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700r4 w/tbi: What tells the ECM to lock up the converter?

nutt7

nutt7

1/2 ton status
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Location
Ahwatukee, AZ -> JBLM, WA
I got a rebuilt tranny that I installed that won't lock-up. I can apply ground to the tan/black wire from the ecm to the tranny plug and it will indeed lock-up. (the 12v purple wire works correctly with brakes) The blue wire FROM the tranny to the ecm shows ground when in 4th gear, so that works too.

TV cable is adjusted correctly. My ecm is not sending the ground signal to the tranny...why won't it lock up? What does the ecm consider when deciding to engage the converter lock up? Does the tranny have to be a certain temperature? My in pan sensor stayed at like 110* for 30 miles at 75mph. Stayed cool, but never locked up.

The rebuilder of my last tranny must have wired the blue to the tan wire internally, because my 700r4 instantly entered lock up when in OD...that sucked.

I know I can make/buy a controller, but I'd prefer to fix it like stock if possible.

Thanks!
 
I don't know about the tbi, but the signal going to the trans should be 12v (don't quote me on that, it's been a few months) for engagement. It can be interrupted by brake switch, vacuum switch on the motor, stuff like that. I only have a single wire going to my trans. Mine stopped working because the brake switch fried. I bet there is some sort of something that senses load and releases the lockup - eliminating the need for a vacuum switch like I had. I know, I'm a big help :rolleyes:
 
Thanks for trying though :D. The 12v is on all the time (with ignition). The ecm grounds the other side of the solenoid to engage the TCC. Mine has 3 wires...no vac.
 
All I could find is that some say the VSS, CTS, and TPS are all looked at to tell the TCC to lock up. More specifically:

The TCC will engage when:
the vehicle speed is over 30MPH
Coolant temp is above 149 degrees
TPS output steady
Brake switch closed

Can anyone confirm or rebuke this? I just wanna know why my ecm won't ground that solenoid! Tomorrow I will check the output at the ecm instead of at the tranny/ALDL port in the rare case that there is a connection issue.

Any advice is appreciated!
 
Only constant among those I can see, is the brake switch. Is it adjusted properly?

I've got the '91 manuals, I can check about lockup, but I'm not sure if they actually have a diagnosis based on no lockup. It should.

But if you had problems with the TPS, VSS, or CTS you should know...weird throttle problems, cruise won't work, and bad economy, respectively.

Manual states exactly what you said, plus 3rd or 4th gear is necessary.

I'm seeing if my crappy cell phone will take good enough pics to upload the two manual pages that explain it, and the diagnosis flow chart.

PM me your email if you want the pics. I can't upload them anywhere (webshots is gone???) without losing resolution, and they are already poor.
 
Last edited:
nutt7 said:
All I could find is that some say the VSS, CTS, and TPS are all looked at to tell the TCC to lock up. More specifically:

The TCC will engage when:
the vehicle speed is over 30MPH
Coolant temp is above 149 degrees
TPS output steady
Brake switch closed

Can anyone confirm or rebuke this? I just wanna know why my ecm won't ground that solenoid! Tomorrow I will check the output at the ecm instead of at the tranny/ALDL port in the rare case that there is a connection issue.

Any advice is appreciated!
Click to expand...
There is also RPM, depending on the chip/bin/BCC these could all change. Below is a picture of the settings in the chip ASDU which is common on your truck.

Looking at your sig, axle swap and tires, if the DRAC/VSSB was never adjusted your speed could be way off. Check it with a scan tool or if you have a laptop and cable use TunerPro RT.
http://coloradok5.com/forums/showthread.php?t=302680

If speed is not above what is needed then no lock-up. Same if say your gearing is to high for tires, like 3:23 and you have a TPS value greater then tables below to get enough power. I'm guessing speed.

There are also four ground wires to ECM, if one is bad it may be the one needed for the TCC ground. Check wiring diagrams:
http://coloradok5.com/forums/showthread.php?t=302678

TCC-Lockup.jpg
 
dyeager535 said:
Only constant among those I can see, is the brake switch. Is it adjusted properly?
Click to expand...

Yes, it works as it should.

dyeager535 said:
But if you had problems with the TPS, VSS, or CTS you should know...weird throttle problems, cruise won't work, and bad economy, respectively.
Click to expand...

Nothing really, low idle at times and a random CEL here and there (usually ESC code 43 or 32 for EGR)
 
The wiring from the trans case going into the trans solenoids could also be bad not allowing it to lock up or even the solenoid itself bad. There are multiple wiring configurations for lock up also so be sure you're checking the proper schematic when checking it out.
 
eagle mark said:
There is also RPM, depending on the chip/bin/BCC these could all change. Below is a picture of the settings in the chip ASDU which is common on your truck.

Looking at your sig, axle swap and tires, if the DRAC/VSSB was never adjusted your speed could be way off. Check it with a scan tool or if you have a laptop and cable use TunerPro RT.
http://coloradok5.com/forums/showthread.php?t=302680
Click to expand...

I don't believe the 89 has DRAC/VSSB (not even sure what it is). I think that I read that it started in 1990. Is that for ABS or t-case mounted VSS? My speedo is cable driven with that little VSS box behind the cluster.

eagle mark said:
If speed is not above what is needed then no lock-up. Same if say your gearing is to high for tires, like 3:23 and you have a TPS value greater then tables below to get enough power. I'm guessing speed.
Click to expand...

I don't think this is the case. I had 3.73s on 31s from the factory and I have 4.10s on 35s now. That ends up as a 2.7% speedo difference (compared to GPS it really reads 10% low for whatever reason).

I don't have any of that equipment to check the stuff in the chart below, but I can say that on the freeway I am not laying into the throttle too hard. Is there another way to check that?

eagle mark said:
There are also four ground wires to ECM, if one is bad it may be the one needed for the TCC ground. Check wiring diagrams:
http://coloradok5.com/forums/showthread.php?t=302678
Click to expand...

I can check those tomorrow.
 
4X4HIGH said:
The wiring from the trans case going into the trans solenoids could also be bad not allowing it to lock up or even the solenoid itself bad. There are multiple wiring configurations for lock up also so be sure you're checking the proper schematic when checking it out.
Click to expand...

While driving, I grounded connector F on the ALDL (which is what the ECM is supposed to do) and it locked up fine. So the internals are working like they should, unless the 4th gear switch is supposed to NOT show ground when in 4th. (it is open in all other gears and grounds in 4th, verified with DMM)
 
This rebuilt tranny - where did it come from? There were many different internal wiring configurations. I think the TBI ones were some of the simplest ones.

Anyway, there was always a "hot" wire that is hot with IGN on, but broken by the brake switch. So when you say the brake switch works, how did you test it? Normally there are two switches and the one that affects the transmission is not the same one that works the brake lights.

The "lock up" wire is generally about the same as well, but for carb trucks, it comes from the underhood vacuum switch. For TBI, it comes from the ECM. Since you can get lock-up using the ALDL, this must be OK. So that leaves the 3rd wire, which had different ways of indicating "cruise conditions". It was used to enable EGR on some models and give feedback to the ECM on others. If you used a different year transmission, this might be looking for something different?

Is this the stock ECM? When did lock-up last work correctly?
 
I dont think the tranny will kick in lockup with a CEL. And also I think the EGR has a deciding factor in that as well, as its part of determining cruise as well.
 
Blue85 said:
This rebuilt tranny - where did it come from? There were many different internal wiring configurations. I think the TBI ones were some of the simplest ones.
Click to expand...

I bought it from a tranny shop. They did ask for the year of my truck. I don't know what year the trans came from. How can you tell?

Blue85 said:
Anyway, there was always a "hot" wire that is hot with IGN on, but broken by the brake switch. So when you say the brake switch works, how did you test it? Normally there are two switches and the one that affects the transmission is not the same one that works the brake lights.
Click to expand...

My DMM confirms that 12v makes its way to the tranny plug with the key on, and gets interrupted when I tap the brake pedal.

Blue85 said:
So that leaves the 3rd wire, which had different ways of indicating "cruise conditions". It was used to enable EGR on some models and give feedback to the ECM on others. If you used a different year transmission, this might be looking for something different?
Click to expand...

Possibly...as I asked above, how can you tell what year it is? To the best of my abilities, that "high gear wire" (blue) is working as it should. It shows ground when in 4th gear at light or high throttle. It only opens when NOT in 4th gear.

Blue85 said:
Is this the stock ECM? When did lock-up last work correctly?
Click to expand...

This is the stock ECM. I don't know if lock-up ever worked. I bought it with a bad tranny, put in a rebuilt one, but the tranny was wired internally to lock up in 4th AT ALL TIMES. As soon as I hit OD it was like hitting a wall. I read that some rebuilders do this for whatever reason. They take that "high gear switch" and tap it to the ECM ground side of the solenoid's coil. In short, I don't know when it worked last.

454Sub said:
I dont think the tranny will kick in lockup with a CEL. And also I think the EGR has a deciding factor in that as well, as its part of determining cruise as well.
Click to expand...

The CEL isn't always on. Only occasionally, like 1 out of 3 times on a long freeway ride. My 89 manual says that TCC is also affected by a vacuum switch...could that be the EGR?
 
The EGR is controlled by a switch, but its electrical. It is hooked to the TB, and then on the other side it runs a hose to the EGR.
 
So far I know the ECM grounds are good, CTS is good, The VSS appears to be working fine (checked using signal to cruise module), and there is continuity from the tranny plug to the ecm (both wires). Didn't check the TPS but I have no throttle issues at all so I am assuming it works. I need to get a scan! Do places like O'reilly have scan tools so I can see what the computer sees? Or will I have to go to a mechanic? I would consider buying one for the laptop, but I have a mac. I can't fully run diagnostics until I see how everything is meshing.
 
My kid works for Oreilleys but he is the only one who knows how or will do OBDI, so chances are slim? Even if they did have one would they let you take it for a drive and see specs like speed and if TCC is locking up? Most others auto parts are read codes only if you can get them to do OBDI...

Since you never saw TCC work? What is the BCC (BroadCast Code... letters on chip)? ECM is behind glovebox.

Was this a 3/4 ton Suburban from factory?

Just because your CEL is not on does not mean codes are not still stored. It may be why no TCC as well? I just spent an hour looking through code and could not find a specific answer if this is true. Clean codes by disconnecting power to ECM and try again.

HTH! :D
 
eagle mark said:
Since you never saw TCC work? What is the BCC (BroadCast Code... letters on chip)? ECM is behind glovebox.

Was this a 3/4 ton Suburban from factory?

Just because your CEL is not on does not mean codes are not still stored. It may be why no TCC as well? I just spent an hour looking through code and could not find a specific answer if this is true. Clean codes by disconnecting power to ECM and try again.

HTH! :D
Click to expand...

ASDU, iirc. Same serial code that is in your sig. It is a half ton from the factory, and I had the ecm unplugged for a good 30 minutes, and a test drive yielded no lock-up...so it's something else
 
I don't know if it would help you or not but I have a gm factory service manual for the 89 blazer if you want me to send you some pics of the wiring diagrams or anything then pm me your email
 
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