my speedo wont work until i do 50 or more cruise control wont work until then. changed transmission and no difference dont know what to think to do, any ideas. thanks
THANK YOU VERY MUCH I have been trying to solve this problem since I have had this truck, my Haynes manual does not cover this and again THANK YOU don373There is an output shaft speed sensor on the transmission (if it's a 1997).
There should be two wires from it. pin 1/2 is the o/p of the sensors coil (pulses)which go to the PCM.
On later models (1998 and up);
The vehicle speed signal comes in to the PCM via the VSS (vehicle speed sensor)
that is part of the antilock brake controller.
If it malfunctions, there should be a "P",
but my Haynes manual only lists the check engine flash code "15".
(no vehicle speed sensor signal detected during driving conditions)
but this would only apply to the older type of VSS.
On the antilock brake controller speed signal (mounted in the rear differential housing),
transmits ANALOG speed and rate of deceleration to the antilock brake controller.
(located on the drivers side inner fender).
The antilock brake controller module translates the analog signal into digital data and processes
this information for the dump valves inside the RWAL valve , which modulates the rear wheel
hydraulic brake pressure to avoid rear wheel lockup and possible loss of control.
Ok, back to the rear wheel speed sensor. PCM and vehicle speed indication.
The antilock brake controller takes the the analog pulses from the rear differential exciter ring
(pressed into the differential "carrier" next to the ring gear).
It is magnetic in operation and similar to a pickup coil in an electronic distributor.
The antilock brake controller passes on the digital level speed data to the PCM,
which then sends a signal on the data link to the instrument cluster (CCD) data link/computer
controlled display, controls the tach/speedo and some other functions.
Now, where would we be without sensors and computers and ex-NASA engineers to design
automotive controls for us? Gone are the days of the shade tree mechanic that could fix most
problems with a few tools and some good old fashioned mechanical knowhow.
Now we need computers to tell us what is wrong with our vehicles, and sometimes they
get a bit confused themselves. A standing joke in the place I used to work as an electronic engineer..
"in the old days, it took 5 men to do the job..now it takes a computer and 5 men to do the
The o/p from the PCM to the instrument cluster is via a CCD
(computer controlled display?) twisted pair data link connector.
(they don't make it easy to troubleshoot the instrument cluster..do they?)
From the data muxer to the CCD, it becomes a bit "foggy" to interpret.