With 4L80 Transmission

Diagnostic Chart:

Performance:

Circuit Description

The 1-2 Shift Solenoid Valve (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 Valve (2-3 SS Valve) in order to allow four different shifting combinations.

When the Vehicle Control Module (VCM) detects an incorrect gear Ratio, then Diagnostic Trouble Code (DTC) P0751 sets. DTC P0751 is a type D DTC. For California emissions vehicles DTC P0751 is a type B DTC.

Conditions for Setting the DTC

^ No MAP Sensor DTCs P0166, P0107, or P0108.
^ No TP Sensor DTCs P0121, P0122, or P0123.
^ No Output Shaft Speed (OSS) DTC P0502.
^ No Automatic Transmission Input Shaft Speed (A/T ISS) Sensor DTCs P0716 or P0717.
^ No 1-2 SS Valve DTC P0753.
^ No 2-3 SS Valve DTC P0758.
^ No TCC PWM S0l. Valve DTC P1860.
^ No TFP Val. Position Sw. DTC P1810.
^ No Four Wheel Drive DTC P1875.
^ The engine must be running more than 475 RPM for 7 seconds and not in fuel cutoff.
^ The vehicle speed is greater than 4.2 km/h (2.5 mph).
^ The TP Sensor is greater than 12%.
^ The Engine Torque is 88 Nm (70 lb. ft) to the following:

- 470 Nm (375 lb. ft).

^ The Transmission Fluid Temperature (TFT) is greater than 20°C (68°F).
^ The engine vacuum is 0-105 kPa.
^ The engine speed is less than 3650 RPM.
^ Do not put in to Four Wheel Drive Low.
^ All the above conditions are met and one of the following conditions are met:

- 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): 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

^ The VCM commands maximum line pressure.
^ The VCM freezes shift adapts.
^ The VCM illuminates the Malfunction Indicator Lamp (MIL) for California emissions vehicles.

Conditions for Clearing the DTC

1. For California emissions only, the VCM turns OFF the MIL after three consecutive ignition cycles without a failure reported.
2. A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported.
3. The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

Diagnostic Aids

^ Verify that the transmission meets the specifications in the Shift Speed table.
^ Other internal transmission failures can cause more than one shift to occur.
^ 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. Shift Solenoid Valve State and Gear Ratio

Test Description
The numbers below refer to the step numbers on the diagnostic table.

2. This step tests the function of the TFP Val. Position Sw.
3. This step tests whether the scan tool commanded all the shifts, or whether all the shift solenoids responded correctly but all the shifts did not occur.