4L80-E / 4L85-E Automatic Transmission

Diagnostic Chart:

Schematic:

CIRCUIT DESCRIPTION
The 1-2 Shift Solenoid (1-2 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 shift solenoid (2-3 SS) valve in order to allow four different shifting combinations. When the Vehicle Control Module (VCM) detects a 2-2-3-3 gear ratio or a 1-1-4-4 gear ratio, then DTC P0751 sets. DTC P0751 is a type C DTC. For California emissions vehicles DTC P0751 is a type B DTC.

CONDITIONS FOR RUNNING THE DTC
^ No MAF DTCs P0101, P0102 or P0103.
^ No MAP sensor DTCs P0106, P0107, or P0108.
^ No TP sensor DTCs P0121, P0122, or P0123.
^ No OSS DTCs P0502 or P0503.
^ No AT ISS sensor DTCs P0716 or P0717.
^ No 1-2 SS valve DTC P0753.
^ No 2-3 SS valve DTC P0758.
^ No TFP manual valve position switch DTC P1810.
^ No TCC PWM solenoid valve DTC P1860.
^ The engine must be running more than 475 RPM for 7 seconds.
^ The vehicle speed is greater than 3 km/h (2.0 mph).
^ The TP sensor is greater than 10%. (5.7 & 7.4L), 12% (4.3L).
^ The engine torque is 95 N.m (70 lb ft) 4.3L, 108 N.m (80 lb ft) 5.7L, 7.4L to the following:
- 405 N.m (300 lb ft) 4.3L
- 540 N.m (400 lb ft) 5.7L
- 675 N.m (500 lb ft) 7.4L
^ The Transmission Fluid Temperature (TFT) is greater than 20°C (68°F).

CONDITIONS FOR SETTING THE DTC
All the above conditions are met for running the DTC and one of the following conditions occur:

Stuck Off (after two occurrences)
When the 1-2 SS valve is stuck OFF, first gear is commanded and the ratio is equal to second gear for greater than 2.0 seconds, and 4th gear is commanded with the TCC locked and the ratio equals 3rd gear for greater than 3 seconds.

Stuck On (after five occurrences 5.7L, 7.4L) (seven occurrences 4.3L)
When the 1-2 SS valve is stuck ON, second gear is commanded and the ratio is equal to first gear for greater than 3 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ For California emission equipped vehicles the VCM illuminates the Malfunction Indicator Lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. For Non-California emission equipped vehicles the Malfunction Indicator Lamp (MIL) is not illuminated.
^ The VCM commands maximum line pressure.
^ The VCM inhibits 3-2 downshifts above 25 mph.
^ The VCM freezes shift adapts.
^ The VCM stores the DTC P0751 in VCM history during the second consecutive trip (Calif.) or the first trip (Federal) in which the Conditions for Setting the DTC are met.
^ The VCM records the operating conditions when the Conditions for Setting the DTC are met. The VCM stores this information as Freeze Frame (Calif. only) and Failure Records (Calif. and Federal).

CONDITIONS FOR CLEARING THE MIL/DTC
^ For California emissions, the VCM 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 VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.
^ For Federal emissions, the VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission related diagnostic fault occurring.
^ The VCM cancels the DTC default actions when the fault no longer exists and/or the ignition switch is OFF long enough in order to power down the VCM.

DIAGNOSTIC AIDS
^ First diagnose and clear any engine DTCs or TP 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.
^ Verify that the transmission meets the specifications in the Shift Speed table.
^ Other internal transmission failures can cause more than one shift to occur.

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 whether the scan tool commanded all the shifts, or whether all the shift solenoids responded correctly but all of the correct shifts did not occur.