GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Isuzu 🢒 2005 🢒 Ascender - 2WD 🢒 Accessories 🢒 Navigation Systems 🢒 DTC P0751

DTC P0751 4.2L


Object Number: 42270 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics 4.2L
OBD II Symbol Description Notice

Circuit Description

The 1-2 shift solenoid (SS) valve controls the fluid flow acting on the 1-2 and 3-4 shift valves. The 1-2 SS valve is a normally-open exhaust valve that is used with the 2-3 SS valve, in order to allow 4 different shifting combinations.

If the powertrain control module (PCM) detects a 2-2-3-3 shift pattern, then DTC P0751 sets. DTC P0751 is a type B DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0751 1-2 Shift Solenoid Valve Performance - No First or Fourth Gear

Conditions for Running the DTC
    • No VSS DTCs P0502 or P0503.
    • No TCC stuck ON DTC P0742.
    • No 1-2 SS valve DTC P0753.
    • No 2-3 SS valve DTC P0758.
    • No TP sensor DTCs P1120 or P1220.
    • The engine speed is greater than 450 RPM for 5 seconds.
    • The engine is not in fuel cutoff.
    • The gear range is D4.
    • The TP angle is 10 percent or greater.
    • The transmission fluid temperature is 20-130°C (68-266°F).
    • The system voltage is 10-18 volts.
    • The engine torque is 68-542 N·m (50-400 lb ft).
    • The transmission output speed is 150 RPM or greater.
    • The transfer case ratio in 4WD Low is 0.9 to 1.2.
    • The transfer case ratio in 4WD High is 2.6 to 2.85.

Conditions for Setting the DTC

DTC P0751 sets if both of the following conditions occur twice:

Condition 1

    • The PCM commands first gear for 2 seconds.
    • The estimated gear ratio is 1.2-1.8.
    • The torque converter efficiency is greater than or equal to 0.35.
    • All conditions are met for 0.5 seconds.

Condition 2

    • The PCM commands fourth gear for 1 second.
    • The estimated gear ratio is 0.95-1.15.
    • All conditions are met for 6 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 D2 line pressure.
    • The PCM commands TCC OFF.
    • The PCM inhibits fourth gear in hot mode.
    • The PCM freezes transmission adaptive functions.
    • 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 DTC P0751 in PCM history.

Conditions for Clearing the MIL/DTC
    • 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.
    • The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
    • The PCM 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 PCM.

Diagnostic Aids
    • Verify that the transmission meets the specifications in the Shift Speed table.
    • Refer to the Shift Solenoid Valve State and Gear Ratio table.

Test Description

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

  1. This step tests that the PCM commanded all shifts, that all shift solenoid valves responded correctly, but that all the shifts did not occur.

DTC P0751 (4.2L)

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the powertrain control module (PCM).

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Drive the vehicle in D4 range under the following conditions:

    6. Accelerate the vehicle, ensuring that the PCM commands 1st, 2nd, 3rd and 4th gears.

Did you detect a 2-2-3-3 shift pattern?

Go to Step 3

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

3

Inspect the shift solenoid/hydraulic circuit for the following conditions:

    • An internal malfunction
    • Damaged seals on the shift solenoid valve
        Refer to Shift Solenoid Leak Test .

Did you find and correct the condition?

Go to Step 4

--

4

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Drive the vehicle in D4 range under the following conditions, only if traffic and road conditions permit:

    4. Hold the throttle at 20 percent and accelerate to 88 km/h (55 mph).

  4. Select Specific DTC.
  5. Enter DTC P0751.

Has the test run and passed?

Go to Step 5

Go to Step 2

5

With the scan tool, observe the stored information, capture info, and DTC Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information

System OK

DTC P0751 5.3L


Object Number: 42270 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics 5.3L
OBD II Symbol Description Notice

Circuit Description

The 1-2 shift solenoid (SS) valve controls the fluid flow acting on the 1-2 and 3-4 shift valves. The 1-2 SS valve is a normally-open exhaust valve that is used with the 2-3 SS valve, in order to allow 4 different shifting combinations.

If the transmission control module (TCM) detects a 2-2-3-3 shift pattern, then DTC P0751 sets. DTC P0751 is a type B DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0751 1-2 Shift Solenoid Valve Performance - No First or Fourth Gear

Conditions for Running the DTC
    • No OSS DTCs P0722 or P0723.
    • No TCC performance DTC P0742, P0894.
    • No shift solenoid electrical DTCs P0973, P0974, P0976, or P0977.
    • The ignition voltage is 8-18 volts.
    • The engine RPM is 150-6,500 RPM for greater than 5 seconds.
    • The transmission fluid temperature is 20-130°C (68-266°F).
    • The throttle position is 10 percent or greater.
    • The output shaft speed is 150 RPM or greater.

Conditions for Setting the DTC

Both of the following conditions must occur twice during the same trip:

    • Fail Case 1: The TCM commands 1st gear and the resulting gear ratio is 1.23:1-1.84:1 for 0.5 seconds.
    • Fail Case 2: The TCM commands 4th gear and the resulting gear ratio is 0.95:1-1.15:1 for 1 second.

Action Taken When the DTC Sets
    • The TCM requests the ECM to illuminate the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
    • The TCM commands maximum line pressure.
    • The TCM freezes transmission adaptive functions.
    • At the time of the first failure, the TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as a Failure Record.
    • At the time of the second failure, the ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as a Freeze Frame.
    • The TCM stores DTC P0751 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

Conditions for Clearing the DTC
    • The ECM turns OFF the MIL after the 4th consecutive drive trip in which the TCM does not send a MIL illumination request.
    • A scan tool can clear the DTC.
    • 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 ignition is OFF long enough in order to power down the TCM.

Diagnostic Aids
    • If you clear DTC P0751, and then cannot reset DTC P0751, the following conditions may exist:
       - Fluid contamination
       - Plugged fluid circuits
       - Restricted fluid circuits
    • Refer to Shift Solenoid Valve State and Gear Ratio .

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step tests that the TCM commanded all shifts, that all shift solenoid valves responded correctly, but that all the shifts did not occur.

DTC P0751

Step

Action

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the transmission control module (TCM).

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Drive the vehicle in D4 range under the following conditions:

    6. Accelerate the vehicle, ensuring that the TCM commands 1st, 2nd, 3rd, and 4th gears.

Did you detect a 2-2-3-3 shift pattern?

Go to Step 3

Go to Diagnostic Aids

3

Inspect the shift solenoid/hydraulic circuit for the following conditions:

    • An internal malfunction
    • Damaged seals on the shift solenoid valve
        Refer to Shift Solenoid Leak Test .

Did you find and correct the condition?

Go to Step 4

--

4

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Drive the vehicle in D4 range under the following conditions, only if traffic and road conditions permit:

    4. Hold the throttle at 20 percent and accelerate to 88 km/h (55 mph).

  4. Select Specific DTC.
  5. Enter DTC P0751.

Has the test run and passed?

Go to Step 5

Go to Step 2

5

With the scan tool, observe the stored information, capture info, and DTC Info.

Does the scan tool display any DTCs that you have not diagnosed?

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK