4L80-E / 4L85-E Automatic Transmission
DTC P0751 (6.6L)
Circuit Description
The 1-2 shift solenoid (SS) valve controls the fluid flow action on the 1-2 and the 3-4 shift valves. The 1-2 SS valve is a normally open exhaust valve that is used with the 2-3 SS in order to allow four different shifting combinations.
When the transmission control module (TCM) detects a 2-2-3-3 gear ratio, then DTC P0751 sets. DTC P0751 is a type C DTC. For California emissions vehicles DTC P0751 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0751 1-2 Shift Solenoid (SS) Valve Performance - No First or Fourth Gear
Conditions for Running the DTC
^ No MAF sensor DTC 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 AT ISS sensor DTCs P0716 or P0717.
^ No TCC Stuck ON DTC P0742.
^ No shift solenoid electrical DTC P0753 or P0758.
^ No Transmission Component Slipping DTC P0894.
^ No TFP manual valve position switch DTC P1810.
^ No TCC PWM solenoid valve DTC P2761.
^ The system voltage is 10 - 18 volts.
^ The AT OSS is greater than 7 RPM.
^ Not in 4WD Low.
^ AT ISS is greater than 7 RPM.
^ The TP sensor is 10-100 percent.
^ The engine torque must be between 108 Nm (80 ft. lbs.) and:
^ 4.8L: 542 Nm (400 ft. lbs.)
^ 6.0L: 576 Nm (425 ft. lbs.)
^ No TFP manual valve position switch change within 6 seconds.
^ The TFP manual valve position switch indicates D4.
^ The transmission fluid temperature (TFT) is greater than 20°C (68°F) and less than 130°C (266°F).
Conditions for Setting the DTC
^ The commanded gear equals 1st and the ratio equals 2nd for greater than 2 seconds.
^ The commanded gear equals 4th with the torque converter clutch (TCC) locked and the ratio equals 3rd for greater than 3.75 seconds.
^ All conditions are met for 2 occurrences.
Action Taken When the DTC Sets
^ For California emission equipped vehicles, the TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. For Federal emission equipped vehicles, the MIL is not illuminated.
^ The TCM commands maximum line pressure.
^ The TCM freezes transmission adaptive functions.
^ The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Freeze Frame, California only, and Failure Records, California and Federal.
^ The TCM stores the DTC P0751 in TCM history during the second consecutive trip, California, 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 TCM 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 TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
^ For Federal emissions, the TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring.
^ The TCM 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 TCM.
Diagnostic Aids
^ Verify that the transmission meets the specifications in the Shift Speed table. Refer to Shift Speed.
^ Other internal transmission failures can cause more than one shift to occur.
^ DTC P0751 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.
2. This step tests that the TCM commanded all shifts, that all shift solenoid valves responded correctly, but that all the shifts did not occur.
