 

[chris lang]

03 manual or auto? I'll try to remember when I'm at school tomorrow.
**** never mind. Just saw you posted it.
Also, have you tried taking off the tst?

 

[RDPsmoker]

The tst is going to be taken off to test that when I get back home. Also to mention it will do it with the speed sensor unplugged. I forgot that little detail.

 

[chris lang]

well i tried to upload them but it didnt work. i can email them to you

 

[RDPsmoker]

That would be awesome pm sent

 

[RDPsmoker]

Morning bump for any other ideas!

 

[4x4dually]

It's obvious that the sensor wire seems to be shorting to full voltage. Dropping a gnd would result in no speed shown I would think. It appears to just be a simple magnetic pickup so it just reads the pulses. I would venture to say you have a messed up wire between the sensor and the ECM. Especially since it only does it when the truck is running (shaking.) Worst case is your ECM is biting the dust. Wish I could help but I don't have anything on that year truck schematic wise. The closest thing I have is the diagrams for an '08 5.9. It shows the twisted pair from the speed sensor comes into the ECM on pins C2-44 (Output Speed Sensor Signal) and C2-45 (Speed Sensor Gnd).

 

[RDPsmoker]

Awesome thanks! That's were I was going to start when I get home is the PCM wires. Bump is just maybe have someone that had the same issue :hehe: I'll be home in a week so I should have a report back of the issue I find.