GM Service Manual Online
For 1990-2009 cars only

Diagnostic Instructions

    • Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
    • Review Strategy Based Diagnosis for an overview of the diagnostic approach.
    •  Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0751: 1-2 Shift solenoid (SS) Valve Performance - No First or Fourth Gear

DTC P0752: 1-2 Shift solenoid (SS) Valve Performance - No Second or Third Gear

Diagnostic Fault Information

Hydraulic Circuit

Short to Ground

Open/High Resistance

Short to Voltage

Signal Performance

1-2 SS Valve

--

--

--

P0751, P0752

2-3 SS Valve

--

--

--

P0756, P0757

TCC PWM Valve

--

--

--

P0741, P0742

Typical Scan Tool Data

1-2 Shift solenoid (SS) Valve Performance Parameter Data

Circuit

Normal

Short to Ground

Open/High Resistance

Short to Voltage

Operating Conditions: Engine running, normal operating temperature

Parameter Normal Range: OK

1-2 Sol. CKT Status

OK

Open/Short to GND

Open/Short to GND

Short to Volts

2-3 Sol. CKT Status

OK

Open/Short to GND

Open/Short to GND

Short to Volts

TCC Duty Cycle CKT Status

OK

Open/Short to GND

Open/Short to GND

Short to Volts

Circuit/System Description

The 1-2 shift solenoid (SS) valve and the 2-3 SS valve are supplied with fused ignition voltage. The ground path is controlled by the transmission control module (TCM). When the TCM 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 TCM commands the solenoid ON, a ground path is provided and the exhaust port is blocked, stopping the exhaust of line pressure. The TCM identifies a 1-2 SS valve or a 2-3 SS valve condition by monitoring the commanded gear versus gear ratio. Refer to Shift Solenoid Valve State and Gear Ratio .

Conditions for Running the DTC

P0751

    • No TP sensor DTCs P0121, P0122, or P0123.
    • No ISS DTCs P0716 or P0717.
    • No OSS DTCs P0722 or P0723.
    • No TCC system stuck ON DTC P0742.
    • No 1-2 SS valve electrical DTCs P0973 or P0974.
    • No 2-3 SS valve electrical DTCs P0976 or P0977.
    • The calc. throttle position is 8 percent or more.
    • The transmission ISS is 150 RPM or more.
    • The transmission OSS is 200 RPM or more.
    • The time since the last gear change is 1 second.
    • The engine speed is greater than 500 RPM for 5 seconds.
    • The transmission fluid temperature is between 20-130°C (68-266°F).
    • The engine torque is greater than 50 N·m (37 lb ft).

P0752

    • No TP sensor DTCs P0121, P0122, or P0123.
    • No ISS DTCs P0716 or P0717.
    • No OSS DTCs P0722 or P0723.
    • No TCC system stuck ON DTC P0742.
    • No 1-2 SS valve electrical DTCs P0973 or P0974.
    • No 2-3 SS valve electrical DTCs P0976 or P0977.
    • The calc. throttle position is 8 percent or more.
    • The transmission ISS is 150 RPM or more.
    • The transmission OSS is 200 RPM or more.
    • The engine torque is greater than 50 N·m (37 lb ft).
    • The time since the last gear change is 1 second.
    • The engine speed is greater than 500 RPM for 5 seconds.
    • The transmission fluid temperature is between 20-130°C (68-266°F).

Conditions for Setting the DTC

P0751

The following conditions both occur twice in one trip:

P0751 - Condition 1

The TCM commands 1st gear and the gear ratio indicates 2nd gear, 1.54:1 to 1.71:1. for 2 seconds.

P0751 - Condition 2

The TCM commands 4th gear and the gear ratio indicates 3rd gear, 0.95:1 to 1.05:1, for 4 seconds.

P0752

The following conditions both occur twice in one trip:

P0752 - Condition 1

The TCM commands 2nd gear and the gear ratio indicates 1st gear, 2.81:1 to 3.11:1 for 2 seconds.

P0752 - Condition 2

The TCM commands 3rd gear and the gear ratio indicates 4th gear, 0.65:1 to 0.72:1, for 3 seconds.

Action Taken When the DTC Sets

P0751

    • DTC P0751 is a Type B DTC.
    • The TCM commands maximum line pressure.
    • The TCM freezes transmission adaptive functions.

P0752

    • DTC P0752 is a Type B DTC.
    • The TCM inhibits 3-2 downshifts when the vehicle speed is greater than 52 km/h (32 mph).
    • The TCM forces the TCC ON.
    • The TCM commands maximum line pressure.
    • The TCM freezes transmission adaptive functions.

Conditions for Clearing the DTC

DTCs P0751 and P0752 are Type B DTCs.

Diagnostic Aids

If the DTC is cleared, then will not reset when the vehicle is driven, some of the following conditions may exist:

    • Fluid contamination
    • Plugged fluid circuits
    • Restricted fluid circuits
    • Inspect transmission fluid lines to radiator. Lines may be pinched, plugged or twisted.
    • Refer to Shift Solenoid Valve State and Gear Ratio .
    • Internal damage to the torque converter may prevent TCC application.
    • It is possible for an internal TCM failure which may not allow sufficient current to operate the solenoids. Verify TCM functionality by commanding the suspected solenoid ON/OFF using the scan tool and listen for a click.

Reference Information

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

    •  Circuit Testing
    •  Connector Repairs
    •  Testing for Intermittent Conditions and Poor Connections
    •  Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

  1. Perform the Transmission Fluid Check to verify correct fluid level and condition. The transmission fluid level should be within the crosshatch band and the transmission fluid should be red or dark brown.
  2. If the transmission fluid is low or discolored, refer to Automatic Transmission Fluid Filter and Seal Replacement .
  3. Operate the vehicle in Drive and ensure that the TCM commands all gears. The ratios should match the commanded gear for all gears. Refer to Shift Solenoid Valve State and Gear Ratio .
  4. If the gear ratios do not match the commanded gear, inspect the following and repair/replace as necessary:
    • Inspect the shift solenoid/hydraulic circuit for an internal malfunction.
    • Damaged seals on the shift solenoid valve. Refer to Shift Solenoid Leak Test for further diagnosis.
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

    •  Shift Solenoid Leak Test
    •  1-2 Shift Solenoid Valve Replacement
    •  Control Valve Body Disassemble
    •  Control Valve Body Cover Removal and Side Cover/Gaskets, Disassemble, Assemble, Install