GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2002 🢒 Chevy C Cab/Chassis HD (GMT 400) 🢒 DTC 🢒 DTC P0751

DTC P0751 Gas


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

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 DTC P0751 is a type B 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 P1120 or P1220.
    • No VSS DTCs P0502 or P0503.
    • No ISS sensor DTCs P0716 or P0717.
    • No shift solenoid electrical DTC P0758 or P0753.
    • No TFP manual valve position switch DTC P1810.
    • No transmission component slipping DTC P1870.
    • No TCC solenoid valve DTC P1860.
    • No TCC stuck on DTC P0742.
    • The system voltage is 10-18 volts.
    • The engine must be running for 7 seconds.
    • The vehicle speed is greater than 3 km/h (2 mph).
    • The TP sensor is greater than 10 percent.
    • The engine torque is 108 N·m (80 lb ft) to 881 N·m (650 lb ft).
    • No TFP manual valve position switch change within 6 seconds.
    • The commanded gear is not 1st.
    • The TFP manual valve position switch indicates D4.
    • The transmission fluid temperature (TFT) is 20-130°C (68-266°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 Federal 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, California only, and Failure Records, California and Federal.
    • The PCM stores the DTC P0751 in PCM history during the second consecutive trip, California, 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
    • DTC P0751 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 ratios to occur.
    • 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 whether the scan tool can command the shift solenoids correctly, but not all of the shifts occurred.

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 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 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 Shift Transmission function in order to command FIRST, SECOND, THIRD, and FOURTH gears while accelerating the vehicle. 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 1-2 shift solenoid/hydraulic circuit for an internal malfunction.
  2. Inspect the 1-2 or 3-4 shift solenoid/hydraulic circuits for a stuck 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 throttle angle greater than 7 percent up to 89 km/h (55 mph).
    • The PCM must see the correct ratio for each commanded gear for greater than one second. 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

DTC P0751 Diesel


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

Circuit Description

The 1-2 shift solenoid (SS) valve controls the fluid flow 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 valve to allow four different shifting combinations.

When the powertrain control module (PCM) detects a 2-2-3-3 or a 1-1-4-4 gear ratio, then DTC P0751 sets. DTC P0751 is a type B DTC.

Conditions for Running the DTC
    • No MAP sensor DTCs P0106, P0107, or P0108.
    • No VSS DTCs P0722 or P0723.
    • No ISS sensor DTCs P0716 or P0717.
    • No TCC DTCs P0741 or P0742.
    • No 1-2 shift solenoid valve DTC P0753.
    • No 2-3 shift solenoid valve DTC P0758.
    • No TFP manual valve position switch DTC P1810.
    • No TCC P1860.
    • The engine must be running for at least 7 seconds.
    • The vehicle speed is greater than 3 km/h (2 mph).
    • The APP angle is greater than 10 percent.
    • System voltage is 8-18 volts.
    • The engine torque is 108-644 N·m (80-475 lb ft).
    • The transmission fluid temperature (TFT) is greater than 20°C (68°F) and less than 130°C (255°F).
    • The engine speed is less than 3,750 RPM.

Conditions for Setting the DTC

All the above conditions are met for Running the DTC and one of the following conditions occur:

Stuck Off - for two occurrences

    •  First gear is commanded and the gear ratio is equal to second gear for greater than 1.5 seconds.
    • Fourth gear is commanded, with TCC locked, and the gear ratio equals third gear for greater than 3 seconds.

Stuck On - for five occurrences

Second gear is commanded and the gear ratio equals first gear for greater than 2.2 seconds.

Action Taken When the DTC Sets
    • The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.
    • 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 the DTC P0751 in PCM history during the second consecutive trip in which the Conditions for Setting the DTC are met.

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
    • First diagnose and clear any engine DTCs or APP Sensor codes that are present. Then inspect for any transmission DTCs that may have reset. Refer to Shift Solenoid Valve State and Gear Ratio table.
    • DTC P0751 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 ratios to occur.

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 can command the shift solenoids correctly, but not all the shifts occurred.

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

    4. Road testing the vehicle may be necessary.

Was a 2-2-3-3 or 1-1-4-4 shift pattern only detected?

--

Go to Step 4

Go to Diagnostic Aids

4
  1. Inspect the 1-2 shift solenoid/hydraulic circuit for an 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.

    4. 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, if traffic and road conditions permit:
    4. • Place the transmission in D4.
    • Hold the throttle greater than 10 percent, and accelerate to 89 km/h (55 mph).
    • The PCM must see the correct gear ratio for each commanded gear for greater than one second. 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