AHAHAHAHAH!!! Love it!

 

i believe the mileage and speed is controlled through the abs module because if you disconnect the abs module your odo stops working and the speedo if i remember correct

 

its the abs sensor on the read diff and the output speed sensor on the transmission tailshaft that control the speedometer and (i assume) odometer, i believe the PCM DOES store a mileage also. I say this is controlled by the PCM bc you can buy a programmer (superchips ect) and change the tire size and a few other related things w/ it, but it cannot access the ABS module even to read the codes in it.

 

Well driving with a 5.9 PCM in a 5.2 certainly makes a huge difference. When you floor it you get this super deep sound from the exahust now, and it seems like performance is up a little bit but I didn't drive it enough to be 100% sure. The MPGs didn't change at all, but I'm still getting a low 4MPG so a slight change wouldn't be noticable. I also noticed the rev. limiter sometimes works if you can get it to rev past 5k, usually it will just go up to 5k and just hold there smoothly. But the crazy deep sound you get in high rmps, especially under load, is the biggest diffrence I noticed.

 

unplug your abs module and see the the odo stops ticking

 

iv heard of people pulling the abs fuse to turn off the abs system and still having speedo and odometer recordings

 

The speedometer and odometer both send their signals through the CCD bus so either the PCM or ABS module takes the input from the VSS and translates that to the CCD bus. The cluster then decodes it for the guages and, in my 98 at least, the cluster is the only thing that deals with storing the odometer reading, but I do believe the ABS or PCM sends it's own signal through the bus to tell the odometer to put a mile on it having nothing to do with calculating speed vs. time, just 5000 pulses from the VSS tells the cluster to put another mile on it.

 

yea basically correct, the vss (and the tss) send pulses over the bus, and a computer counts them, based on tire size it knows x pulses = 1 mile, and that y pulses in time z = so many mph.

now to my knowledge you cannot access the abs module w/o the drbIII scantool (which very few shops have, unless they are a dealership shop), and since the handheld programmers can adjust the tire size, i would imagine that it is the main computer (pcm) which is being reprogrammed to count differently when the tire size changes(it might just change the distance associated w/ the set number of pulses, but the idea is the same), this makes me think (i have no proof, except for my logic outlined here) that the PCM is what controls the speedometer, and will update the gauge cluster


my other question then, is if the PCM doesnt story odometer reading, then why do resellers of PCMs ask for mileage along with VIN if they dont need to program it into the PCM??????, no the PCM does not displaly the visual odometer, that is definitely in the cluster, but i still feel that the PCM must store odometer data or else why would the programmers ask for the information???

 

Ah yup, the only reason I threw PCM in there was because the VSS wires also go directly to the PCM, and probably split off into the ABS module too, unless the PCM decodes the VSS into the CCD bus and that's what gets sent to the ABS module.

 

i do believe that the two communicate in some way with each other, and they are both on the same bus, if for no other reason than they both need to be able to illuminate lights on the instrument cluster. i am NOT sure how they communicate or anything like that tho