4L80-E / 4L85-E Automatic Transmission

DTC P0742





Circuit Description with 4L80-E / 4L85-E Automatic Transmission
The Powertrain Control Module (PCM) 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 operating conditions are appropriate for TCC application, the PCM begins the TCC duty cycle to approximately 30 percent. 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 PCM then increases the duty cycle to approximately 60 percent, where regulated apply fluid pressure, applies the converter clutch. The vehicle application determines the TCC apply rate. Once the TCC applies, the duty cycle immediately increases to approximately 70 percent to achieve full apply pressure, in the regulated apply fluid circuit.
The TCC PWM solenoid valve is de-energized by the PCM 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 PCM detects LOW TCC slip when the TCC is commanded OFF, then DTC P0742 sets. DTC P0742 is a type B DTC.

Conditions for Running the DTC
The following conditions occur once per TCC cycle two consecutive times:
^ No MAP sensor DTCs P0106, P0107, or P0108.
^ No AT ISS sensor DTCs P0716 or P0717.
^ No TCC stuck OFF DTC P0741.
^ No AT VSS sensor DTCs P0722 or P0723.
^ No TFP manual valve position switch DTC P1810.
^ No TCC PWM solenoid valve DTC P1860.
^ The engine speed is less than 3,300 RPM.
^ The engine must run more than 475 RPM for greater than 7 seconds.
^ System voltage is 8 - 18 volts.
^ The engine torque must be 176 - 645 Nm (130 - 475 ft. lbs.).
^ The gear range is D4.
^ The commanded gear must be 2nd, 3rd, or 4th.
^ The APP angle must be greater than 15 percent.
^ The Transmission Fluid Temperature (TFT) is 20 - 130°C (68 - 266°F).

Conditions for Setting the DTC
^ The TCC slip speed must be -10 to +10 RPM for at least 3 seconds.
^ All conditions for Setting the DTC are met for 4 occurrences.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in, which the Conditions for Setting the DTC are met.
^ The PCM commands maximum line pressure.
^ The PCM freezes shift adapts.
^ The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
^ The PCM stores the DTC P0742 in PCM history during the second consecutive trip in, which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC
^ For Federal and California emissions, the PCM 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 Federal and California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
^ For vehicles equal to or greater than 15,000 lbs. GVW, the PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring.
^ The PCM cancels the DTC default actions when the fault no longer exists and the ignition switch is OFF long enough in order to power down the PCM.

Diagnostic Aids
^ 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 or skewed APP sensor may set DTC P0742.
^ DTC P0742 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.

Test Description
The number below refers to the step number on the diagnostic table.
3. This step tests the mechanical state of the TCC. When the PCM commands the TCC solenoid OFF, the slip speed should increase.