I'm on the freeway, over 50 mph, the TC locks up. I lift off the gas (say, to slow down for traffic, or going over a small hill), when I get back on the gas the TC has unlocked, the revs go up and then the TC locks up again. It doesn't happen if I don't let off the gas all the way. I'm not getting back on the throttle hard, this is "gentle" highway driving.

This happens a lot during my communte to and from work. Lots of gradual hills and slowing down for traffic. The LSS has done this since I've had it, I'm wondering if this is what is supposed to happen, or if the TC should stay locked under those conditions.

Torque Converter Clutch Solenoid: Description and Operation
The purpose of the Transmission Converter Clutch (TCC) feature is to eliminate the power loss of the torque converter stage when the vehicle is in a cruise mode. The TCC system uses a solenoid operated valve to engage the TCC which couples the engine flywheel to the input shaft of the transmission through the torque converter. This reduces the slippage losses in the converter, which increases fuel economy. Another solenoid (pulse width modulator or PWM solenoid) is used to regulate fluid pressure to the TCC to "cushion" the apply of the clutch.

For the converter clutch to apply, at least two conditions must be met.

- Internal transmission fluid pressure must be correct.

- The PCM completes a ground circuit to energize the TCC solenoid in the transmission, which moves a check ball in the fluid line.

The PCM controls the TCC apply solenoid by looking at several sensors.

- Engine must be in closed loop operation.

- Vehicle Speed Sensor (VSS). Speed must be above a certain value before the clutch can apply.

- Coolant Temperature Sensor (CTS). Engine must be warmed up before the clutch can apply.

- The 4th gear switch is used as a input to the PCM. The PCM uses the switch signal for TCC engage and disengage points.

- Throttle Position Sensor (TPS). After the converter clutch applies, the PCM uses the information ftom the TPS to release the clutch when the car is accelerating or decelerating at a certain rate.

- Another switch used in the TCC circuit is a brake switch which opens the 12 volt supply to the TCC solenoid when the brake is depressed.

Yea, around 55 or so is when it will go off an on frequently. And when you give it more gas, it will release.

Thanks!

Sounds normal.

Yeah, that always kinda freaks me out. Feels like the tranny ain't sure what gear it wants to be in. I found a simple solution, tho. PUNCH IT!! ZoomZoom fixes all....

Bonnevilles should lockup in the 48mph range. Is the LSS TC lockup different?

my '87 starts letting the trans lock up in the 35 mph range and on up, i'm sure something is a little askew under the hood but for now I'll ride it out
Mike Diaz

Don't think so...same engine, transmission, and PCM, AFAIK. I do get lockup around 48 mph, it was the unlocking after letting off the gas that I was wondering about.

Apparently this is normal behavior for most if not all GM automatics. Mine locks and unlocks literally dozens of times a day.

I wish it would just lock and stay locked until the brakes were applied or the transmission needed to shift.