Is this typical torque converter lockup/unlock?
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From: Waukesha, WI, US
Is this typical torque converter lockup/unlock?
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.
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.
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From: Edmonton, AB Canada
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.
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.
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Certified Car Nut
Joined: Jul 2003
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From: Robbinsdale, MN
Originally Posted by Sol
Yea, around 55 or so is when it will go off an on frequently. And when you give it more gas, it will release.
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From: Waukesha, WI, US
Originally Posted by willwren
Bonnevilles should lockup in the 48mph range. Is the LSS TC lockup different?
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Joined: Nov 2002
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From: Chattanooga, Tennessee
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.
I wish it would just lock and stay locked until the brakes were applied or the transmission needed to shift.