92 Firebird Automatic

My speedometer went out about 5 months ago. I assumed VSS...and about a week later, it started occasionally throwing VSS codes. I finally replaced it today, and it still does not work. Any suggestions? Could my actual speedometer have went out, and if so is there any way to test it or test to see if there's any signal being sent to it?

The way I've understood from reading that the system on a 92 works is the VSS sends the speed information from the transmission to the ECM which then sends the speed to the speedometer. The odd thing is, my TC has been locking up all this time, which makes me think that my ECM has been seeing some sort of speed information. Then again, I read somewhere on there, about the ECM also determining speed based on sensor values and other readings....but I was never clear on this.

And before someone says it...No, I do not have a speedometer cable. I'm sick of hearing that.

 

Your TC lock-up and speedometer are both controled by the ecm based on the readings from the vss. If the ecm isn't getting info from the vss then your tc won't ulock at the proper speed. If you replaced the vss, then the next place I would look is the wiring from the vss to the ecm.

 

hook a scan tool to it, you can read your speed through it. that will help in your diagnosis.

thanks
anthony

 

My friend has a OTC2000 scan tool, and it'll tell you everything BUT speed.


Any more suggestions?

 

It is probably not the speedo. VSS sender at the trans feeds both the ECM and eventually the speedo. Inspect the plug at the VSS unit on the trans. It might simply be dirty and acting intermittent considering where it's located. If not pull it out and look at the gear. It is plastic and is known to fail. VSS signal as stated controls TCC lock as well as EGR operation. If it runs that way it may eventually default and still lock converter, not really sure on that year.

 

well i have an 89 firebird with a 5-speed and i ripped out my comp convertin to carb from tbi and i need tro know if i can hook it up sumhow without the compt so it works? thanks

 

To know for sure, you'll need to beg, borrow, or steal a scan tool that will show what the computer thinks you're speed is. If the computer see's the correct speed then it the Speedo., if it doesn't it's either the VSS or a wiring problem(and possibly a computer malfunction).


Another note that I might add is that my speedometer was always off, way off. I thought it was the VSS- changed that, then I changed the gears on the VSS and tailshaft(non original trans) for one that the dealer had that was for my gear/wheel combo- not that either. Went to the bone-yard and got a speedo out of a wreck.....bingo. Would have know this from the get go if I had started my quest by getting a scan tool and seeing if the computer knowed what speed I was going.

hope this helps!