I have a 1994 Firebird that has the 4L60-E Automatic Trasnmission.

On the same day my transmission quit shifting, my speedometer also quit working. All the transmission people tell me I need to re-build my transmission.

I am not buying that the ELECTRONIC transmission that relies on the car speed to shift and the speedometer both going out at the same time being independent problems.

I suspect it is the PCM or the speed sending unit. I do not know exactly how the PCM gets speed information used to shift. Does this input come from the transmission, How can I see if the PCM is getting car speed?

 

...this is probably gonna get locked as this is a board for 3rd gen's.
- anyhow, my money is on the speedo. If the pcm doesn't konw the vehicle speed, it doesn't know where to siganl the trans to shift.

 

It is my understanding that the speedometer itself is just a analog meter displaying what the PCM tells it to, the PCM must get an input from somewhere, (thinking the transmission) and that is the part I need help with.

I need to determine if the PCM is getting the speed input it needs, but do not know how to determine that, not knowing exacly where that input comes from.

 

Try a search or asking on this site:
Drivetrain - CamaroZ28.Com Message Board

 

the VSS went bad. without the speed input from the VSS, the trans won't shift, and the speedo won't read.

P.S. Lots of guys here run 4L60-E's in their cars(like me), so it's still relevant to the forum.

 

Thats what I suspect...The car does not know its speed

Is the VSS a independent sensor? I was trying to figure out where the speed input to the PCM was coming from, I was thinking it came from the tranny (electricly).

Do understand you to be saying the PCM gets it's speed input from a seperate speed sensor? any Idea where this sensor is on a 1994 Firebird? or how to test for it working?

 

Well I got my Transmission going again!

The problem was a short in the wire between the VSS and the PCM. There are 2 wires Purple and Yellow coming from the VSS on the transmission. These should go to pins 29 and 30 on the PCM. I ohmed them out and found the purple one was not making it from the transmission to the PCM. So I ran a new wire from the PCM to the transmission and the transmission now shifts like new and speedometer works as well.

Seems the 4L60-E needs the vehicle speed to the PCM to shift correctly, and that 1 wire was the whole cause.

Before my transmission went out I did not even know I had n electronic transmission or an electronic speedometer. But now I do.

I just wanted to thank everyone that gave me suggestions and helped me track this problem down. THANKS!

 

the "E" on the end of the transmission name stands for "electronic". The 4L60 is hydraulic, 4L60E is electronic.