No TCC unlock signal at zero throttle
03-21-2014, 04:21 PM
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No TCC unlock signal at zero throttle I have a level 2 Performabuilt 4L60E, with a 2800 stall Vig TC. They have been working great together for a couple of years, but in the last couple of weeks they have developed a couple of problems.
A few weeks ago my TC lockup went from firm and almost instantaneous to soft and slow. It takes a couple of seconds for the TC to lock up, and even when it does, it doesn't feel full locked right away. I may have to drive a couple of miles before it feels fully locked.
Last week my TC stopped unlocking when I would let off the gas. I talked to Frank at Performabuilt and followed a few of his suggestions. I wired in an LED light to see if and when my PCM is sending a lock or unlock signal.
Results from the signal check are as follows: PCM sends lock signal at around 43 MPH. When I let off the gas, my pcm continues sending the lock signal. If I punch the gas quickly the PCM sends an unlock signal, and if I press the brake the PCM sends an unlock signal.
This seemed to indicate a possible faulty Throttle Pos. Sensor, so I changed the part, but my PCM and TC still act the same.
Any ideas Folks?...
A few weeks ago my TC lockup went from firm and almost instantaneous to soft and slow. It takes a couple of seconds for the TC to lock up, and even when it does, it doesn't feel full locked right away. I may have to drive a couple of miles before it feels fully locked.
Last week my TC stopped unlocking when I would let off the gas. I talked to Frank at Performabuilt and followed a few of his suggestions. I wired in an LED light to see if and when my PCM is sending a lock or unlock signal.
Results from the signal check are as follows: PCM sends lock signal at around 43 MPH. When I let off the gas, my pcm continues sending the lock signal. If I punch the gas quickly the PCM sends an unlock signal, and if I press the brake the PCM sends an unlock signal.
This seemed to indicate a possible faulty Throttle Pos. Sensor, so I changed the part, but my PCM and TC still act the same.
Any ideas Folks?...
03-21-2014, 04:54 PM
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Even at 0% throttle the TCC will lock at a certain speed, a relatively low speed.
Therefore "let off the gas" is not expected to unlock the TCC.
There is also a programmed speed at which the TCC should unlock. If the PCM is still sending the lock signal below that speed (according to your LED), you either have a short in the wiring or a faulty PCM.
I assume of course that the tune did not change.
Perhaps you will discover that that PCM is signalling the TCC to unlock (confirm with your LED) but that the TCC still feels engaged. This indicates that the converter has gone bad - in particular the lockup clutch likely overheated and warped and is therefore not engaging nor disengaging exactly when commanded. Based on your 2nd paragraph, this is my hypothesis.
Therefore "let off the gas" is not expected to unlock the TCC.
There is also a programmed speed at which the TCC should unlock. If the PCM is still sending the lock signal below that speed (according to your LED), you either have a short in the wiring or a faulty PCM.
I assume of course that the tune did not change.
Perhaps you will discover that that PCM is signalling the TCC to unlock (confirm with your LED) but that the TCC still feels engaged. This indicates that the converter has gone bad - in particular the lockup clutch likely overheated and warped and is therefore not engaging nor disengaging exactly when commanded. Based on your 2nd paragraph, this is my hypothesis.
03-21-2014, 05:42 PM
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Thanks for your reply mrvedit.
My TC does unlock when I fall below 43 mph, and my LED confirms this. In the first three years that I ran this trans/TC combo, my TC has always unlocked when I was at zero throttle, and in the past three years since having both the trans and TC rebuilt by the manufacturers it has always unlocked at zero throttle. You are correct that I have not changed my tune at all during this time.
I tend to agree with the hypothesis that I may have a bad PCM, as it has very high mileage, but I plan to look into wiring as well. Also, we have had very cold weather here in NM for months, and this issue only arose after we started getting somewhat warmer temps. I'm thinking there may be a failing solder joint in the PCM or something like that, caused by the temperature swings.
I totally rebuilt this car onto a donor chassis almost a year ago, so wiring could be an issue.
Let me know if you think of any other possible resolutions.
My TC does unlock when I fall below 43 mph, and my LED confirms this. In the first three years that I ran this trans/TC combo, my TC has always unlocked when I was at zero throttle, and in the past three years since having both the trans and TC rebuilt by the manufacturers it has always unlocked at zero throttle. You are correct that I have not changed my tune at all during this time.
I tend to agree with the hypothesis that I may have a bad PCM, as it has very high mileage, but I plan to look into wiring as well. Also, we have had very cold weather here in NM for months, and this issue only arose after we started getting somewhat warmer temps. I'm thinking there may be a failing solder joint in the PCM or something like that, caused by the temperature swings.
I totally rebuilt this car onto a donor chassis almost a year ago, so wiring could be an issue.
Let me know if you think of any other possible resolutions.