2004 Peterbilt 387 Speedometer Died

That would be your output speed sensor. Unplug the sensor and on the pins( not the connector but pins on trans) test for resistance. Example sensor spec = 2k ohms at 20 degrees C. Reason for the temperature is because a resistance increases with heat.

In a nut shell you speedometer isnt getting its signal. If sensor is good probably the wiring and very unlikly the speedometer has failed. That has a resistance specification too.

 

Just the Guy I need to ask. Would anything besides speedo/ odometer itself cause my odometer not to work. They both quit along with cruise. Changed one sensor fixed speedo, other one fixed cruise. Still no odometer. I’m guessing I need new speedo/ Odom. Anything , aside from a broken wire somewhere? 2000 Classic 12.7 w/ 13 spd. Thanks

 

I think your all over it.

I agree a new speedo head is in order. If the speedo works so should the ODO.

 

any update

 

happy birthday

 

I can't see the tone ring in mine . You must have a different transmission in yours. Mines a 07 387. And the speedo just bounces around and cruise comes on and shuts off rite away . Did you find the problem

 

My cruise and speedometer don't work, just bounce around. I changed speedometer head / speed sensor still same problem and cruise comes on the shuts off right away. I'm thinking broken wires or a bad ground. Now the dam Jake brake works when it wants to . Ugh

 

I’ll update. I changed the speedometer and now the new odometer works. Ametek brand. Same as original. New face doesn’t match, and OD is digital. New one has dip switches set the same as old. Old one always showed 3 mph faster than actual speed. New one shows 3 mph slower than actual speed. Need to fine tune the dip switches. Otherwise I’m happy with the new one. Old style is obsolete.

 

Is the trans output yoke loose? Rust around the nut/washer? If so, the tone ring can spin and drop signal. Remove the sensor and see if you can move the tome ring with a pocket screwdriver.

Otherwise suspect wiring issue from VSS to engine ECM.

Can you connect to the ECM and monitor the vehicle speed when it drops? Then you will have a direction to look.