GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 DTC 🢒 DTC P0756

Object Number: 42270 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

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

When the PCM detects a 4-3-3-4 shift pattern, then DTC P0756 sets. DTC P0756 is a type A DTC.

Conditions for Running the DTC
    • No TP sensor DTCs P0122 or P0123.
    • No VSS assembly DTCs P0502 or P0503.
    • No TCC solenoid valve DTC P0740.
    • No TCC stuck ON DTC P0742.
    • No 1-2 SS valve DTC P0753.
    • No 2-3 SS valve DTC P0758.
    • No 3-2 SS valve assembly DTC P0785.
    • No TFP manual valve position switch DTC P1810.
    • No TCC PWM solenoid valve DTC P1860.
    • The engine speed is greater than 450 RPM for 5 seconds.
    • The engine is not in fuel cutoff.
    • The gear range is D4.
    • The TP angle is greater than 10 percent.
    • The transmission fluid temperature is 20-130°C (68-266°F).
    • The system voltage is 10-18 volts.
    • The engine torque is 36-295 N·m (50-400 lb ft).
    • The transmission output speed is 150 RPM or greater.
    • The transfer case ratio in 4WD low is 0.9-1.2.
    • The transfer case ratio in 4WD high is 2.6-2.85.

Conditions for Setting the DTC

DTC P0756 sets if both of the following conditions occur:

Condition 1

    • The PCM commands first gear for 2 seconds.
    • The estimated gear ratio is 0 to 1.4.
    • All conditions are met for 1 second.

Condition 2

    • The PCM commands second gear for 1 second.
    • The estimated gear ratio is 0.9 to 1.2.
    • All conditions are met for 2 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL).
    • The PCM commands third gear only.
    • The PCM commands maximum line pressure.
    • The PCM inhibits TCC engagement.
    • The PCM freezes shift adapts from being updated.
    • The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame and Failure Records.
    • The PCM stores DTC P0756 in PCM history.

Conditions for Clearing the MIL/DTC
    • The PCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes.
    • A scan tool can clear the MIL/DTC.
    • The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission-related diagnostic fault occurring.
    • The PCM cancels the DTC default actions when the fault no longer exists and/or 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 more than one shift to occur.
    • Refer to the 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 that the PCM commanded all shifts, that all shift solenoid valves responded correctly, but that all the shifts did not occur.

DTC P0756

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain Diagnostic System Check?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls in Engine Controls - 4.3 L or Diagnostic System Check - Engine Controls in Engine Controls - 4.8 L, 5.3 L and 6.0 L

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, 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 DTC Freeze Frame and Failure Records.
  4. Clear the DTC.
  5. Drive the vehicle in D4 range under the following conditions:

    6. Accelerate the vehicle, ensuring that the PCM commands 1st, 2nd, 3rd and 4th gears.

Did you detect a 4-3-3-4 shift pattern?

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Go to Step 3

Go to Diagnostic Aids

3
  1. Inspect the shift solenoid/hydraulic circuit for the following conditions:
    2. • Debris or chips in the AFL oil passage.
    • Debris or chips restricting oil flow in passage #29 of the case or through the spacer plate gasket into the valve body.
    • A cracked 2-3 shift solenoid.
    • A 2-3 shift valve which is stuck or hung up in the valve body bore.
    • A 2-3 shuttle valve which is stuck or hung up in its bore.
    • Damaged seals on the shift solenoid valves.
    • Refer to Shift Solenoid Leak Test .
  2. Clean and inspect the related valves, bores and the valve body for debris or contamination.

Did you find and correct the condition?

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Go to Step 4

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4

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Info.
  3. Drive the vehicle in D4 range under the following condition, only if traffic and road conditions permit:

    4. Hold the throttle at 40% and accelerate to 64 km/h (40 mph).

  4. Select Specific DTC.
  5. Enter DTC P0756.

Has the test run and passed?

--

System OK

Go to Step 1