4T65E TCC lock-up issue

[1fatcat]

Girl friends 2000 Grand Prix GT, 3800 w/4T65E, 118,000miles, no trouble codes.

At about 50mph or greater the torque converter clutch will engage and hold on flat, level ground and will stay engaged even on slight inclines. However, if you try to accelerate too much or an incline is too great, it will start to "surge" in and out of lock-up at a pace of about 1/4 second on and 1/4 second off. So it is too slow to be ignition. You can easily tell that this is the lock-up clutch engaging and disengaging. The tach jumps with the surge 100-300rpm depending on the load. If load gets too great, it will down shift as it should. All shift points feel fine and aside from the TCC issue, the trans works perfectly! It has been doing this for about 20,000 miles, we just both know how to avoid making it do it, but it still happens sometimes from inadvertantly pushing it too far. It has not gotten any worse over the last 2 years. The fluid is clean and has always been maintained properly.

Today I put a new pressure control solenoid in it and that firmed up the shifts a bit, but did not fix the lock-up issue. I plan on putting a TCC PWM solenoid in it soon unless someone here has had this issue and can give a bit of advice as to what fixed it?

[Archon]

Had a similar problem with a 2000 Bonneville. What I finally found was a rusted connection where the grounding strap from the battery connects to the floor pan under the seat. Cleaning that up, and getting a good ground solved the problem. I don't know if cleaning the connections will solve it for you, but it's worth a shot.

[1fatcat]

Hmmm, so the main body ground from the battery? This one has the battery under the hood. The car has no types of electrical problems but I will certainly check that before digging back into the trans. It's actually a very nice, clean, well maintained pontiac, so I want to get it fixed to keep it nice. Even though we can drive it fine (more or less) the way it is, I FEEL bad for driving it the way it is.

[Archon]

That car had no electrical issues either, and in many ways I was surprised to find that was the cause. I had done the usual of checking plugs, wires, coils, vacuum, transmission, fuel, etc. With so many things requiring a good solid source of electrical power, I decided to clean up all of the connections. Those from the battery, as well as under the hood. The only problem connection was that ground connection. That was maybe 3 years or so ago, and it's still working fine.

[01bonneSC]

I think its TCC and not electrical at all. The battery ground cleaning stopped my very intermitant hard start, thats it. You are experiencing the very same problem i have, just have learned to drive around it. Trans need to be replaced on mine anyways before i start to mod.

[1fatcat]

Problem solved!
I had no way to reset the Transmission Adaptive Pressure (TAPs) the other day when I replaced the PCS. Today, I got a hold of a tech2 and checked some things out. Here is what I found.

No codes, TAP cells in the 3.00-6.50 range (should be 0.25-1.80). Reset TAPs and went for a drive while watching TCC data. Max values during the test drive:
TCC slip...53rpm
TCC duty cycle...72%
TAP cell learned values...1.23psi
This was all with heavily loaded TCC, thottle down as far as possible without downshifting, so these are perfect numbers. The PCM will only command as much TCC apply as needed to keep the slip speeds low (0-100rpm). The newly learned TAP values indicate that no abnormally high commands were needed to get propper shifts. And BTW, TAP values are supposed to be reset anytime a transmission is replaced or any internal component of the trans is replaced...especialy solenoids.

So, problem solved with new PCS and reset TAPs

[01bonneSC]

Can u PM me how u changed PCS?

[1fatcat]

Well, you have to lower the drivers side of the sub frame and loosen the passengers side a little. I had the use of a lift and a stand crank-jack when I did mine and it still sucks so...

I can tell you this though, the parts were 155 total (w/discount). That was a PCS, an $80 side cover gasket (which is re-useable, but not always) and 5qts ATF. That was all (but oil) dealer purchased with a discount, so you can get the parts cheaper aftermarket. I know napa could get the gasket for like $38 but I needed it that day. The labor time is 5.2hrs, so if there is a shop around you that charges $75/hr, it should cost you about $600-700 depending on parts mark up? Just make sure the shop knows what TAP is and that they have the ability to reset it. Or find a $50/hr shop and pay the dealer afterwards to reset TAPs? Buying your own parts will save you from their mark up too.

[01bonneSC]

Ill do it myself, was just wondering where it was, I thought the PCS was more internal than just what u could get to by removing a cover

[1fatcat]

It is underneath the side cover of the trans. The cover is pretty big and a little challenging to get it out, but there are no springs or gogs that come flying out at you. Everything stays in the trans (except the fluid) when you remove the cover. Then you just locate the PCS and change it. Its one of the front solenoids and looks nothing like the others. It is held in by a clip just below its mounting surface, use a 90degree pick to remove the clip and it will pop right out. But the hard part is lowering the sub frame and engine to get the cover off.

It seperates by the yellow dots...


Edit: You also need to disconnect the steering shaft from the steering rack.

[01bonneSC]

Sweet! thank you!

[bonneville dan-o]

what exactly are/is TAPs?

[1fatcat]

TAPs is Transmission Adaptive Pressure. It is an algorythm that the computer learns and uses to control shift timing by adjusting line pressure. The PCM learns TAPs by monitoring shift times, it watches the engine RPM and trans output speed sensor to identify how long the shift took to mechanically do what it was electronically told to do by looking for the ratio change. If the shift took too long or was too quick, the PCM will increase or decrease the line pressure durring that shift. It will continue to adjust until a certain point (not sure of the numbers).

It is also doing this for set throttle points, so yes, it watches the TPS too. There are TAP cells for this, its like each shift has its own personal pressure for a set throttle percent. Not sure of these numbers either, but I would guess one cell covers about 10% throttle? TAPs are not really learned and set, rather, they are always changing. The first learn is a base, so it can be big if needed, the fallowing learns will be in small incriments. The changes will normally happen in small incriments simply to keep the trans in tune/adjusted as plates and bands wear. So when changing a worn part inside the trans, you need to reset TAPs so the PCM can relearn the values with the new part instead of trying to use the old learned value and slowly changing the TAP too an acceptible level.

In my particular case, is seems as if the TAP values may have been the problem all along and the PCS was not bad? Just seemed weird that the problem was there with the new and old PCS and the TAP reset fixed it? Dont know, just glad to say there has been over 500 miles put on it since and its still shifting perfect, and it used to do it all the time not just once in a while.