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I take it this is for the GMC? :huh:
http://www.justanswer.com/gm/4ct9d-1998-gmc-speedometer-not-working-properlywhere-dose-not-work.html
Whoa, slow down my man. Your’re going too far and jumping to conclusions without testing the basics yet. I’d be testing this in car. You aren’t sure if you have a bad sensor and are already about to rip out the cluster. Now you’re trying to go after the PCM. Not the way to do it unless you hate having money.
If you can get ahold of a scan tool that can read live data, scroll to the vehicle speed pid and drive the truck. See if the ECM is getting a reading. If it is, that would point towards a bad instrument cluster and nothing wrong with the speed sensor. If you’re blessed enough to know someone with an oscilloscope you can backprobe the VSS on the signal wire and watch the signal or lack of one on the scope screen.
A quick bit of info for you about the PCM. They get blamed for going out way more often than they do. Very few of them actually do. In the 90’s Chrysler ones would fail more often than the norm of the industry, but to condemn a PCM requires a lot of electrical testing to rule out anything else as the culprit. I heard a guy that handled warranty and rebuilds of a company that dealt with PCM’s say once that of all the ones sent into him, well over 60% of them had absolutely nothing wrong with them. They were misdiagnosed. The expensive PCM replacement did nothing to repair the vehicle. They actual are a lot more reliable than they are credited for, and wrongly replaced by people who either lack the knowledge to properly test it or just tend to throw parts at something in the hope is will work.
i havent done anything yet. the stupid thing went out while driving last night. And i dont know anyone that has a OBD1 scanner let alone one that will give live data. all my friends have done away with their old cars. I like not having car payments and ive put over 5k into my truck the last 5 years so im keeping it forever.
Im pretty sure its the speed sensor in the t-case, but i want to do the diagnostics first since i dont have the money to just vomit parts at it.
so after talking to a bunch of different people and not having the tools necessary to back probe the computer (and not really wanting to tear the dash apart in sub zero temps) I made my brother swap out the VSS in the transfer case since everyone i spoke with said they were the most common parts to fail. I figured he owes me money, HE can crawl around in the ice and snow to do it. 89.00 part though. not too bad as far as repairs go.
its resolved.
step one: acquire sensor from parts store
step two: decide it is too cold to lay in the snow to swap it out, demand little brother who owes you money lay in the snow and swap it for you.
step three: accidentally kick snow at him while he is under there for making you wait over a year for the money he owes you
step four: test to make sure he didnt screw it up
step five: take pity on him shivering and buy him a cup of coffee
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