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Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC Suburban - 4WD 🢒 DTC 🢒 DTC P0751 1-2 Shift Solenoid Valve Stuck Off

DTC P0751 1-2 Shift Solenoid Valve Stuck Off Diesel


Object Number: 40795 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics Diesel
OBD II Symbol Description Notice

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 shift solenoid (SS) valve 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 B DTC.

Conditions for Running the DTC
    • The system voltage is 8.0-18.0 volts.
    • The engine speed is greater than 475 RPM for greater than 7 seconds.
    • No OSS DTCs P0722 or P0723.
    • No ISS DTCs P0716 or P0717.
    • No TFP manual valve position switch DTC P1810.
    • TFP manual valve position switch indicates D4, D3, D2 or D1.
    • TFT is 20-130°C (68-266°F).
    • The APP angle is greater than 10%.
    • The vehicle speed is greater than 3.2 km/h (2 mph).
    • The engine torque is 140-675 N·m (100-500 lb ft).

Conditions for Setting the DTC
    • First gear is commanded with a ratio equal to second gear for greater than 1.5 seconds.
    • Fourth gear is commanded, with TCC applied or locked, with a ratio equal to third gear for greater than 3.5 seconds.
    • All conditions for running the DTC are met for 2 occurrences.

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 stores DTC P0751 in the PCM history.

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 clears the DTC from PCM history.
    • For Federal and California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 consecutive 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 consecutive 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.
    • Other internal transmission failures may cause similar shift patterns.
    • 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 table.

Test Description

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

  1. This step tests the function of the TFP manual valve position switch.

    2.

  2. This step tests whether the scan tool commanded all the shifts, or whether all the shift solenoids responded correctly, but all the shifts did not occur.

DTC P0751 (Diesel)

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Install the Scan Tool .
  2. With the engine OFF, turn the ignition switch to the RUN position.

    3. Important: Before clearing the DTCs, 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 Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Select TFP switch A/B/C on the scan tool.
  6. With the engine operating, apply the brake pedal, and select each transmission range: D1, D2, D3, D4, N, R, and P.

Refer to the Range Signal table.

Does each selected transmission range match the scan tool TFP switch A/B/C display?

--

Go to Step 3

Go to DTC P1810 TFP Valve Position Switch Invalid Range

3

  1. Raise and support the drive axle assembly.
  2. Start the engine.
  3. With the transmission in D4 range, use the scan tool in order to command first, second, third, and fourth gears while accelerating the vehicle.

Was a 2-2-3-3 shift pattern detected? (You may need to road test the vehicle).

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the shift solenoid/hydraulic circuits for a 1-2 or 3-4 SS valve internal malfunction.
  2. Inspect the shift solenoid/hydraulic circuit for damaged seals on one or both of the shift solenoids.
  3. Refer to Symptom Diagnosis .

Was the condition corrected?

--

Go to Step 5

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5

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 (if traffic and road conditions permit):
    4. • Place the transmission in D4.
    • Hold the throttle greater than 10%, and accelerate to 55 mph.
    • The PCM must see the proper gear ratio for each commanded gear, for greater than one second in D1, D2, D3, and D4 with TCC locked.
  4. Select Specific DTC.
  5. Enter DTC P0751.

Has the test run and passed?

--

System OK

Go to Step 1