P0751

Wiring Diagram:

Circuit Description
The 1-2 shift solenoid valve (1-2 SS Valve) is fed ignition voltage by circuit 1039 and the ground path is provided by the powertrain control module (PCM), depending on the solenoids commanded state. When the PCM commands the solenoid OFF, a ground path is not provided and the filtered line pressure that is fed to the solenoid is exhausted. When the PCM commands the solenoid ON, a ground path is provided and the exhaust port is blocked, stopping the exhaust of line pressure.
The PCM identifies a 1-2 SS Valve condition by monitoring the commanded gear versus gear ratio. If the PCM detects a gear ratio that is outside its limits for a particular commanded gear, then DTC P0751 sets. DTC P0751 is a Type B DTC.

Conditions for Setting the DTC
DTC P0751 sets during the second consecutive trip in which the following conditions occur:
^ No Throttle Position (TP) sensor DTCs P0121, P0122 or P0123 are set.
^ No Vehicle Speed Sensor (VSS) DTCs P0502 or P0503 are set.
^ No A/T ISS sensor DTCs P0716 or P0717 are set.
^ No 1-2 shift solenoid valve electrical DTC P0753 is set.
^ No 2-3 shift solenoid valve electrical DTC P0758 is set.
^ No TFP Valve Position Switch DTC P1810 is set.
^ No TCC PWM Solenoid Valve DTC P1860 is set.
^ The engine speed is greater than 500 RPM for 5 seconds and not in fuel shut off.
^ The transmission is not in PARK or NEUTRAL.
^ The vehicle speed is greater than 8 km/h (5 mph).
^ The throttle position angle is greater than 10%.
^ The transmission fluid temperature is greater than 20°C (68°F).
^ The engine torque is 70-270 N.m (50-200 lb ft).
All of the above conditions are met and Cases 1 and 4 are true twice, or Cases 2 and 3 are true twice.

Case 1
^ First gear is commanded.
^ The gear ratio indicates second gear (1.52:1 to 1.62:1).
^ Condition is met for 2 seconds.

Case 2
^ Second gear is commanded.
^ The gear ratio indicates first gear (2.87:1 to 2.97:1).
^ Condition is met for 3 seconds.

Case 3
^ Third gear is commanded.
^ The gear ratio indicates fourth gear (0.65:1 to 0.75:1).
^ Condition is met for 3 seconds.

Case 4
^ Fourth gear is commanded.
^ The gear ratio indicates third gear (0.95:1 to 1.05:1).
^ Condition is met for 3 seconds.

Action Taken When the DTC Sets
^ The PCM illuminates the Malfunction Indicator Lamp (MIL).
^ The PCM commands maximum line pressure.
^ The PCM freezes shift adapts.
^ The PCM inhibits 3-2 downshifts when the vehicle speed is greater than 48 km/h (30 mph).
^ The PCM stores DTC P0751 in PCM history.

Conditions for Clearing the MIL/DTC
^ A scan tool clears the DTC from the PCM history.
^ The PCM clears the DTC from the PCM history if the vehicle completes 40 consecutive warm-up cycles without an 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
^ Inspect the transmission fluid for sediment.
^ Inspect the transmission filter for debris.
^ Ensure that the scan tool commanded gear has correct solenoid states and ratio. Refer to the Shift Solenoid Valve State and Gear Ratio table.

Test Description

Important: Do not drive the vehicle for an extended period of time because additional internal damage may occur.

The numbers below refer to the step numbers on the diagnostic table.
4. This step replaces the 1-2 shift solenoid valve if no hydraulic or mechanical condition is found.