Automatic Transmission Diagnosis - 4L80-E: Specifications Chevrolet Silverado 2500

Torque Converter Clutch Solenoid Valve

The PCM energizes the Torque Converter Clutch Pulse Width Modulated (TCC PWM) solenoid valve, which is located on the transmission valve body. The TCC PWM solenoid valve acts on the TCC apply valve to control the torque converter clutch application.

The TCC PWM solenoid valve is pulse width modulated by the PCM. This means that the PCM pulses the solenoid so that the hydraulic pressure against the torque converter clutch modulates. This modulated pressure allows the TCC to slip slightly, thus keeping the TCC balanced just at the point of engagement.

One diagnostic code is associated with the TCC PWM solenoid valve. DTC P1860 sets when an electrical fault is detected in the TCC circuit. While DTC P1860 is set, both 4th gear in hot mode and the TCC are inhibited. Shift adapts do not update and the Malfunction Indicator Light (MIL) illuminates. Recovery can occur on the next ignition cycle.

Upshift Control & Torque Converter Clutch Apply

The PCM calculates the upshift points based primarily on 2 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-133047-S09044767142002021200000) . 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 Output Shaft Speed Commanded Gear Slip Speed Solenoid States
3. Place the gearshift lever in the Overdrive position.
4. Accelerate the vehicle using the chosen throttle angle. Hold the throttle steady.
5. As the transmission 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 1-2 seconds of the commanded gear change.
6. Compare the shift speeds to the shift speed chart. See «SHIFT SPEED SPECIFICATIONS»(ref-133047-S09044767142002021200000) . 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. Typical apply speeds in 4th gear range from 45-55 MPH depending on engine size, engine type and axle ratio. 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. Lightly tap and release the brake pedal. The TCC will release.

TORQUE CONVERTER DIAGNOSIS

Note. For additional torque converter information, see appropriate OVERHAUL article.

The Torque Converter Clutch (TCC) is applied by fluid pressure, which is controlled by a PWM solenoid valve. This solenoid valve is located inside of the automatic transmission 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 2 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 Torque Converter Clutch (TCC) shudder is to note when it happens and under what conditions.

TCC shudder which is caused by the transmission 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 transmission 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 condition 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.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS