Scan Gauge: TCC Slip. What is this?

[Carey Frennier]

Today I was driving from one Thanksgiving to another. I was passing a car. Throttle was at 35% as they were going very slow.



All the sudden my message center went orange or yellow (I'm color blind) and it had a big wrench on it.



I went to my Aeroforce Interceptor Scan Gauge function. It found no codes. I was puzzled.



The truck felt like it was in OD off but the gauge confirmed 6th gear engaged. The RPMs were about 500-700 higher than normal in this gear at 60mph.



Also, normally the TCC Slip reading under low load cruise control, at 60mph in 6th gear is between 7 and 0. It's much higher when stopped in gear holding the brake and when at WOT.



I went into the Aeroforce Interceptor's scan gauge mode again and scanned for codes again.



Nothing. I cleared it anyway and all the sudden everything went back to normal.



I have no idea what happened.

 

[Carey Frennier]

I thought this had something to do with the torque converter lock up but I need schooling on what all that is.



Who feels like throwing down some education?!

 

[Supercharged SVT]

i saw the same code on they Dyno when we forced the convertor to lock up. he cleared it and it never came back. he says that the converter needs to be forced to lock up since it does not do it on its own. to achieve accurate dyno tuning a lock up forced action is required by the tuner. then he puts it back after. the transmission on a 2010 is a separate ecu.

 

[Carey Frennier]

I know it's a seperate ecu but I'm unclear as to the function it plays on the track and in day to day driving.



I'm assuming a fully locked converter is transferring the max power to the ground.



However, mine usually shows more slip at WOT according to the gauge.



Maybe it's torque converter slip rpm or something. That would make more sense. Because at low rpm or cruise control it wouldn't be working as hard as it would at WOT.

 

[scott degroot]

TCC stands for Torque Converter Clutch. TCC slip is how much the torque converter is slipping...obviously.



All torque converters have to slip otherwise when the vehicle was stopped the trans and the engine would be locked together and the vehicle would stall, just like having a manual trans vehicle and trying to stop the vehicle without pushing the clutch in.



There is a solenoid inside the trans that allows fluid to flow to a circuit inside the torque converter, this application, or release depending on transmission, of fluid and pressure is what causes the torque converter to lock up...turn the same rpms as the engine.



Typically torque converter lockup isn't commanded until vehicle speed is around 45 mph (this is just a generic spec, different vehicles have different speeds) and engine demand is minimal.



Torque converter slippage is monitored by comparing the input shaft speed sensor with the output shaft speed sensor and/or the turbine shaft speed sensor and doing the math. Years ago lockup was only commanded while in overdrive but many modern day transmissions will lock the torque converter from 2nd gear on up, this is to help with fuel economy.



The key thing to remember about torque converter lockup is that it should only occur while engine demand is low, such as maintaining a steady speed on a relatively flat road. When engine load is increased, such as accelerating or climbing a grade, the clutch should unlock so as to not drag the engine down.



While the torque converter clutch is locked the difference between input shaft speed and output shaft speed should be less than approx. 150 rpms (vehicle dependent).



Hope this helps somewhat

 

[Carey Frennier]

It does.



I wonder what the heck happened. The trans has been perfect since.



I wonder if it just was a fluke thing. Stranger things have happened!

 

[scott degroot]

I would keep an eye on it as it could be a sign of things to come. If you knew the normal slip speed readings and also the commanded % of the TCC solenoid at a given condition you could determine if you are actually having an issue. Say normally the slip speed is 50 rpm with a solenoid commanded at 50% adn now under the same conditions slip speed is 50 rpms but the solenoid is now commanded to 85%...something would be going on there.

 

[Carey Frennier]

Normal is 15-0 rpm and this was 250-190rpm slip speed.



I'll have to see if I can find a solenoid command % in the PID selector.

 

[scott degroot]

I wonder if you are going to run into a problem with the engine being SCed and running a stock converter. Converters start acting weird when the engine puts out more than the converters are designed to handle

 

[Carey Frennier]

Well, the tq and tran are a ZF platform trans. They are identic to the BMW M series sub trans. Most of the driveline is good until a little over 430-460rwhp. So hopefully Its nothing serious.



If it is, I'm switching to a built mustang 5 speed automatic trans.