I am trying to trouble shoot my blazer and I was wondering if anybody could help me.
About a week ago my blazer started acting up. The speedometer and the tack would go crazy and jump all over the place. Shortly thereafter the ABS light would come on, Then soon I could only get into 1st or 2nd gear. This went on and off for a week. (Now it is dead.) I asked in a newsgroup and it was responded that is was the VSS. I read up on this and the symptoms of that was exctly matched. When we went to replace this we noticed that the dealer, or someone had broken the park neutral switch which the sensors plugs into. So we replaced that right away. But now it is still doing the same thing. My sons friend said something about the ignition switch, but I don't know how that would relate. It really did follow the symtoms to a tee for the VSS.
This is getting to be a real hassle since we now have only one vehicle and we work at totally differnet hours from each other and also on opposite sides of town.
If anybody has a clue to point us in the right direction, I would greatly appreciate it.

Shutternot

 

Speedo usually works off the VSS, electronically in your case.
Tach usually works off the distriburator. Has nothing to do with the VSS. The VSS is a variable speed sensor and is located in the tranny or t-case. No reading from the VSS will give you accurate engine rpms. Tachs work off the distriburator. The distriburator controls engine ignition, and thus the best source for engine rpms.

The truck will go into limp mode so you can get it home or at least off the road, 1st 2nd gear.
ABS is partially controlled by VSS as well.

The ignition switch has a security feature. Is your security light flashing while your trying to start the truck?
What do you mean by it is dead? Does it turn over, does it start and die right away, what exactly does it do and don't do?

Keep posting up and we will get this solved for you.

 

One more thing. If the park neutral switch was in fact broke your truck would not start. It is a safety feature so you cannot start the truck in any gear other then neutral or park. If it was broke, then someone must have jury rigged the wiring so it would start. Then when you "fixed it", and if the jury rigged fix is still there, they may not work together. Thus your dead in the water.

Have you ever got the codes read?
Since the truck is dead your going to have to buy a code scanner, or someone on here can tell you how to pull them by jumping wires. I am sure it is posted, do a search for it.

 

If you can get it to an AutoZone, have them read the codes

If it's stuck at home, you can jump the codes by inserting a paper clip into the top right hand corner of the OBD connector, the last 2 holes on the top row. Count the flashes and consult either a Haynes manual or an AutoZone.

Hanr3 is right, the vehicle speed sensor wouldn't affect your tach. It's distributor controlled. The ignition control module is on top of the distributor and when it starts to go out, it will shut the truck off and won't restart until it's had time to cool off.

 

you cant jump the terminals in an obdII system like you got. you can only do it with obdI. you'll have to use a scantool.

 

You can't jump OBDII?

Well F*ckin A, my bad