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

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.

The TCC wire is tan or tan/black.

The bypass wire to set timing is tan/black.

Never the two shall meet...

http://www.gearhead-efi.com/Fuel-Inj...2&d=1331491876

http://www.gearhead-efi.com/Fuel-Inj...21d=1486275824

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.

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!

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.

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.

Thanks for the reply! I actually see that low voltage even when driving super slow ... I was going to look at it in park but when I got home my CEL had come on and I got carried away reading out those codes.... which ended up being Trans code 69 -- TCC ON. So something is definitely going on here.

Mine is a 94. My ECM doesnt have the PWM control wire at all coming out. I am waiting for the Trans shop guy to come off vacation so I can ask him what sort of TCC Control valve is actually in the trans. He calls it a 4L65E which I think typically would have had a PWM setup but... since this is a pretty custom trans, I dont know what they have in there.

My overall problem is that the TCC starts cycling in and out in 4th gear sort of ... on its own. I've modified the cal 6 ways to Sunday to try to precent the ECM from commanding any lockup at all and it still keeps temporarily locking. Tomorrow I should be able to get a scope on it to once and for all confirm that the ECM is not at fault...

We'll see!! :)

Can you disconnect the tan/black wire at the ecm? If the TCC seems to be applying with the ecm disconnected there's a possibility that you have a short or that another component is on the tan/black circuit.

Just a note, 93-95 vehicles were available with either the single or dual TCC control solenoid circuits. Good idea to check with your builder.

Does the TCC behave the same way in 3rd gear?

Third gear is not exactly the same... it is MUCH less of an issue in third but it still does seem to engage there when it shouldn't.

What do you mean by dual TCC control solenoid circuits? Do you mean the PWM controller?

One thing you might also know is -- I note in TunerPro there is a TCC Feedback bit in the stream. I presume that somehow this signal is part of the code 69 that I am now getting... (TCC Stuck On). Do you have any idea where this feedback signal comes from? Still doing some research on that but thought I'd ask since you are so helpful :)

I'll try a disconnect after I see what the scope says tonight or tomorrow. This is getting interesting.

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What do you mean by dual TCC control solenoid circuits? Do you mean the PWM controller?

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The second generation of TCC control involved two solenoids. One to apply the solenoid and one to bleed off pressure as the TCC applied. It was an attempt to smooth clutch application.

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One thing you might also know is -- I note in TunerPro there is a TCC Feedback bit in the stream. I presume that somehow this signal is part of the code 69 that I am now getting... (TCC Stuck On). Do you have any idea where this feedback signal comes from? Still doing some research on that but thought I'd ask since you are so helpful :)

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Unfortunately I do not. Sorry...

Today I scoped the tan/black wire on the way to work. Very wild observations.

When engine was cold, the line was at 12V solid.
5 minutes into my drive it began pulsing (all the way to 0) at maybe a 80% duty cycle... meaning, engage TCC for 80% of the time
This happens EVEN when at low speeds and EVEN in PARK
Pulsing stops when on the brakes

20 minutes into the drive as the pulsing continued unchanged, the TCC started fluttering... which is the problem I am trying to solve here
Touching the brakes unlocks the TCC fully as you might expect

I pulled over and cut the gray and tan wire leaving both sides open

No more fluttering
The voltage coming back from the tran on this wire was a solid 12V (B+)

I carefully reached over and grounded the wire, the TCC locked firm like you would expect

Conclusion so far:
for SOME REASON , my ECM is pulsing the TCC lockup wire... Time to swap back to a factory original PROM and see if this happens there.

SO far I am happy that the issue seems to not be in the trans!

Well... I'd say swap ecm. There are usually enough variables preventing lockup at low speed that I would not expect you could accidentally engage tcc like this. Especially if it is happening with the brake applied.

Already swapped ECM... no difference :)

It does NOT pulse when the brake is applied... so that is at least "normal"

I am beginning to wonder if somehow the ECM is trying to PWM the TCC... it should not be doing that... all the PWM stuff is shut off in the bin... but I dont know...

Thanks for your help! :)

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Originally Posted by kevinvinv

I am beginning to wonder if somehow the ECM is trying to PWM the TCC... it should not be doing that... all the PWM stuff is shut off in the bin... but I dont know...

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One bit of advise, one very knowledgeable transmission person cautioned me that some definition files have mistakes. A lot if this stuff is reverse engineered with a big fat guess. So what you think you are changing might not be what the computer sees or likes. I tried a few pretty wild trans changes pushed by "experts" on the forum then when the trans started doing some weird stuff, I went back to factory programming with just the minimal changes I needed. The results were a lot better.

I will also suggest that it's possible the code itself has an error. If the mask ID is set to $AA or if the checksum was recalculated with an incorrect bit there will be little way to confirm without a bit-by-bit comparison with a stock file.