Transmission Diagnosis

Diagnostic Chart:

Schematic:

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 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 4-3-3-4 gear ratio, then DTC P0756 sets. DTC P0756 is a type A DTC.

CONDITIONS FOR RUNNING THE DTC
^ The system voltage is 8.0-18.0 volts.
^ The engine speed is greater than 475 RPM for greater than 7 seconds.
^ No OSS DTCs P0502 or P0503.
^ No ISS DTCs P0716 or P0717.
^ No TFP manual valve position switch DTCs P1810, P1815, P1816, P1817 or P1818.
^ No shift solenoid electrical DTCs P1842, P1843, P1845 or P1847.
^ TFP manual valve position switch indicates D4, D3, D2 or D1.
^ TFT is 20-130°C (68-265°F).
^ The APP angle is greater than 10%.
^ The vehicle speed is greater than 3.2 km/h (2 mph).
^ The engine torque is 108-644 N.m (80-475 lb ft).
^ The engine speed is below 3,750 RPM.
^ Not in Four Wheel Drive Low.
^ No Four Wheel Drive DTC P1875.

CONDITIONS FOR SETTING THE DTC
Stuck On (for 2 occurrences)
^ First gear is commanded with a ratio equal to fourth gear for greater than 2.8 seconds.
^ Second gear is commanded with a ratio equal to third gear for greater than 2.8 seconds.
^ All conditions for running the DTC are met for 2 occurrences.

Stuck Off (for 7 occurrences)
Third is commanded with a ratio equal to second gear for 2.8 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 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 clears the DTC from PCM history.
^ For Federal and California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 consecutive 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 consecutive 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.
^ First, diagnose and clear any engine DTCs or APP sensor codes that are present. Then inspect for any transmission DTCs that may have reset.
^ Refer to Shift Solenoid Valve State and Gear Ratio table.

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.