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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Blazer - 2WD 🢒 Restraints 🢒 SIR 🢒 DTC P0751

Object Number: 42270 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics
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 four different shifting combinations.

When 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 TP sensor DTCs P0122 or P0123.
    • No VSS DTCs P0502 or P0503.
    • No TCC solenoid valve DTC P0740.
    • No TCC stuck ON DTC P0742.
    • No 1-2 SS valve DTC P0753.
    • No 2-3 SS valve DTC P0758.
    • No 3-2 SS valve assembly DTC P0785.
    • No TFP manual valve position switch DTC P1810.
    • No TCC PWM solenoid valve DTC P2761.
    • 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 greater than 10 percent.
    • 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.

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 1.2-1.825.
    • 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).
    • The PCM commands D2 line pressure.
    • The PCM inhibits 3-2 downshift if the vehicle speed is 48 km/h (30 mph) or greater.
    • The PCM freezes shift adapts from being updated.
    • 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.
    • Other internal transmission failures may cause more than one shift to occur.
    • Refer to the Shift Solenoid Valve State and Gear Ratio table.

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.

DTC P0751

Step

Action

Values

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

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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 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:

    • 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 .
    • Clean and inspect the related valves, bores and the valve body for debris or contamination restricting valve movement.
        Refer to Control Valve Body Disassemble in the 4L60-E section of the Transmission Unit Repair Manual.

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% 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