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Locking Torque Converter Question


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Philbo

So I noticed in the past week or so that my torque converter lock seems to work properly for the first 15 or so minutes of driving and then just stops working. I was going to do some digging in my repair manual when I get the chance, but figured I would throw the question out there. Any ideas? Thanks!

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2seater

I imagine that means it no longer locks up with the attendant rpm drop? It shouldn't work at all until the engine is warmed up and closed loop is enabled. Have you watched the indicator for the TCC in the diagnostic climate control screen? Hopefully that will give a clue if the ECM is not commanding lockup or the lockup fails to operate when signaled. I must say I am not 100% sure if the indicator lights when it has locked or just when signaled, but it's a place to start. I imagine the usual items like fluid level and condition in the transmission is okay?

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Philbo
10 hours ago, 2seater said:

I imagine that means it no longer locks up with the attendant rpm drop? It shouldn't work at all until the engine is warmed up and closed loop is enabled. Have you watched the indicator for the TCC in the diagnostic climate control screen? Hopefully that will give a clue if the ECM is not commanding lockup or the lockup fails to operate when signaled. I must say I am not 100% sure if the indicator lights when it has locked or just when signaled, but it's a place to start. I imagine the usual items like fluid level and condition in the transmission is okay?

Yes so I am referring to once the engine warms up. The TCC does operate with the expected RPM drop at first and seems to disengage and engage properly and then after 10 or 15 min or so of driving it will cease to work.  I honestly only really just noticed this recently and have been trying to narrow down when it does and doesn't work. It pretty consistently works at first and then ceases at some point. The transmission condition has seemed good to me. I did a fluid and filter change about 7k miles or so back. The pan leaks a little thanks to someone going wild with a die grinder on it sometime in the past. It's on the to do list to seal that somehow, but I check the fluid level frequently and it leaks very slowly. Checked the level today and it is good. As for the TCC indicator you mention, is that something for an '88 or '89 with the touchscreen? Mine is a '90 and I couldn't find anything about that in the manual.

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Philbo

Also, is there any harm in driving lengthy stretches of highway without the TCC functioning? I know gas mileage will be affected, but are there any long term negative affects for the transmission?

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2seater

It won't hurt the transmission to drive without lockup, just fuel mileage.

 

I have a '90 also and it isn't as nice and clear as the touch screen cars, but page 8D-7 in the FSM has the chart you are looking for. It is actually just posted in the thread about the engine "bolts or lags" further down the screen. The climate control screen becomes the indicator for many items when in diagnostics. No special screen is required, just get into diagnostics and ecm data and the indicators are active. In this case, the "MED" fan speed illuminates when the TCC locks up and of course goes out when not engaged.

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Philbo

Thanks 2seater. I need to get more familiar with using the diagnostics. I have gone in to read the codes a couple times but am still not used to navigating all the options.  I'll check it out tomorrow hopefully.

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Ronnie
14 minutes ago, Philbo said:

Also, is there any harm in driving lengthy stretches of highway without the TCC functioning?

I've had a switch on my Reatta for years to turn off the TCC so it doesn't engage. I drive with it off most of the time when driving the back roads, which is what most of my driving is. Avoids all the locking and unlocking and makes the drive more enjoyable for me and the car is more responsive when you get on the accelerator.  If I happen to drive on the interstate I flip it back on.

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Padgett

Had the same issue with a 90 Bonne on a trip north. Turns out if the coolant temp drops under about 160F, the TCC will shut off. No code will set.

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Philbo
2 hours ago, Padgett said:

Had the same issue with a 90 Bonne on a trip north. Turns out if the coolant temp drops under about 160F, the TCC will shut off. No code will set.

Hmm interesting. I just replaced the thermostat and did a coolant flush. she runs rock solid at half way on the gauge now so not sure if that could be it. 

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Padgett

Think anything that drops the car out of closed loop will turn off the TCC. Coolant temp is just one I knew.

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Philbo
7 minutes ago, Padgett said:

Think anything that drops the car out of closed loop will turn off the TCC. Coolant temp is just one I knew.

Sorry for the lack of understanding, but what exactly is "closed loop"?

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2seater
4 hours ago, Philbo said:

Sorry for the lack of understanding, but what exactly is "closed loop"?

It is the operating condition when several sensor inputs become active and are used to adjust the operating parameters of the drivetrain. Prior to that time, the engine and associated transaxle operate in what is called open loop, which is pre-programmed settings and charts within the ECM. One of the thresholds to get to closed loop is the coolant temperature to indicate the engine can tolerate leaner mixtures and greater loads where the O2 sensor can adjust fueling to achieve stoichiometric or theoretically perfect balance of fuel and air. I think there is a timer function in the ECM too to engage closed loop in a warm engine after a short start up routine. I don't remember other requirements offhand. There is a loop indicator in the climate control screen when in diagnostic mode on a '90. I think it enables EGR, cruise control, TCC and other items. 

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Padgett

Think one is 100 seconds and other is 25 seconds but from memory. Can just watch the closed loop light in service mode.

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