Automatic Transaxle Diagnosis - 4T40-E & 4T45-E: Specifications Pontiac Sunfire I

Torque Converter Clutch Pulse Width Modulated Solenoid Valve

The Torque Converter Clutch (TCC) solenoid valve is a normally closed, Pulse Width Modulated (PWM) solenoid used to control the apply and release of the converter clutch. The PCM operates the solenoid with a negative duty cycle at a fixed frequency of 42 Hz to control the rate of TCC apply and release. The solenoid's ability to ramp the TCC apply and release pressures results in smoother TCC operation.

When vehicle operating conditions are appropriate to apply the TCC, the PCM immediately increases the duty cycle to about 42 percent. The PCM then ramps the duty cycle up to about 90 percent to achieve full TCC apply pressure. The rate at which the PCM increases the duty cycle controls the TCC apply. Similarly, the PCM also ramps down the TCC solenoid duty cycle to control the TCC release.

Some operating conditions prevent or enable the TCC apply under various conditions. Also if the PCM receives a high voltage signal from the brake switch, indicating that the brake pedal is depressed, the PCM immediately releases the TCC.

Upshift Control & Torque Converter Clutch Apply

The PCM calculates the upshift points based primarily on two inputs: throttle angle and vehicle speed. When the PCM determines that conditions are met for a shift to occur, the PCM commands the shift by closing or opening the ground circuit for the appropriate solenoid.

1. Choose a throttle position of 10, 25 or 50 percent. See «SHIFT SPEED SPECIFICATIONS»(ref-155792-S16236618852003062500000) . All throttle angles shown should be tested to cover the normal driving range.
2. Monitor the following scan tool parameters: Throttle Angle Vehicle Speed Engine Speed Commanded Gear Slip Speed Solenoid States
3. Place the gearshift lever in the "D" (Overdrive) position.
4. Accelerate the vehicle using the chosen throttle angle. Hold the throttle steady.
5. As the transaxle upshifts, note the vehicle speed when the shift occurs for each gear change. There should be a noticeable shift feel or engine speed change within 1 to 2 seconds of the commanded gear change.
6. Compare the shift speeds to the shift speed chart. See «SHIFT SPEED SPECIFICATIONS»(ref-155792-S16236618852003062500000) . Shift speeds may vary slightly due to transmission fluid temperature or hydraulic delays in responding to electronic controls. Note any harsh, soft or delayed shifts or slipping. Note any noise or vibration.
7. Repeat steps 1 - 6 to complete all throttle angles.
8. Check for TCC apply in 3rd and 4th gear. Note the TCC apply point. When the TCC applies, there should be a noticeable drop in engine speed and a drop in slip speed to below 100 RPM. If the TCC apply can not be detected, check for DTCs. For TCC apply speeds, see «SHIFT SPEED SPECIFICATIONS»(ref-155792-S16236618852003062500000) . Lightly tap and release the brake pedal. The TCC will release on most applications.

TORQUE CONVERTER DIAGNOSIS

The Torque Converter Clutch (TCC) is applied by fluid pressure, which is controlled by a Pulse Width Modulation (PWM) solenoid valve. This solenoid valve is located inside of the automatic transaxle assembly. The solenoid valve is controlled through a combination of computer controlled switches and sensors.

Torque Converter Stator

The torque converter stator roller clutch can have two different malfunctions

1. The stator assembly freewheels in both directions.
2. The stator assembly remains locked up at all times.

Torque Converter Clutch Shudder

The key to diagnosing TCC shudder is to note when it happens and under what conditions.

TCC shudder which is caused by the transaxle should only occur during the apply or the release of the converter clutch. Shudder should never occur after the TCC plate is fully applied.

If the shudder occurs while the TCC is applying, the problem can be within the transaxle or the torque converter. Something is causing one of the following conditions to occur

1. Something is not allowing the clutch to become fully engaged.
2. Something is not allowing the clutch to release.
3. The clutch is releasing and applying at the same time.

One of the following conditions may be causing the problem to occur

1. Leaking turbine shaft seals.
2. A restricted release orifice.
3. A distorted clutch or housing surface due to long converter bolts.
4. Defective friction material on the TCC plate.