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 2-3 shift valves. The 2-3 SS valve is a normally-open exhaust valve used with the 1-2 SS valve, in order to allow for four different shift combinations. When the Powertrain Control Module (PCM) detects a 4-3-3-4 gear ratio, then DTC P0756 sets. DTC P0756 is a type C DTC. For California emissions vehicles and vehicles under 8,600 GVW, DTC P0756 is a type A DTC.

Conditions for Running the DTC
^ No MAF sensor DTCs P0101, P0102 or P0103.
^ No MAP sensor DTCs P0106, P0107, or P0108.
^ No TP sensor DTCs P0121, P0122, or P0123.
^ No VSS DTCs P0502 or P0503.
^ No ISS DTCs P0716 or P0717.
^ No TCC Stuck On DTC P0742.
^ No TCC PWM electrical DTC P1860.
^ No TFP manual valve position switch DTC P1810.
^ The engine vacuum is 0 - 105 kPa.
^ No shift solenoid electrical DTCs P0753 or P0758.
^ No transmission component slipping DTC P1870.
^ The engine is running greater than 7 seconds.
^ The vehicle speed is greater than 11 km/h (7 mph).
^ The system voltage is 1 - 18 volts.
^ The throttle angle is greater than 10 percent.
^ The Transmission Fluid Temperature (TFT) is greater than 20°C (68°F) and less than 130°C (266°F).
^ Not in 4WD low.
^ The engine torque must be between 108 Nm (80 ft. lbs.) and:
- 6.0L: 542 Nm (400 ft. lbs.)
- 8.1 L: 881 Nm (650 ft. lbs.)

Conditions for Setting the DTC
^ The commanded gear is 1st and the ratio equals 4th for greater than 2.5 seconds.
^ The commanded gear is 2nd and the ratio equals 3rd for greater than 2.7 seconds.
^ All conditions are met for 2 occurrences.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp (MIL) for California emissions vehicles.
^ The PCM commands a soft landing to 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, California only, and Failure Records, California and Federal.
^ The PCM stores DTC P0756 in PCM history.

Conditions for Clearing the MIL/DTC
^ For 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 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 Federal emissions, 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 incorrect gear ratios to occur.
^ The customer may have concern 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 operating conditions.