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Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC Suburban - 2WD 🢒 DTC 🢒 DTC P0756 2-3 Shift Solenoid Valve Stuck On

DTC P0756 2-3 Shift Solenoid Valve Stuck On 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 (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 (SS) valve to allow four different shift combinations.

When the powertrain control module (PCM) detects a 4-3-3-4 gear ratio, then DTC P0756 sets. DTC P0756 is a type A 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 (68-265°F).
    • The APP angle is greater than 10%.
    • The vehicle speed is greater than 3.2 km/h (2 mph).
    • The engine torque is 225-675 N·m (166-500 lb ft).

Conditions for Setting the DTC
    • First gear is commanded with a ratio equal to fourth gear for greater than 2.8 seconds.
    • Second gear is commanded with a ratio equal to third gear for greater than 2.8 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 2nd gear.
    • The PCM commands maximum line pressure.
    • The PCM freezes shift adapts.
    • The PCM stores DTC P0756 in 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.
    • 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 manual valve position switch.

    2.

  2. This step tests for a selected gear ratio versus a ratio not obtainable under normal driving conditions.

DTC P0756 (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 running, 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 the D4 range, use the scan tool in order to command 1st, 2nd, 3rd, and 4th gears while accelerating the vehicle.

It may be necessary to road test the vehicle.

Was a 4-3-3-4 shift pattern detected?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the shift solenoid/hydraulic circuits for an internal malfunction at one or both of the shift solenoids.
  2. Inspect the shift solenoid/hydraulic circuits for damaged seals on one or both of the shift solenoids.

    3. Refer to Symptom Diagnosis .

Was the condition corrected?

--

Go to Step 5

--

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 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.
  5. Enter DTC P0756.

Has the test run and passed?

--

System OK

Go to Step 1