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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2002 🢒 GMC C Cab/Chassis HD (GMT 400) 🢒 DTC 🢒 DTC P0756

DTC P0756 Gas


Object Number: 40795 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics L18

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.

If the powertrain control module (PCM) 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 C 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 VSS DTCs P0502 or P0503.
    • No ISS DTCs P0716 or P0717.
    • No TCC stuck ON DTC P0742.
    • No 4WD low DTC P1875.
    • No transmission component slipping DTC P1870.
    • Not in 4WD low.
    • No TFP manual valve position switch DTC P1810.
    • No shift solenoid electrical DTCs P0753 or P0758.
    • The engine is running for 7 seconds.
    • The vehicle speed is greater than 4 km/h (2 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).
    • The engine torque is 108 N·m (80 lb ft) to 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
    • 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.
    • Verify that the transmission meets the specifications in the Shift Speed table.
    • Other internal transmission failures may cause incorrect gear ratio to occur.
    • The customer may complain of an engine over-rev condition or neutral condition in 4th gear.
    • Refer to Shift Solenoid Valve State and Gear Ratio .

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.

DTC P0756

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 - 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.

Refer to Shift Solenoid Valve State and Gear Ratio .

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 correct ratio for each commanded gear for greater than one second.
    • 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

DTC P0756 Diesel


Object Number: 40795 Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics L65

Circuit Description

The 2-3 shift solenoid (SS) valve controls fluid flow of the 2-3 shift valve. The 2-3 SS valve is a normally-open exhaust valve that is used with the 1-2 SS valve to allow four different shift combinations.

When the powertrain control module (PCM) 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 A DTC.

Conditions for Running the DTC
    • No ISS sensor DTCs P0716 or P0717.
    • No VSS sensor DTCs P0722 or P0723.
    • No shift solenoid electrical DTCs P0753 or P0758.
    • No TFP manual valve position switch DTC P1810.
    • System voltage is 8-18 volts.
    • The vehicle speed is greater than 3 km/h (2 mph).
    • The APP angle is greater than 10 percent.
    • The transmission fluid temperature (TFT) is 20-130°C (68-266°F).
    • The engine torque is 100-644 N·m (80-475 lb ft).
    • The engine speed is 475-3,750 RPM for at least 7 seconds.

Conditions for Setting the DTC

All of the above Conditions for Running the DTC are met and either of the two following conditions occur:

Stuck On - after 2 occurrences

    • First gear is commanded and the ratio equals 4th gear for greater than 2.75 seconds.
    • Second gear is commanded and the gear ratio equals 3rd for greater than 2.75 seconds.

Stuck Off - after 7 occurrences

Third gear is commanded and the gear ratio equals 2nd for greater than 2.75 seconds.

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 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
    • 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 can clear the MIL/DTC.
    • For Federal and 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 vehicles equal to or greater than 15,000 lbs GVW, 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
    • 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.
    • 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.

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.

P0756

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 - 6.5L

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. 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.

    4. Road testing the vehicle may be necessary.

Refer to Shift Solenoid Valve State and Gear Ratio .

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 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 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 correct ratio for each commanded gear for greater than one second in D1, D2, D3, and D4 with TCC locked.
    • Accelerate the vehicle with the throttle greater than 10 percent 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