4l80e no 4th unless commanded, no codes

[gtstorey]

I did not see any mention of that, maybe I missed it?

Post 96, #3. last little bit "but B reads 0v".

I think the pins may be confused still and pin R was grounded. Maybe.

[travmac79]

Post 96, #3. last little bit "but B reads 0v".

I think the pins may be confused still and pin R was grounded. Maybe.

I have the 4l80e connector pinout in front of me. I grounded pin p. I included that info because I also thought it was odd

[TransGo Robert]

Post 96, #3. last little bit "but B reads 0v".

I think the pins may be confused still and pin R was grounded. Maybe.

Interesting, I completely missed that. Does not make much sense since in M2 and M1 plugged in he was getting voltage but maybe it has a wiring issue as well. Would be best to double check that for sure, all three should have B+ when unplugged.

[gtstorey]

So with transmission unplugged and nothing grounded, what do you get on "B"?

[travmac79]

Could it be the reason that sometimes I have 3 gears, and sometimes 4?

[gtstorey]

If you are grounding P and pulling down "B" to zero, but not "C" to zero it sounds like a wire crossed in the harness. If you ground R does it pull down either of the others to zero?

[travmac79]

Checking things now. Unplugged I get 12v to a b and c

[TransGo Robert]

Checking things now. Unplugged I get 12v to a b and c

Good that makes more sense.

[travmac79]

Grounding r pin, I 12v on b

[travmac79]

Grounding p pin, I get 0v on b

[gtstorey]

Just to make sure I'm clear on "B", that is pin C1-17?

Did grounding R pull "A" or "C" to 0?

[travmac79]

I take that back. Grounding r pin I get0v on b. Sorry about that

[travmac79]

Grounding n pin gives 0v on a.

[travmac79]

Each time I ground a pin, the other two showed 12v. Could my harness connector have loose or burnt pins causing intermittent stuff? It looked like the internal harness connector had been leaking on it for a while when I got the trans.

[gtstorey]

And grounding Pin "P" also gets 0 volts on "B"?

3. With trans unplugged, ignition on, terminal p on the connector grounded, C reads 12ish volts. A also reads 12v, but B reads 0v

[TransGo Robert]

Grounding p pin, I get 0v on b

You must mean 0V on C right?

[gtstorey]

You must mean 0V on C right?

At this point it's completely unclear what has voltage when a transmission pin is grounded. Post 114 makes it sound like everything on the harness and ECM is correct or has an intermittent problem.

[gtstorey]

Each time I ground a pin, the other two showed 12v. Could my harness connector have loose or burnt pins causing intermittent stuff? It looked like the internal harness connector had been leaking on it for a while when I got the trans.

Only you can determine if your conflicting voltage readings you have relayed are caused by how you are measuring or by damaged harness or connector.

[travmac79]

And grounding Pin "P" also gets 0 volts on "B"?

I could have had a bad connection with the multimeter when I measuredit the 1st time. My old multimeter took a dump this week too when I started diagnosing. The new ones ground probe end broke earlier too but the most recent posts, I am sure that everything is correct.

[gtstorey]

I think you need to redo the tests in post #83. Anything that doesn't match that chart needs to be remeasured until you are 100% sure that you have accurate readings. Actually anything that returns a zero/low voltage needs to be confirmed 100%.