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For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Regal (China) (CNG) 🢒 Engine 🢒 Engine Controls - 3.0L (L46) 🢒 DTC P0751 1-2 Shift Solenoid Valve Performance

Object Number: 28126 Size: SF
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The 1-2, 3-4 shift solenoid (1-2, 3-4 SS) valve is fed ignition voltage by circuit 1039/839 and the ground path is provided by the PCM, depending on the solenoids commanded state. When the PCM commands the solenoid OFF, a ground path is not provided and the filtered line pressure that is fed to the solenoid is exhausted. When the PCM commands the solenoid ON, a ground path is provided and the exhaust port is blocked, stopping the exhaust of line pressure.

The PCM identifies a 1-2, 3-4 SS valve condition by monitoring the commanded gear versus gear ratio.

If the PCM detects a gear ratio that is outside its limits for a particular commanded gear, then DTC P0751 sets. DTC P0751 is a Type D DTC.

Conditions for Running the DTC
    • No TP sensor DTCs P0121, P0122 or P0123 are set.
    • No VSS DTCs P0502 or P0503 are set.
    • No A/T ISS sensor DTCs P0716 or P0717 are set.
    • No 1-2, 3-4 SS valve electrical DTC P0753 is set.
    • No 2-3 shift SS electrical DTC P0758 is set.
    • No TFP manual valve position switch DTC P1810 is set.
    • No TCC PWM solenoid valve DTC P1860 is set.
    • The engine speed is greater than 500 RPM for 5 seconds and not in fuel shut off.
    • The transmission is not in PARK or NEUTRAL.
    • The vehicle speed is greater than 8 km/h (5 mph).
    • The TP angle is greater than 10%.
    • The transmission fluid temperature is greater than 20°C (68°F).
    • The engine torque is 70-270 N·m (50-200 lb ft).

Conditions for Setting the DTC

DTC P0751 sets when one of the following cases occurs. The case must occur twice in one trip:

Case 1

    • The PCM commands 1st gear and the gear ratio indicates 2nd gear (1.52:1 to 1.62:1) for 2 seconds and;
    • The PCM commands 4th gear and the gear ratio indicates 3rd gear (0.95:1 to 1.05:1) for 3 seconds.

Case 2

    • The PCM commands 2nd gear and the gear ratio indicates 1st gear (2.87:1 to 2.97:1) for 3 seconds and;
    • The PCM commands 3rd gear and the gear ratio indicates 4th gear (0.65:1 to 0.75:1) for 3 seconds.

Action Taken When the DTC Sets
    • The PCM does not illuminate the malfunction indicator lamp (MIL).
    • The PCM commands maximum line pressure.
    • The PCM freezes shift adapts.
    • The PCM inhibits 3-2 downshifts when the vehicle speed is greater than 48 km/h (30 mph).
    • The PCM stores DTC P0751 in PCM history.

Conditions for Clearing the DTC
    • A scan tool clears the DTC from the PCM history.
    • The PCM clears the DTC from the PCM history if the vehicle completes 40 consecutive warm-up cycles without a 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
    • Inspect the transmission fluid for sediment.
    • Inspect the transmission filter for debris.
    • Ensure that the scan tool commanded gear has correct solenoid states and ratio.
        Refer to the Shift Solenoid Valve State and Gear Ratio table.

Test Description

Important: Do not drive the vehicle for an extended period of time because additional internal damage may occur.

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests that the PCM commanded all the shifts, that all the shift solenoid valves responded correctly, but that all the shifts did not occur.

DTC P0751 1-2, 3-4 Shift Solenoid Valve -- Performance

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check in Engine Controls

2

Was the transmission fluid checking procedure performed?

--

Go to Step 3

Go to Transmission Fluid Check

3

  1. Install the Scan Tool .
  2. Turn the ignition switch to the RUN position.

    3. Important: Before clearing the DTCs, use the Scan Tool in order to record the Freeze Frame and Failure Records for reference. Using the Clear Info function will erase the stored Freeze Frame and Failure Records from the PCM.

  3. Record the Freeze Frame and Failure Records.
  4. Clear the DTCs.
  5. Drive the vehicle in D4 range, under the following conditions:

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

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

--

Go to Step 4

Go to Diagnostic Aids

4

Inspect the 1-2, 3-4 shift solenoid valve/hydraulic circuit for the following conditions:

    • An internal malfunction.
    • Damaged seals on one or both of the shift solenoid valves.
        Refer to Shift Solenoid Leak Test .

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. Road test the vehicle in D4. Ensure that the transmission completes the 1-2, 2-3 and 3-4 upshifts with the TP angle at least 10%.
  4. Monitor TP angle, current gear and gear ratio on the Scan Tool . Ensure that the gear ratio values are correct for each gear, for at least 1 second per shift.
  5. Select Specific DTC.
  6. Enter DTC P0751.

Has the test run and passed?

1st: 2.87:1 to 2.97:1

2nd: 1.52:1 to 1.62:1

3rd: 0.95:1 to 1.05:1

4th: 0.65:1 to 0.75:1

System OK

Go to Step 1