4L80-E / 4L85-E Automatic Transmission

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
The Vehicle Control Module (VCM) energizes the Torque Converter Clutch Pulse Width Modulated (TCC PWM) solenoid valve by closing the ground circuit. This blocks the exhaust for TCC signal fluid and allows filtered 2-3 drive fluid to feed the TCC signal circuit. When the vehicle's operating conditions are appropriate for TCC application, the VCM begins the TCC duty cycle to approximately 30%. This allows TCC signal fluid pressure to move the converter clutch shift valve into the apply position and direct regulated apply fluid to the torque converter. The VCM then increases (ramps) the duty cycle to approximately 60%, where regulated apply fluid pressure, applies the convener clutch. The vehicle application determines the TCC apply rate. Once the TCC applies, the duty cycle immediately increases to approximately 70% to achieve full apply pressure, in the regulated apply fluid circuit.

The TCC PWM solenoid valve is de-energized by the VCM opening the ground circuit. This action allows the TCC signal fluid to exhaust through the solenoid and blocks filtered 2-3 drive fluid from entering the TCC signal circuit. The loss of fluid pressure in the TCC signal circuit releases the TCC.

If the VCM detects low TCC slip when the TCC is commanded OFF, then DTC P0742 sets. DTC P0742 is a type C DTC. For California emissions vehicles DTC P0742 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
^ No MAP sensor DTCs P0106, P0107, or P0108.
^ No TP sensor DTCs P0121, P0122 or P0123.
^ No OSS DTCs P0502 or P0503.
^ No ISS DTCs P0716 or P0717.
^ No TCC DTCs P0741 or P1860.
^ No TFP manual valve position switch DTC P1810.
^ Engine speed is 900-4,700 RPM.
^ The engine torque must be 75 N.m (60 lb ft) to:
- 500 N.m (400 lb ft) 5.7L
- 625 N.m (500 lb ft) 7.4L
^ No TFP manual valve position switch change within 5.0 seconds.
^ The TFP manual valve position switch must indicate D4, for at least 10 seconds.
^ The commanded gear must be 2nd, 3rd, or 4th.
^ Engine speed is 900-4,700 RPM.
^ The Throttle Position (TP) is 12-100%.
^ Vehicle speed is 7-75 MPH.

CONDITIONS FOR SETTING THE DTC
^ The TCC slip speed must be -10 to +10 RPM for at least 4.0 seconds.
^ All conditions met for 7 occurrences (7.4L, 4 occurrences).

ACTION TAKEN WHEN THE DTC SETS
^ For California emission equipped vehicles the VCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the conditions for Setting the DTC are met. For Non-California emission equipped vehicles the Malfunction Indicator Lamp (MIL) is not illuminated.
^ The VCM commands maximum line pressure
^ The VCM freezes shift adapts.
^ The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Freeze Frame (Calif only) and Failure Records (Calif. and Federal).
^ The VCM stores the DTC P0742 in VCM history during the second consecutive trip (Calif.) or the first trip (Federal) in which the Conditions for Setting the DTC are met.

CONDITIONS FOR CLEARING THE MIL/DTC
^ For California emissions, the VCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
^ A scan tool can clear the MIL/DTC.
^ For California emissions, the VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.
^ For Federal emissions, the VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission related diagnostic fault occurring.
^ The VCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the VCM.

DIAGNOSTIC AIDS
^ First diagnose and clear any engine DTCs or TP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.
^ If the TCC is mechanically stuck ON with the parking brake applied and any gear range selected, the TCC fluid mechanically applies the TCC. TCC fluid mechanically applying the TCC can cause an engine stall.
^ A stuck TP sensor may set a DTC P0742.
^ Inspect the connectors at the VCM, the AT wiring harness and all other circuit connecting points for an intermittent condition. Refer to Testing for Intermittent and Poor Connections in Diagrams.
^ Inspect the circuit wiring for an intermittent condition. Refer to Testing for Electrical Intermittents in Diagrams.

TEST DESCRIPTION
The numbers below refer to the step numbers on the diagnostic table.
3. This step tests the mechanical state of the TCC. When the VCM commands the TCC solenoid OFF, the slip speed should increase.