Tan/Black wire 16197427 PCM - 1994 Chevy Timing/Tcc?

[kevinvinv]

Hey so I dug up the wiring diagram for my 1994 Chevy 1/2 ton and it says the tan/black wire on the blue connector is the TCC Solenoid control wire.

I traced it out and it has that little connector on it -- which means this is the wire I disconnect when I want to set base timing.

I searched and sure enough the tan/black wire is what is used to disconnect and set base timing... but again- according to my wiring diagram- this is the TCC Lock control wire.

Anyone know anything about this? Are they a shared function or do I need to find a different diagram?

thanks all.

[1project2many]

The TCC wire is tan or tan/black.

The bypass wire to set timing is tan/black.

Never the two shall meet...

[kevinvinv]

Hello sir!!

Thanks! And I'd LOVE to see your diagrams but I cant seem to pull up the attachment. Actually... did you attach an image? In Firefox I done see any attachment and in Safari I see some thumbnails.

Thanks man. If it is too much trouble- I'll find the diagram... apparently the one I have is wrong.

[kevinvinv]

Forget that request... I found what I needed. Just made a dumb mistake and didnt unwrap the tape enough to make sure I was getting the tan/black from the correct connector.

One other thing you might know... do you know if these drivers (like the TCC line) are open drain/open collector type drivers? I am wondering if I can just yank down on them to take control or not. If this is not something you know off the top of your head.. no problem. I havent dug into it yet at all myself.

Thanks very much!

[kevinvinv]

I grabbed the correct wire now and things do seem weird. The voltage on the wire is like 10V instead of the 14 I would expect UNLESS I tap the brake... then it goes up to 14V. Next step is to put a scope on it to see if the 10V is coming from pulsing or is instead an actual DC drop.

Strange stuff.

[1project2many]

Sorry for the delay.

Interesting about the thumbnails. They were links to images hosted right here on Gearhead-efi but somehow I managed to grab the thumbnails instead.

Are you measuring voltage with the vehicle driving or sitting still? When sitting still with the brake applied the ecm is commanded to open the circuit which should cause a meter to show system voltage on that line. The question is why do you see 10v with the brake released. That might depend on whether or not the vehicle is moving.

Folks have been driving the 700R4 circuits to ground for years to manually operate TCC. I don't remember a problem with controlling the 4L60E circuit except that the TCC apply strategy changed from full on/off to a transitioned on / off then finally the TCC in the latest models nover fully locks. I've heard of some guys manually locking these later models but I've never tried it. I *believe* your '94 is old enough that it is on/off but the scope will likely tell the tale.