TCC bouncing on and off

[Precisionair]

Hoping to get some help as I am stumped. I have a 2008 Silverado 1500 with a 4.8 and 4l60e. As the title states the torque converter bounces in and out of lock up. I put a snap on scan gauge on and there are no codes. I watched the data screen and it says it’s locked while it goes in and out, but when I manually select the TCC solenoid on, on the function test it locks up fine and works properly. I’m assuming that this eliminates the valve body,TC and solenoids since they work when turned on via the scan tool? What could be going on here? 

[sefiroxx]

Hoping to get some help as I am stumped. I have a 2008 Silverado 1500 with a 4.8 and 4l60e. As the title states the torque converter bounces in and out of lock up. I put a snap on scan gauge on and there are no codes. I watched the data screen and it says it’s locked while it goes in and out, but when I manually select the TCC solenoid on, on the function test it locks up fine and works properly. I’m assuming that this eliminates the valve body,TC and solenoids since they work when turned on via the scan tool? What could be going on here? 

Computer controls lockup timing based on:
- gear engaged (only 3rd and 4th)
- fluid pressure (needed to ensure that impeller and turbine are close to same rotational speed)
- desired driver action as projected through tps angle or brake. (Ie Large tps indicates desire to accelerate so no lockup as tranny will down shift).
- engine rpm and road speed

Sensors or wires for any of the above could be bad and sending wrong info to computer. I believe there is a tsb on the tps related to your symptom, can't remember if it's applicable to your set up.

First, be sure you are up on maintenance. Tranny fluid change, clean throttle and butterfly, verify cruise control works and brake will release it, check obvious wires, any other dtc's?

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[Precisionair]

Thanks. I’ll check the cruise control tomorrow and see if the brake disengages it. Does the scan tool use a different circuit to engage the solenoid or does it still go through pcm circuit? I’ll also look at the data screen again and take a pic of it with all the data fields and post it. 

[sefiroxx]

Thanks. I’ll check the cruise control tomorrow and see if the brake disengages it. Does the scan tool use a different circuit to engage the solenoid or does it still go through pcm circuit? I’ll also look at the data screen again and take a pic of it with all the data fields and post it. 

It guess through the pcm. Scan tool manual tcc engage bypasses the sensors. A better tool will monitor and show the readings from the sensors and show when the pcm has engaged the tcc.

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[carnau]

14 hours ago, Precisionair said:

Hoping to get some help as I am stumped. I have a 2008 Silverado 1500 with a 4.8 and 4l60e. As the title states the torque converter bounces in and out of lock up. I put a snap on scan gauge on and there are no codes. I watched the data screen and it says it’s locked while it goes in and out, but when I manually select the TCC solenoid on, on the function test it locks up fine and works properly. I’m assuming that this eliminates the valve body,TC and solenoids since they work when turned on via the scan tool? What could be going on here? 

Has this been going on for a while?

[Precisionair]

Thanks. I’ll check the cruise control tomorrow and see if the brake disengages it. Does the scan tool use a different circuit to engage the solenoid or does it still go through pcm circuit? I’ll also look at the data screen again and take a pic of it with all the data fields and post it. 

[Precisionair]

I just got the truck a little over a month ago. It has progressively gotten worse. Big kicker here it was flood damaged. I have replaced BCM that was bad, drained and changed all fluids. I took some pics of scan tool screen. I’ll post in a few. 

[Precisionair]

[Precisionair]

[Precisionair]

[Precisionair]

[Precisionair]

So in two pictures you can see the data screen where it says “TCC ENABLE” it says “yes” well it says that even if the brake is slightly pushed and continues to bounce in and out of lockup. 

On other pictures you can see I lock up the TCC manually and it locks up perfect. Any help deciding this data would be much appreciated. By the way. The brake does cancel cruise control 

[carnau]

What size tire is on it and when it is happening what does the engine load read on your scan tool?

[Precisionair]

Tires are 265/70r17 engine LOD was 42-52 app was 8 and tps around 25 at 50 mph. What determines load anyway? It seams high at light throttle 

[carnau]

It uses MAF signal intake, vehicle speed, vehicle RPM.

 

That's why when you go up a hill or slight incline, your vehicle will drop out of TCC.

I believe you need to find out why your engine load is so high. Really need to get an engine load chart per Speed/RPM

 

If the vehicle thinks it is struggling it will pop in an out of TCC.