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Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 DTC 🢒 DTC P0751 1-2 Shift Solenoid Valve Performance

DTC P0751 1-2 Shift Solenoid Valve Performance Diesel


Object Number: 40795 Size: MF
Automatic Transmission Components Gasoline
OBD II Symbol Description Notice

Circuit Description

The 1-2 Shift Solenoid Valve (1-2 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 Valve (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 Setting the DTC
    • No MAP Sensor DTCs P0106, P0107, or P0108
    • No OSS DTCs P0722 or P0723
    • No A/T ISS Sensor DTCs P0716 or P0717
    • No TCC DTCs P0741 or P0742.
    • No 1-2 SS Valve DTC P0753
    • No 2-3 SS Valve DTC P0758
    • No TFP Val. Position Sw. DTC P1810
    • The engine must be running greater than 475 RPM for at least 7 seconds.
    • The vehicle speed is greater than 3.2 km/h (2 mph).
    • The APP Angle is greater than 10%.
    • System voltage is 9.0-16.0 volts.
    • The Engine Torque is 108-644 N·m (80-475 lb ft).
    • The transmission fluid temperature is greater than 20°C (68°F) and less than 130°C (255°F).
    • The engine speed is less than 3750 RPM.
    • All the above conditions are met 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).
    • The PCM commands maximum line pressure.
    • The PCM freezes shift adapts.
    • DTC P0751 is stored in the PCM history.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL after three consecutive trips without a failure reported.
    • A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.
    • The PCM cancels the DTC default actions when the fault no longer exists and the ignition 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 Val. Position Sw.

    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.

P0751

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to A 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 for reference. Using the Clear Info function erases the stored Freeze Frame and Failure Records from the PCM.

  3. Record the DTC Freeze Frame and Failure Records, then clear the DTC.
  4. Select TFP Sw. A/B/C on the scan tool.
  5. With the engine operating, apply the brake pedal, and select each transmission range: D1, D2, D3, D4, N, R, and P.

Does each selected transmission range match the scan tool TFP Switch A/B/C display? (Refer to the Range Signal table.)

--

Go to Step 3

Go to DTC P1810 TFP Valve Position Switch Circuit

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.

Did you detect a 2-2-3-3 or 1-1-4-4 shift pattern only? (You may need to road test the vehicle).

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the shift solenoid/hydraulic circuit for a 1-2 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 the diagnosis tables.

Did you find and correct the condition?

--

Go to Step 5

--

5

In order to verify your repair, perform the following procedure:

  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. Enter DTC P0751.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1

DTC P0751 1-2 Shift Solenoid Valve Performance Gas


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

Circuit Description

The 1-2 Shift Solenoid Valve (1-2 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 Valve (2-3 SS Valve) in order to allow four different shifting combinations.

When the Vehicle Control Module (VCM) detects a 2-2-3-3 gear Ratio or a 1-1-4-4 gear ratio, then DTC P0751 sets. DTC P0751 is a type D DTC. For California emissions vehicles DTC P0751 is a type B DTC.

Conditions for Setting the DTC
    • No MAF DTCs P0101, P0102 or P0103.
    • No MAP Sensor DTCs P0106, P0107, or P0108.
    • No TP Sensor DTCs P0121, P0122, or P0123.
    • No OSS DTCs P0502 or P0503.
    • No A/T ISS Sensor DTCs P0716 or P0717.
    • No 1-2 SS Valve DTC P0753.
    • No 2-3 SS Valve DTC P0758.
    • No TFP Val. Position Sw. DTC P1810.
    • No TCC PWM Sol. Valve DTC P1860.
    • The engine must be running more than 475 RPM for 7 seconds.
    • The vehicle speed is greater than 3 km/h (2.0 mph).
    • The TP Sensor is greater than 10%. (5.7L), 12% (4.3L).
    • The Engine Torque is 95 N·m (70 lb ft) 4.3L, 108 N·m (80 lb ft) 5.7L, 7.4L to the following:
       - 405 N·m (300 lb ft) 4.3L
       - 540 N·m (400 lb ft) 5.7L
       - 675 N·m (500 lb ft) 7.4L.
    • The transmission fluid temperature (TFT) is greater than 20°C (68°F).
    • All the above conditions are met and one of the following conditions occur:

Stuck Off (after two occurrences)

When the 1-2 SS Valve is stuck OFF, first gear is commanded and the ratio is equal to second gear for greater than 2.0 seconds, and 4th gear is commanded with the TCC locked and the ratio equals 3rd gear for greater than 3 seconds.

Stuck On (after five occurrences 5.7L, 7.4L) (seven occurrences 4.3L)

When the 1-2 SS Valve is stuck ON, second gear is commanded and the ratio is equal to first gear for greater than 3 seconds.

Action Taken When the DTC Sets
    • The VCM illuminates the Malfunction Indicator Lamp (MIL) for California emissions vehicles.
    • The VCM commands maximum line pressure.
    • The VCM inhibits 3-2 downshifts above 25 mph.
    • The VCM freezes shift adapts.
    • DTC P0751 is stored in VCM history.

Conditions for Clearing the DTC
    • For California emissions only, the VCM turns OFF the MIL after three consecutive trips without a failure reported.
    • A scan tool can clear the DTC from the VCM history. The VCM clears the DTC from the VCM history if the vehicle completes 40 warm-up cycles without a failure reported.
    • The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

Diagnostic Aids
    • Verify that the transmission meets the specifications in the Shift Speed table.
    • Other internal transmission failures can cause more than one shift to occur.
    • First diagnose and clear any engine DTCs or TP 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 Val. Position Sw.

    2.

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

P0751

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 (4.3L) or

Powertrain On Board Diagnostic (OBD) System Check (5.7L) or Powertrain On Board Diagnostic (OBD) System Check (7.4L)

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 for reference. The Clear Info function erases the stored Freeze Frame and Failure Records from the VCM.

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

Does each selected transmission range match the scan tool TFP Switch display? (Refer to the Range Signal table.)

--

Go to Step 3

Go to DTC P1810 TFP Valve Position Switch Circuit

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.

Did you detect a 2-2-3-3 or 1-1-4-4 shift pattern only? (You may need to road test the vehicle).

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the shift solenoid/hydraulic circuit for a 1-2 SS Valve internal malfunction.
  2. Inspect the shift solenoid/hydraulic circuit for a stuck 1-2 shift valve.
  3. Inspect the shift solenoid/hydraulic circuit for damaged seals on one or both of the shift solenoids. The shift solenoids can leak oil into the second gear clutch pack.
  4. Refer to the diagnosis tables.

Did you find and correct the condition?

--

Go to Step 5

Refer to Diagnostic Aids

5

In order to verify your repair, perform the following procedure:

  1. Select DTC.
  2. Select Clear Info.
  3. Operate the vehicle under the following conditions (If traffic and road conditions permit):
    4. • Accelerate the vehicle with the TP angle greater than 12% up to 55 mph.
    • The VCM must see the proper ratio for each commanded gear for greater than one second in D1, D2, D3, and D4 (wait for the TCC Lock-up in 4th gear).
  4. Select Specific DTC. Enter DTC P0751.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1