Lock up coming on and off with engine light

[n01tk]

The lockup torque conv in my 2001 VW TDI 1.8 is not functioning properly. Problem seems to appear after installing a new torque converter ( although my wife says she noticed slip going up a hill when on hyway before tc change out?) code 740. The orginal TC was changed due to flywheel damage. Transmission shop thought new TC ( rebuild) was problem so they ordered another and installed. Still same problem. Next fix was the valve body. Bored out port related to lockup and installed a oversize valve. Same problem. The code reads torque converter lockup " open circuit" so the wiring harness was changed. No diferrence? Now all that's left is the two conductors to the computer and the computer itself. Any other ideas ?

[CoolAirVw]

might have wrong converter. There is one with a bushing in teh stator and one with a bearing in the converter. Mismatch it one way and it wont go in. Mismatch it the other way and you get a TCC code.

Your code definition is off. P0740 means TCC slip NOT " torque converter lockup open circuit". There is a big difference in the diagnostic process between a solenoid "open circuit" code and a TCC slip code. The meaning of the two codes is extemely different. Some OBDII definitions are "screwy" and could lead to misdiagnosis like trying a harness when its not an electrical issue.

If you drive the car with vag-com hooked up you can watch and graph TCC slip. This wont tell you what is causing it, just that its slipping which you know allready since you have the code.

[n01tk]

I spoke to the transmission tech and he says it's TCC open circuit come up when the engine light comes on. The lock up appears to work properly for days and than the engine light comes on and no lock up. What's strange is, with the engine light off ,I turn the car off and than back on again and the engine light will come on ( not always ). Seems to come on when starting more so than actually driving ( why would it be calling for lock up on starting). This may be a startup routine to check the TC LOCK UP circuit continuity but why would it change so quickly ( circuit appears OK just before shutting down, but light comes on when started immediately)? Any ideas.

[CoolAirVw]

The lock up appears to work properly for days and than the engine light comes on and no lock up. .

The code usually means the computer notices a slip despite how OBDII defines it. If your guy was scanning with vag-com you would get a better code definition. Once the code triggers the computer will no longer command lock up on. It takes certain driving circumstances, a certain number of times for the computer to trigger the code.

What's strange is, with the engine light off ,I turn the car off and than back on again and the engine light will come on ( not always ). .

Usually this code wont clear by turning the key off. You have to actually clear it. So what your describing here is normal. It takes a certain amount of driving without the problem code reoccuring for the light to turn off.

This may be a startup routine to check the TC LOCK UP circuit continuity but why would it change so quickly ( circuit appears OK just before shutting down, but light comes on when started immediately)? Any ideas.

Are you saying you drive the car and there is no light, then you shut it down and the next day you go to drive it and the light is on?

[CoolAirVw]

The lockup torque conv in my 2001 VW TDI 1.8 is not functioning properly.

Tdi in 2001 would be a 1.9 liter.

[n01tk]

Thanks for the reply. At times when I shut the vechicle down the engine light is not on: if I restart the car immediatly after, the light comes on (right away) and stays on. Other times it will stay out for a couple of days but eventually reappears. I am starting to wonder if it is the connector at the ECU.

[CoolAirVw]

Are you sure you dont have other codes? No of course your not because your mechanic is scanning with a generic OBDII code checker.

Check engine light behavior cant be used to diagnose anything. Especially if secondary info is from a Generic OBDII code checker.

Point being. You probably should get a mechanic to work on it that has vag-com. This would at least show they have invested $300 in Vw equipment and might even have worked on a Vw before.

Code P0740 from a generic code checker "translates" into vag code 01192 which is defined as TCC slip, NOT TCC solenoid circuit. There is a big difference in how a TCC solenoid circuit code is diagnosed versus how a TCC slip code is diagnosed.

TCC solenoid circuit code is vag code 00264. If you scan with vag-com and get 00264 then your current line of thinking is ok. If you scan with vag-com and get 01192 then your current line of thinking is a waste of time.

Side note: In some rare instances when your trans is slipping in 4th it will cause a 01192 code. If someone has put parts inside the trans also this code can happen if the planetary ratios are incorrect.

2nd side note: Since you said they overbored the TCC valve train, I'll assume that they didn't do any other valves. The solenoid regulator valve can wear and cause lots of issues including 01192, but usually it will be with a 00652 code, but you might not know if thats in there or not as your scanning with a generic code checker.

[n01tk]

Thanks for the reply. I appreciate your concern with using a vag-com scanner and I am sure he has used one. This transmission tech does all the volkswagon dealers' transmission rebuilds for 3 provinces in Canada. He is located 150 miles away and is a real hassal to get the car to him. He has a very good name and likes to approach each problem with trying to find the problem not just inadvertantly replacing parts. So the first thing ( after he installed a new TC) was bore out the valve body. He has a valve body tester which switches all the solnoids and throughly exercises the valves to ensure everything is working properly. He also has a dyno machine with a v6 engine interfaced with a PC, no question this guy has the test gear. After he discovered it wasn't the valve he replaced the next common failure item, the internal wire harness. Still doing the same thing and coming up with just the one code. I have to bring it back to him and leave it for a week so he can try different things (when the light comes on). I may trade before hand, but if I could find the problem I would hold on to the car for another couple of years. This car, when it is working properly, is fun to drive and very economical. I may try and borrow my buddys' vagcom and have a look. Thanks for your help and I am open to any suggestions for a fix.

[CoolAirVw]

Sounds like you got the best guy in the world working on it for you. Dont know why your wasting time here.

just get it to him and let him fix it.

[n01tk]

Yes your right, he is a good man. I am planning on renting a car for a week and leaving it with him. Thanks for all your comments and I will let you know what he eventually finds.