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Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC Suburban - 2WD 🢒 DTC 🢒 DTC P0756 2-3 Shift Solenoid Valve Performance

DTC P0756 2-3 Shift Solenoid Valve Performance Gas


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

Circuit Description

The 2-3 Shift Solenoid Valve (2-3 SS Valve) controls fluid flow acting on the 2-3 shift valves. The 2-3 SS Valve is a normally-open exhaust valve used with the 1-2 Shift Solenoid Valve (1-2 SS Valve) in order to allow for four different shift combinations.

If the VCM detects a non first gear ratio while first gear is commanded, or a first gear ratio while fourth gear is commanded, then DTC P0756 sets. DTC P0756 is a type D DTC. For California emissions vehicles, DTC P0756 is a type A DTC.

Conditions for Setting the DTC
    • No MAF DTCs P0101, P0102 or P0103.
    • No MAP 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 4WD Low DTC P1875.
    • Not in 4WD Low.
    • No TFP Val. Position Sw. DTC P1810.
    • No shift solenoid electrical DTCs P0753 or P0758.
    • The engine runs more than 475 RPM for 7 seconds.
    • The vehicle speed is greater than 4 km/h (2.0 mph).
    • The TP Angle is greater than 8%.
    • The transmission fluid temperature (TFT) is greater than 20°C (68°F).
    • The engine torque is 108 N·m (80 lb ft) to the following:
       - 540 N·m (400 lb ft) 5.7L
       - 675 N·m (500 lb ft) 7.4L.
    • All of the above conditions are met and either of the two following conditions occur:

Stuck On (for 7 occurrences)

When the 2-3 SS Valve is stuck on, the commanded gear equals 1st and the ratio equals 4th for greater than 2 seconds, and the commanded gear equals 2nd and the ratio equals 3rd for greater than 3 seconds.

Stuck Off (for 7 occurrences)

When the 2-3 SS Valve is stuck off, the commanded gear equals 3rd and the ratio equals 2nd for greater than 4 seconds.

Action Taken When the DTC Sets
    • The VCM illuminates the Malfunction Indicator Lamp (MIL) for California emissions vehicles.
    • The transmission immediately lands to 2nd gear.
    • The VCM commands maximum line pressure.
    • The VCM freezes shift adapts.
    • DTC P0756 is stored in VCM history.

Conditions for Clearing the MIL/DTC
    • For California emissions vehicles, 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 may cause more than one shift to occur.
    • The customer may complain of an engine over-rev condition or neutral condition in 4th gear.
    • 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 for a selected gear ratio versus a ratio not obtainable under normal operating conditions.

P0756

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 (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 will erase 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 running, 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 the D4 range, use the scan tool in order to command 1st, 2nd, 3rd, and 4th gears while accelerating the vehicle.

Was 1st gear commanded and not achieved, or 4th gear commanded and another gear occurred? (You may need to road test the vehicle).

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the shift solenoid/hydraulic for an internal malfunction at one or both of the shift solenoids.
  2. Inspect the shift solenoid/hydraulic 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 only if traffic conditions permit:
    4. • The VCM must see the proper gear ratio for each gear for greater than one second in D1, D2, D3, and D4.
    • Accelerate the vehicle with the TP angle greater than 8% (4.3L, 12.5%) up to 55 mph. The TCC must be locked in fourth gear.
  4. Select Specific DTC. Enter DTC P0756.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1

DTC P0756 2-3 Shift Solenoid Valve Performance Diesel


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

Circuit Description

The 2-3 Shift Solenoid Valve (2-3 SS Valve) controls fluid flow acting on the 2-3 shift valve. The 2-3 SS Valve is a normally-open exhaust valve that is used with the 1-2 Shift Solenoid Valve (1-2 SS Valve) to allow four different shift combinations.

When the Powertrain Control Module (PCM) detects a non first gear ratio while first gear is commanded or a first gear ratio while fourth gear is commanded, then DTC P0756 sets. DTC P0756 is a type A DTC.

Conditions for Setting the DTC
    • No TFT Sensor DTCs P0712 or P0713
    • No A/T ISS Sensor DTCs P0716 or P0717
    • No OSS Sensor DTCs P0722 or P0723
    • No shift solenoid electrical DTCs P0753 or P0758
    • No TFP Val. Position Sw. DTC P1810
    • No 4WD Lo DTC P1875
    • System voltage is 9.0-16.0 volts.
    • Not in 4WD Low
    • The vehicle speed is greater than 3.2 km/h (2 mph).
    • The APP angle is greater than 10%.
    • The Transmission Fluid Temperature (TFT) is 20°-130°C (68°-266°F).
    • The engine torque is 100-644 N·m (80-475 lb ft).
    • The engine speed is 475-3750 RPM for at least 7 seconds.
    • All of the above conditions are met and either of the two following conditions occur:

Stuck On (after 2 occurrences)

   • 

First gear is commanded and the ratio equals 4th gear for greater than 2.75 seconds.

   • 

Second gear is commanded and the gear ratio equals 3rd for greater than 2.75 seconds.

Stuck Off (after 7 Occurrences)

Third gear is commanded and the gear ratio equals 2nd for greater than 3.25 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the Malfunction Indicator Lamp (MIL).
    • The PCM commands 2nd gear.
    • The PCM commands maximum line pressure.
    • The PCM freezes shift adapts.
    • DTC P0756 is stored in 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.
    • The customer may complain of an engine over-rev condition or neutral condition in 4th gear.
    • 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 for a selected gear ratio versus a ratio not obtainable under normal driving conditions.

P0756

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 for reference. Using the Clear Info function will erase 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 running, 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 the D4 range, use the scan tool in order to command 1st, 2nd, 3rd, and 4th gears while accelerating the vehicle.

Was 1st gear commanded and not achieved, or 4th gear commanded and another gear occurred? (You may need to road test the vehicle).

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the shift solenoid/hydraulic for an internal malfunction at one or both of the shift solenoids.
  2. Inspect the shift solenoid/hydraulic 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 only if traffic conditions permit:
    4. • 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.
    • Accelerate the vehicle with the TP greater than 10% to 55 mph.
  4. Select Specific DTC. Enter DTC P0756.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1