GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2003 🢒 Yukon XL - 2WD 🢒 DTC 🢒 DTC P0756

Object Number: 40795 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics

Circuit Description

The 2-3 shift solenoid (SS) valve controls fluid flow of 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.

When the powertrain control module (PCM) detects a 4-3-3-4 gear ratio, then DTC P0756 sets. DTC P0756 is a type C DTC. For California emissions vehicles and vehicles under 8,600 GVW, 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 AT VSS DTCs P0502 or P0503.
    • No AT ISS DTCs P0716 or P0717.
    • Not in 4WD low.
    • No TFP manual valve position switch DTC P1810.
    • No shift solenoid electrical DTCs P0753 or P0758.
    • No Transmission Component Slipping DTC P0894.
    • The transmission ISS is greater than 7 RPM.
    • No TCC Stuck ON DTC P0742.
    • No TCC PWM electrical DTC P1860.
    • The transmission OSS is greater than 7 RPM.
    • The system voltage is 10-18 volts.
    • The throttle angle is greater than 10 percent.
    • The transmission fluid temperature (TFT) is greater than 20°C (68°F) and less than 130°C (266°F).
    • The engine torque must be between 108 N·m (80 lb ft) and:
       - 6.0L: 576 N·m (425 lb ft)
       - 8.1L: 881 N·m (650 lb ft)

Conditions for Setting the DTC
    • The commanded gear is 1st and the ratio equals 4th for greater than 2.5 seconds.
    • The commanded gear is 2nd and the ratio equals 3rd for greater than 2.7 seconds.
    • All conditions are met for 2 occurrences.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) for California emissions vehicles.
    • The PCM commands a soft landing to 2nd gear.
    • The PCM commands maximum line pressure.
    • The PCM freezes shift adapts.
    • The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Freeze Frame, California only, and Failure Records, California and Federal.
    • The PCM stores DTC P0756 in PCM history.

Conditions for Clearing the MIL/DTC
    • For California emissions, 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.
    • For California emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without an emission related diagnostic fault occurring.
    • For Federal emissions, the PCM clears the DTC from PCM history if the vehicle completes 40 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. Refer to Shift Speed .
    • Other internal transmission failures may cause incorrect gear ratios to occur.
    • The customer may have concern of an engine over-rev condition or neutral condition in 4th gear. Refer to Shift Solenoid Valve State and Gear Ratio .
    • DTC P0756 defaults to an elevated line pressure condition which may result in partial TCC apply. This may produce an idle surge that could stall the engine.

Test Description

The number below refers to the step number 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.

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls in Engine Controls - 6.0L or Diagnostic System Check - Engine Controls in Engine Controls - 8.1L

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

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

--

Go to Step 3

Go to Intermittent Conditions in Engine Controls - 6.0L or Intermittent Conditions in Engine Controls - 8.1L

3
  1. Inspect the shift solenoid/hydraulic circuit for the following conditions:
    2. • 2-3 shift solenoid mechanically stuck ON
    • Refer to Shift Solenoid Leak Test .
    • 2-3 shift valve stuck in the applied position
    • A cracked 2-3 shift solenoid
    • 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 restricting oil flow.

    3. Refer to Control Valve Body Cleaning and Inspection in Transmission Unit Repair Manual.

Did you find and correct the condition?

--

Go to Step 4

--

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, holding the throttle at 40% and accelerating to 89 km/h (55 mph), only if traffic and road conditions permit.
  4. Select Specific DTC.
  5. Enter DTC P0756.

Has the test run and passed?

--

Go to Step 5

Go to Step 2

5

With the scan tool, observe the stored information, capture info and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 6.0L or Diagnostic Trouble Code (DTC) List in Engine Controls - 8.1L

System OK