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Makes 🢒 Chevrolet 🢒 2007 🢒 Express - AWD 🢒 Safety and Security 🢒 Supplemental Inflatable Restraints 🢒 DTC P0751

DTC P0751 4.8L and 6.0L


Object Number: 40795 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics (4.8L and 6.0L)

Circuit Description

The 1-2 shift solenoid (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 SS in order to allow four different shifting combinations.

When the powertrain control module (PCM) detects a 2-2-3-3 gear ratio, then DTC P0751 sets. DTC P0751 is a type C DTC. For California emissions vehicles 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 MAF sensor DTC P0101, P0102 or P0103.
    • No MAP sensor DTCs P0106, P0107, or P0108.
    • No TP sensor DTCs P0121, P0122 or P0123.
    • No VSS DTCs P0502 or P0503.
    • No AT ISS sensor DTCs P0716 or P0717.
    • No TCC Stuck ON DTC P0742.
    • No shift solenoid electrical DTC P0753 or P0758.
    • No Transmission Component Slipping DTC P0894.
    • No TFP manual valve position switch DTC P1810.
    • No TCC PWM solenoid valve DTC P2761.
    • The system voltage is 10-18 volts.
    • The AT OSS is greater than 7 RPM.
    • Not in 4WD Low.
    • AT ISS is greater than 7 RPM.
    • The TP sensor is 10-100 percent.
    • The engine torque must be between 108 N·m (80 lb ft) and:
       - 4.8L: 542 N·m (400 lb ft)
       - 6.0L: 576 N·m (425 lb ft)
    • No TFP manual valve position switch change within 6 seconds.
    • The TFP manual valve position switch indicates D4.
    • The transmission fluid temperature (TFT) is greater than 20°C (68°F) and less than 130°C (266°F).

Conditions for Setting the DTC
    • The commanded gear equals 1st and the ratio equals 2nd for greater than 2 seconds.
    • The commanded gear equals 4th with the torque converter clutch (TCC) locked and the ratio equals 3rd for greater than 3.75 seconds.
    • All conditions are met for 2 occurrences.

Action Taken When the DTC Sets
    • For California emission equipped vehicles, the PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. For Federal emission equipped vehicles, the MIL is not illuminated.
    • The PCM commands maximum line pressure.
    • 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, California only, and Failure Records, California and Federal.
    • The PCM stores the DTC P0751 in PCM history during the second consecutive trip, California, or the first trip, Federal, in which the Conditions for Setting the DTC are met.

Conditions for Clearing the MIL/DTC
    • For 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 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 Federal emissions, 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
    • Verify that the transmission meets the specifications in the Shift Speed table. Refer to Shift Speed .
    • Other internal transmission failures can cause more than one shift to occur.
    • 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.

Test Description

The number below refers to the step number 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.

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 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

3
  1. Inspect the shift solenoid/hydraulic circuit for the following conditions:
    2. • 1-2 shift solenoid mechanically stuck OFF
    • Refer to Shift Solenoid Leak Test .
    • 1-2 shift valve stuck in the released position
    • Damaged seals on the 1-2 shift solenoid valves
    • Refer to Shift Solenoid Leak Test .
  2. Clean and inspect the related valves, bores and the valve body for debris or contamination restricting valve movement. Refer to Control Valve Body Cleaning and Inspection.

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 condition, only if traffic and road conditions permit:

    4. Hold the throttle at 40% and accelerate to 89 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

DTC P0751 6.6L


Object Number: 40795 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics (6.6L)

Circuit Description

The 1-2 shift solenoid (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 SS in order to allow four different shifting combinations.

When the transmission control module (TCM) detects a 2-2-3-3 gear ratio, 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 AT ISS DTCs P0716 or P0717.
    • No OSS DTCs P0722 or P0723.
    • No TCC Stuck ON DTC P0742.
    • No Transmission Component Slipping DTC P0894.
    • No shift solenoid electrical DTCs P0973, P0974, P0976 or P0977.
    • The system voltage is 8-18 volts.
    • The engine run time is greater than 6 seconds.
    • The transmission OSS is 150 RPM or greater.
    • The transmission ISS is between 150 RPM and 6500 RPM.
    • Calc. throttle position is 8 percent or greater.
    • The engine torque is greater than 50 N·m (37 lb ft).
    • The transmission fluid temperature (TFT) is between 20°C and 130°C (68°F and 266°F).

Conditions for Setting the DTC

The following conditions both occur twice in one trip:

Condition 1

The TCM commands 1st gear and the gear ratio indicates 2nd gear, 1.44:1 to 1.50:1 for 2 seconds or greater.

Condition 2

The TCM commands 4th gear, and the gear ratio indicates 3rd gear, 0.98:1 to 1.03:1, and the TCC Duty Cycle is 55 percent or greater for 4 seconds or greater.

Action Taken When the DTC Sets
    • The TCM requests the engine control module (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.
    • The ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records.
    • The TCM stores the DTC P0751 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records.

Conditions for Clearing the MIL/DTC
    • The ECM turns OFF the MIL during the third consecutive trip in which the TCM does not send a MIL illumination request.
    • A scan tool can clear the MIL/DTC.
    • The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
    • The TCM 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 TCM.

Diagnostic Aids
    • Verify that the transmission meets the specifications in the Shift Speed table. Refer to Shift Speed .
    • Other internal transmission failures can cause more than one shift to occur.
    • 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.

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.

Step

Action

Value

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 ECM and TCM Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the ECM and 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 Testing for Intermittent Conditions and Poor Connections

3
  1. Inspect the shift solenoid/hydraulic circuit for the following conditions:
    2. • 1-2 shift solenoid mechanically stuck OFF
    •  Refer to Shift Solenoid Leak Test .
    • 1-2 shift valve stuck in the released position
    • Damaged seals on the 1-2 shift solenoid valves
    • Refer to Shift Solenoid Leak Test .
  2. Clean and inspect the related valves, bores and the valve body for debris or contamination restricting valve movement. Refer to Control Valve Body Cleaning and Inspection.

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. Operate the vehicle under the following conditions:
    4. • Drive the vehicle in D4.
    • Ensure that the gear ratios are as specified for 1st and 4th gear for 0.9 second or greater.
  4. Select Specific DTC.
  5. Enter DTC P0751.

Has the test run and passed?

1st: 2.42:1 to 2.52:1

4th: 0.70:1 to 0.80:1

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