GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2001 🢒 Yukon XL - 4WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 DTC P0751

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

Circuit Description

The 1-2 shift solenoid (SS) valve controls the fluid flow action on the 1-2 and the 3-4 shift valves. The 1-2 SS valve is a normally-open exhaust valve that is used with the 2-3 SS in order to allow four different shifting combinations.

When the powertrain control module (PCM) detects a 2-2-3-3 gear ratio, then DTC P0751 sets. DTC P0751 is a type C DTC. For California emissions vehicles and vehicles under 8600 GVW, DTC P0751 is a type B DTC.

Conditions for Running the DTC
    • No MAP sensor DTCs P0106, P0107, or P0108.
    • No TP sensor DTCs P0121, P0122, or P0123.
    • No AT ISS sensor DTCs P0716 or P0717.
    • No VSS DTCs P0502 or P0503.
    • No TFP manual valve position switch DTC P1810.
    • No TCC PWM solenoid valve DTC P1860.
    • No TCC Stuck-OFF DTC P0741.
    • The system voltage is 10.0-18.0 volts.
    • The engine must be running more than 400 RPM for 7 seconds.
    • The vehicle speed is greater than 3 km/h (2.0 mph).
    • The TP sensor is greater than 10 percent.
    • The engine torque must be between 108 N·m (80 lb ft) and:
       - 6.0 L: 576 N·m (425 lb ft)
       - 8.1 L: 881 N·m (650 lb ft)
    • No TFP manual valve position switch change within 6.0 seconds.
    • The TFP manual valve position switch indicates D4.
    • The transmission fluid temperature (TFT) is greater than 20°C (68°F) and less than 130°C (266°F).

Conditions for Setting the DTC
    • The commanded gear equals 1st and the ratio equals 2nd for greater than 2 seconds.
    • The commanded gear equals 4th with the TCC locked and the ratio equals 3rd for greater than 3.75 seconds.
    • All conditions are met for 2 occurrences.

Action Taken When the DTC Sets
    • For California emission equipped vehicles, the PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. For Non-California emission equipped vehicles, the MIL is not illuminated.
    • 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 (Calif. only) and Failure Records (Calif. and Federal).
    • The PCM stores the DTC P0751 in PCM history during the second consecutive trip (Calif.) or the first trip (Federal) in which the Conditions for Setting the DTC are met.

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.
    • Other internal transmission failures can cause more than one shift to occur. Refer to Shift Solenoid Valve State and Gear Ratio .
    • DTC P0751 defaults to an elevated line pressure condition which may result in TCC partial apply. This may induce idle surge and engine stall.

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 whether the scan tool commanded all the shifts, or whether all the shift solenoids responded correctly, but all of the correct shifts did not occur.

DTC P0751

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 (6.0 L) or Diagnostic System Check - Engine Controls (8.1 L) in Engine Controls

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 operating, 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 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 D4 range, use the scan tool in order to command FIRST, SECOND, THIRD, and FOURTH gears while accelerating the vehicle.

    4. The vehicle may need to be road tested.

Was a 2-2-3-3 shift pattern only detected?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the shift solenoid/hydraulic circuit for a 1-2 SS valve internal malfunction.
  2. Inspect the shift solenoid/hydraulic circuits for a stuck 1-2 or 3-4 shift valve.
  3. Inspect the shift solenoid/hydraulic circuit for damaged seals on one or both of the shift solenoids. The shift solenoids can cause oil to leak into the second gear clutch pack.

Refer to Symptoms - Automatic Transmission .

Did you find and correct the condition?

--

Go to Step 5

Go to Diagnostic Aids

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, if traffic and road conditions permit:
    4. • Accelerate the vehicle with the TP angle greater than 7% up to 89 km/h (55 mph).
    • The PCM must see the proper ratio for each commanded gear for greater than one second in D1, D2, D3, and D4. Wait for the TCC Lock-up in 4th gear.
  4. Select Specific DTC.
  5. Enter DTC P0751.

Has the test run and passed?

--

System OK

Go to Step 1