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Makes 🢒 GMC_Truck 🢒 1999 🢒 GMC Suburban - 2WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E 🢒 DTC P0756 2-3 Shift Solenoid Valve Performance

DTC P0756 2-3 Shift Solenoid Valve Performance Gas


Object Number: 40795 Size: MF

Circuit Description

The 2-3 shift solenoid (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 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 Running the DTC
    • No MAF sensor 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 ISS DTCs P0716 or P0717.
    • No 4WD low DTC P1875.
    • Not in 4WD low.
    • No TFP manual valve position switch 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

Conditions for Setting the DTC

All conditions for running the DTC are met, and either of the two following conditions occur:

Stuck On (for 2 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 3 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.
    • The VCM stores DTC P0756 in VCM history.

Conditions for Clearing the MIL/DTC
    • For California emissions, the VCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
    • A scan tool clears the DTC from VCM history.
    • For California emissions, the VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without an emission related diagnostic fault occurring.
    • For Federal emissions, the VCM clears the DTC from VCM history if the vehicle completes 40 consecutive warm-up cycles without a non-emission related diagnostic fault occurring.
    • The VCM 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 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 valve position switch.

    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. Using the Clear Info function erases the Freeze Frame and Failure Records from the VCM.

  3. Record the Freeze Frame and Failure Records.
  4. Clear the DTCs.
  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 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 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 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% up to 55 mph. The TCC must be locked in FOURTH gear.
  4. Select Specific DTC.
  5. Enter DTC P0756.

Has the test run and passed?

--

System OK

Go to Step 1