GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Sierra - 2WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E 🢒 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 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.

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 VSS DTCs P0502 or P0503.
    • No ISS DTCs P0716 or P0717.
    • No TCC Stuck On DTC P0742.
    • No TCC PWM electrical DTC P1860.
    • No TFP manual valve position switch DTC P1810.
    • The engine vacuum is 0-105 kPa.
    • No shift solenoid electrical DTCs P0753 or P0758.
    • No transmission component slipping DTC P1870.
    • The engine is running greater than 7 seconds.
    • The vehicle speed is greater than 11 km/h (7 mph).
    • 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).
    • Not in 4WD low.
    • The engine torque must be between 108 N·m (80 lb ft) and:
       - 6.0L: 542 N·m (400 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 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 operating conditions.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain Diagnostic System Check?

--

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 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 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.

    7. Refer to Transmission Fluid Pressure Manual Valve Position Switch Logic .

Does each selected transmission range match the scan tool TFP switch A/B/C display?

--

Go to Step 3

Go to DTC P1810

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. The vehicle may need to be road tested.

Was 1st gear commanded and not achieved, or 4th gear commanded and another gear occurred?

--

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.

Refer to Symptoms - Automatic Transmission .

Did you find and correct the condition?

--

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 gear for greater than one second in D1, D2, D3, and D4.
    • Accelerate the vehicle with the throttle angle greater than 7 percent up to 89 km/h (55 mph).
  4. Select Specific DTC.
  5. Enter DTC P0756.

Has the test run and passed?

--

System OK

Go to Step 1