P0751
DTC P0751 (Diesel)
Circuit Description
The 1-2 shift solenoid (SS) valve controls the fluid flow 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 valve to allow four different shifting combinations.
When the powertrain control module (PCM) detects a 2-2-3-3 or a 1-1-4-4 gear ratio, then DTC P0751 sets. DTC P0751 is a type B DTC.
Conditions for Running the DTC
- No MAP sensor DTCs P0106, P0107, or P0108.
- No VSS DTCs P0722 or P0723.
- No ISS sensor DTCs P0716 or P0717.
- No TCC DTCs P0741 or P0742.
- No 1-2 shift solenoid valve DTC P0753.
- No 2-3 shift solenoid valve DTC P0758.
- No TFP manual valve position switch DTC P1810.
- No TCC P1860.
- The engine must be running for at least 7 seconds.
- The vehicle speed is greater than 3 km/h (2 mph).
- The APP angle is greater than 10 percent.
- System voltage is 8 - 18 volts.
- The engine torque is 108 - 644 Nm (80 - 475 ft. lbs.).
- The transmission fluid temperature (TFT) is greater than 20°C (68°F) and less than 130°C (255°F).
- The engine speed is less than 3,750 RPM.
Conditions for Setting the DTC
All the above conditions are met for Running the DTC and one of the following conditions occur:
Stuck Off - for two occurrences
- First gear is commanded and the gear ratio is equal to second gear for greater than 1.5 seconds.
- Fourth gear is commanded, with TCC locked, and the gear ratio equals third gear for greater than 3 seconds.
Stuck On - for five occurrences
Second gear is commanded and the gear ratio equals first gear for greater than 2.2 seconds.
Action Taken When the DTC Sets
- The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
- The PCM commands maximum line pressure.
- The PCM freezes shift adapts.
- The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
- The PCM stores the DTC P0751 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
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 can clear the MIL/DTC.
- For Federal and California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 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 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
- 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.
- 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.
- Verify that the transmission meets the specifications in the Shift Speed.
- Other internal transmission failures may cause incorrect gear ratios 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 can command the shift solenoids correctly, but not all the shifts occurred.