4L80-E / 4L85-E Automatic Transmission

DTC P0756





Circuit Description with 4L80-E / 4L85-E Automatic Transmission
The 2-3 Shift Solenoid (SS) valve controls fluid flow acting on the 2- shift valve. The 2-3 SS valve is a normally open exhaust valve that is used with the
1-2 Shift Solenoid (SS) valve to allow four different shift combinations.
When the Powertrain Control Module (PCM) detects a non first gear ratio while first gear is commanded or a first gear ratio while fourth gear is commanded, then DTC P0756 sets. DTC P0756 is a type A DTC.

Conditions for Running the DTC
^ No TFT sensor DTCs P0712 or P0713.
^ No AT ISS sensor DTCs P0716 or P0717.
^ No VSS sensor DTCs P0722 or P0723.
^ No shift solenoid electrical DTCs P0753 or P0758.
^ No TFP manual valve position switch DTC P1810.
^ System voltage is 8 - 18 volts.
^ The vehicle speed is greater than 3 km/h (2 mph).
^ The APP angle is greater than 10 percent.
^ The Transmission Fluid Temperature (TFT) is 20 - 130°C (68 - 266°F).
^ The engine torque is 100 - 644 Nm (80 - 475 ft. lbs.).
^ The engine speed is 475 - 3,750 RPM for at least 7 seconds.

Conditions for Setting the DTC
All of the above Conditions for Running the DTC are met and either of the two following conditions occur:

Stuck On - after 2 occurrences
^ First gear is commanded and the ratio equals 4th gear for greater than 2.75 seconds.
^ Second gear is commanded and the gear ratio equals 3rd for greater than 2.75 seconds.

Stuck Off - after 7 Occurrences
Third gear is commanded and the gear ratio equals 2nd for greater than 3.25 seconds.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp (MIL).
^ The PCM commands 2nd gear.
^ 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 DTC P0756 in PCM history.

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
^ Verify that the transmission meets the specifications in the Shift Speed table.
^ Other internal transmission failures may cause similar shift patterns.
^ The customer may complain of an engine over-rev condition or neutral condition in 4th gear.
^ DTC P0756 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 numbers below refer to the step numbers on the diagnostic table.
2. This step tests the function of the TFP manual valve position switch.
3. This step tests for a selected gear ratio versus a ratio not obtainable under normal driving conditions.