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TCC (Lock up) not locking up on 91 burb 700r4, where to start?

pma4x4

pma4x4

AKA Yankeeroad
Joined
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Apache Junction, Arizona
Full details:

Like it reads, my TCC (torque converter lock-up) is not locking up. I am only a couple months into owning this burban and had suspicion on no lock up i finally got a tach on it and it pretty much confirms that lock up is not working.

The tranny was recently rebuilt thru a shop via the previous owner 2000 miles ago on 5-18-12 I may see if I can stop by the shop and aks for details and tell them no lock up. I do have the receipt and its a very end user generic receipt ""Removed, rebuilt and install 700-r4 transmission. owner complained of 2nd gear slipping"". At this very second I do not know if the TC was replaced or not I am willing to bet

When i took possession the PO stated he never saw better then 11MPG unloaded and it shifted really quick, soft and at very low rpms. I found the TV cable was way mis adjusted. I correct that (vie the TV cable link everyone posts) and shift points and feels were at what felt normal. At this time I felt it was not locking up.

Yesterday I had it at a friends shop for a tranny flush. and he didnt have much time to diagnose the TCC issue. He can get a hold of a scanner that can manually lock up the TCC on command if need be. I decided to have it flushed as when I was setting the TV cable I had set it wrong and after a test drive I could smell warm ATF, that was maybe 60 miles ago. Since then i know have a 29K LPD tranny cooler with a temp gauge on the port out line (going back to tranny).

Next and possibly related issue (unknown)
The brake light has been on for a long time. the PO stated he plugged in his trailer and the light came on and since then it has not come off. My friend was able to pull up a brake code #7 in regards to the EBCM. thats when we ran out of time diagnosing. could this be a problem for the TCC?


This is as far has we have gone on trying to fix the problem. Before I spent hours looking in the wrong place I thought I would post here and see if i can be pointed in the right direction.

1. Is there any way I can temporarly test/bypass/rig the TCC to test lock up myself?

2. Could the code #7 EBCM be casuing an issue with the TCC?

3 as long as the tranny keeps cool enough, in its current state would it be able to do a 1400 mile run and not burn up?
 
TC lockup is directly affected by the brake pedal input, it will never lock up until you address that :D

Also, I would be very worried about that TV cable not being properly set for the last 2000 miles. :(

EDIT: I would not drive it 1400 miles without a lock up and properly set TV cable
 
Brake pedal input yes but I am not sure where the EBCM comes into play in regards to the TCC. I know the brake pedal switch can effect TCC.

I dont know how long or who adjusted the TV cable prior to me purchasing it. its set properly now.

Yeah i was kind of leaning this way for not taking it on the trip but taking our grand cherokee instead.

I did find the details on the tranny receipt. I originally had the wife text me a pic of it as i posted the thread while at work.

The receipts states the following
Customer complained of 2nd gear slipping

shop did the following
Master rebuild kit - 220.00
converter - 145.00
Sun shell - 35.00
pump rotor kit - 38.10
sprag - 55.00
reverse input drum - 65.00
transfer case seal - 15.00

I'm going to stop by the shop that did the work and tell them it lost lock up.
 
Ok ran thru the flow charts in ALLDATA and the DRAC is not sending power on CKT696 which provides power to the H terminal on the diagnostics connection and power on Pin D of the 6 pin connector on the EBCM (brake ECU). Just to be clear I have rear ABS.

This is just in trying to diagnose and repair the brake light switch which is still on

Brake light switch is unplugged as per ALLDATA for testing. I keep getting 0 volts which now leads to the DRAC

Where is the DRAC? and who is it i get a new DRAC from for dip switch programming for tire size?


This is my Turkey day:thumb:
 
Have you checked the fuses? There is one, that may effect more? That powers a seperate brake switch, it's always power on to TCC and applying brake turns off power. It's in the diagrams I uploaded in the Injection Section.
http://coloradok5.com/forums/attachment.php?attachmentid=137532&d=1353550801
Or all diagrams:
http://coloradok5.com/forums/showthread.php?t=302678

You can also lock up TCC at ALDL port by grounding Pin A to Pin F. Here's a picture of ALDL port.
http://coloradok5.com/forums/showthread.php?t=240425

When you get the data logging done it will not only read codes and data but also show switches like TCC, brake etc...

DRAC on a 91 is might not be the white box... it's in the speedo cluster and not as easy to change.
http://67-72chevytrucks.com/vboard/showthread.php?t=313815

But since it has no power and TCC may have no power it may be back to a fuse?
 
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Found the DRAC it was right beneath the radio. 2 mounting screws and it is hanign right there. The DRAC has power going into it but there is for sure no power on circuit 696

as for manully locking it up thru the ALDL. is it really that simple? Is that why the manual lock up kits are just a toggle and some wire?:doah:

I can do this right now and that will tell me if its in the tranny or somewhere else at least!!!
 
Glad I was wrong, mine is there too on a 90, it's way easier to change when you do gears. The pins are no longer available for the speedo DRAC.
 
Well good news. I was able to clear the the EBCM code 7. heres how.

I had the DRAC unplugged for quite a while so no power to anything on that one circuit. I then noticed the brake light was off. I then started plugging items back together that the flow chart had me unplug. one at a time I checked for the brake light. finally got to the EBCM (ABS ECU) and check for power at the pins which was step one of the flow chart and it in fact did have power. I went to go pkug it in and BAM the brake light came on. I unplugged and recheck again. the brake light comes on only when I plug the EBCM in.

I will test drive after dinner but my theory is this.

the ABS gets 2 signals 1) from the VSS via the DRAC and 2)the other from the axle. when the two dont jive the EBCM sends the signal to the solenoids at the ABS proportioning valve to pulse the brakes.

Fact is it looks like if I unplug it from the VSS signal its a self contained system which means I can leave it unplugged yes??

on the same test drive I wll wire up a toggle switch between A and F for the TCC and try that if it does not pop on itself.
 
Last edited:
eagle mark said:
Glad I was wrong, mine is there too on a 90, it's way easier to change when you do gears. The pins are no longer available for the speedo DRAC.
Click to expand...

What do you mean? I have the spot for the DIP switch. 3 of them have wire jumpers on them already from factory it looks like.
 
ok its going to the tranny shop that "rebuilt" this thing on Monday. I may not be the original owner but when it has less then 3000miles and its acting funny then yeah it goes back.

no manual lock up via A to F pins and EBCM unplugged i think made it shift funny. I dunno know on that one.

Well it looks like this one aint making the California trip.:angry1:
 
pma4x4 said:
What do you mean? I have the spot for the DIP switch. 3 of them have wire jumpers on them already from factory it looks like.
Click to expand...
Yes you can solder in jumpers or a DIP switch on the white box type DRAC.

Some other trucks to 91, not yours, have he DRAC is in the Speedo and uses pins from GM. I don't know what to do with them? GM no longer has them. Must be a way to make one?

pma4x4 said:
ok its going to the tranny shop that "rebuilt" this thing on Monday. I may not be the original owner but when it has less then 3000miles and its acting funny then yeah it goes back.

no manual lock up via A to F pins and EBCM unplugged i think made it shift funny. I dunno know on that one.

Well it looks like this one aint making the California trip.:angry1:
Click to expand...
With the TV cable, TCC and a new trans I think going to the shop and not the trip is a good thing.
 
Well, we will just take out Jeep instead. We had a back up plan, its just going to be a tighter fit thats all.

and from what ALLDATA shows in testing and the flow charts and wiring. a bad EBCM will not hinder the TCC.
 
Have you checked that the TCC wiring is plugged in at the trans cas driver side? Also it is known for the TCC solenoid to fail.
 
I am going under it tomorrow and start checking things physically.

As for thew solenoid going out. I would think they would have replaced it in a rebuild. I could be wrong though.
 
pma4x4 said:
I am going under it tomorrow and start checking things physically.

As for thew solenoid going out. I would think they would have replaced it in a rebuild. I could be wrong though.
Click to expand...

The solenoids get reused if they're good.
 
I guess its just me but i figure if your in there mine as well replace the solenoids and pressure switches to but I have been know to be one to cure the patient by cutting the head off too.

Anyways, I got underneath and tested the signal from the jumping the A to F pin for manual TCC lock up. I hooked up a meter to the two wires to lockup the TCC and it received a nice clean 12.8 volts of power each time I flipped the toggle.

So the tranny is receiving the signal to lock up its just no doing it internally so this is as far as I am going to go and will see what the tranny shop says.

I don't know if this helps but I have a 3 wire plug.
 
The TCC lock up changed over the years as to how many wires were used and where they went inside the trans. IIRC my 700R4 is a 1 wire system.
 
If three wire, you have 12 volts to the A terminal through the brake switch, a signal wire coming back through the B terminal and then a computer controled ground going in at the D terminal
 
Yes and that's how I figured the solenoid is not working.

The million dollar question is what signal(s) tells the PCM to send said signal to the TCC?
 
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