So my EBL WUD is showing me that the ECM thinks the 700r4 is in drive no matter what gear I am in. I checked the trans, and the 2 plugs on the driver side (square 4) and VSS plug are both plugged in. Is there something internal that has probably gone bad or broken? I am considering taking it to a shop to have the trans looked at if that may be the case, but do not know if there is a simple solution I that can be DIY.

 

The switch is on the shifter under the console. It has nothing to do with anything inside the transmission, or the wiring to the transmission.

GD

 

Okay, I see the switch there, how do I diagnose what's wrong with it?

The backup lights also are not working when it's in reverse so there is definitely something wrong with the switch.

I'm pretty handy with a multimeter if there is a way to check it with that

 

I would start by making sure the connection is clean and tight. If the neutral switch and the backup lights are both inoperative that would seems to suggest a connection problem with the switch.

Beyond that I would have to consult a diagram. I have not had an issue with mine in that area so I'm not entirely sure of the circuit layout. Do you have a service manual?

GD

 

Not yet, I bought a brand new sealed 88 Firebird manual off eBay a few days ago. Cost a pretty penny $200, but everyone here always refers to me it so should be worth it. Thanks for giving me a tip on what the problem is, I'll wait till the service manual gets here and look though it.

 

https://tpiparts.net/1227165_pinout_diagram

In the upper left of the page, you'll see the Park/Neutral input at terminal B10 at the ECM. If you access the ECM and take a multi-meter from B10 to ground to measure resistance, you should see it change between a few milliohms and open circuit as you shift out of park/neutral into gear. If you don't see this change in resistance as you shift the gear lever, you have some problem with the switch and/or wiring between that switch and the ECM or the switch and ground. I believe the switch is supposed to ground B10 when you go into gear.

 

Thanks so much, I will check it tomorrow!

 

It is the opposite, open input is in drive, grounded input is in P/N. On stick shift cars GM just left the input open, so they are basically in drive all of the time.

msammy, you may find that the tab to move the switch has broken off. So the shifter isn't moving the switch.

RBob.

 

Ah, I stand corrected!