BMX Dad

I swapped out transmissions from one 1995 F-Body into another 1995 F-body last week.

After the swap the speedo did not work and the trans was not shifting properly.

I then swapped the VSS off of the original trans because it worked before the swap and I still have the speedo and shift problem.

With the car in neutral and the ignition on, there appears to be no current in the wires going to the VSS. Is that normal?

What should I test next?

Ricardo

Check the wiring from the VSS to the PCM with an ohmmeter for continuity:

Unplug the VSS.
Unplug the red connector from the PCM
Short the VSS connector terminals
Check for continuity between terminals 31 & 32 on the red PCM connector (lines to VSS)

BMX Dad

I checked the wiring from the VSS to the PCM and there is continuity between terminals 31 & 32. So both wires are good.

I then turned the ignition on and checked if there was any voltage coming out of the yellow wire using a chassis ground and there was no voltage.

What should I check/ do next?

Ricardo

I would scan the car while driving it to see if the PCM is reporting vehicle speed.

bobdec

VSS failures should throw a code 24 or 72, have you seen any ?. When you pulled the VSS connector going into the sensor did you have +5v between the yellow + and purple - wires from the PCM with Ign on. Not sure if chassis ground is a correct check point. If 5 volts is missing could be bad PCM or open circuit in the +5 or - return connector or internal to the PCM.

bobdec

BMX, since you said bad shifting I assume you're talking about the A4 4l60e transmission , the bone stock car in your signature. Any chance the new tranny is missing the 40 tooth reluctor gear in the tail shaft that drives the VSS sensor ? You really need to scan the PCM (previous post by Ricardo) to see if it's sensing speed , to isolate this to VSS, PCM, or speedo . A not so technical test would be to get up to what feels like 20 MPH let off the throttle (TPS%=0) and see if RPM stays 200-300 above the 550 D stock setting. If it does the PCM is sensing speed and keeping engine speed up buy holding the IAC open. This is normal operation, as speed goes to 0 the PCM will close the IAC gradually and put the RPM's back down to 550.

BMX Dad

I did a scan while driving and there is no vehicle speed being recorded/ reported.

Yes it is an auto (I updated my signature). The reluctor gear is there and I swapped the VSS from the original trannny since it worked before the swap. I checked the yellow wire output from the PCM and there is no voltage from that wire when the ignition is on.

Is there a signal (say from the tranny) that tells the PCM to turn on the 5V to the VSS or is supposed to be on when the ignition is turned on?

What should I check next?

I have another PCM from a 1995 3.4L. Is that PCM swap something I can do myself? I was told that I would need to do a PROM swap to make it work.