DTC P0751 1-2 Shift Solenoid Valve Performance. Buick Park Avenue 1998

For 1990-2009 cars only

Makes 🢒 Buick 🢒 1998 🢒 Park Avenue 🢒 DTC 🢒 DTC P0751 1-2 Shift Solenoid Valve Performance

Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The 1-2 Shift Solenoid is fed ignition voltage by circuit 639 and the ground path is provided by the Powertrain Control Module (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 Powertrain Control Module (PCM) identifies a 1-2 Shift Solenoid Valve (1-2 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 B DTC.

Conditions for Setting the DTC

•	No TP Sensor DTCs P0121, P0122 or P0123 are set.

•	No VSS DTCs P0502 or P0503 are set.

•	No A/T ISS DTCs P0716 or P0717 are set.

•	No 1-2 shift solenoid valve electrical DTC P0753 is set.

•	No 2-3 shift solenoid valve electrical DTC P0758 is set.

•	No TCC PWM Sol. DTC P1860 is set.

•	No TFP Sw. DTC P1810 is set.

•	The engine speed is greater than 500 RPM for 5 seconds, and not in fuel shut off mode.

•	The vehicle speed is greater than 8 km/h (5 mph).

•	The throttle angle is greater than 10%.

•	The transmission fluid temperature is greater than 20°C (68°F).

•	The transmission is not in Park/Neutral.

•	The engine torque is 70-270 N·m (50-200 lb ft).

All of the above conditions are met and cases 1 and 4 are true twice, or cases 2 and 3 are true twice.

Case 1

•	First gear is commanded.

•	The gear ratio indicates second gear (1.52:1 to 1.62:1).

•	Condition is met for 2 seconds.

Case 2

•	Second gear is commanded.

•	The gear ratio indicates first gear (2.87:1 to 2.97:1).

•	Condition is met for 3 seconds.

Case 3

•	Third gear is commanded.

•	The gear ratio indicates fourth gear (0.65:1 to 0.75:1).

•	Condition is met for 3 seconds.

Case 4

•	Fourth gear is commanded.

•	The gear ratio indicates third gear (0.95:1 to 1.05:1).

•	Condition is met for 3 seconds.

Action Taken When the DTC Sets

•	The PCM illuminates the Malfunction Indicator Lamp (MIL).

•	The PCM commands maximum line pressure.

•	The PCM disables shift adapts.

•	The PCM inhibits 3-2 downshifts when the vehicle speed is greater than 48 km/h (30 mph).

Conditions for Clearing the MIL/DTC

•	The PCM turns OFF the MIL after three consecutive trips without a failure reported.

•	A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

•	The PCM cancels the DTC default actions when the fault no longer exists and the ignition 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 Shift Solenoid Valve State and Gear Ratio .

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.

Set up data pairs (current gear and gear ratio) on the Scan Tool . Drive the vehicle while commanding First gear with the Scan Tool .

This step verifies that the gear ratio indicated a Second gear start and the vehicle does not achieve First gear. The list of components should be inspected and repaired if faulty.

This step verifies that the gear ratio indicates Third gear and the vehicle does not achieve Fourth gear. The list of components should be inspected and repaired if faulty.

This step verifies that the gear ratio indicates First gear and the vehicle does not achieve Second gear. The list of components should be inspected and repaired if faulty.

This step verifies that the gear ratio indicates Fourth gear and the vehicle does not achieve Third gear. The list of components should be inspected and repaired if faulty.

DTC P0751 1-2 Shift Solenoid Valve -- Performance

Step

Action

Value(s)

Yes

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

Have you performed the transmission fluid checking procedure?

Go to Step 3

Go to Transmission Fluid Check

Install the Scan Tool .
With the engine OFF, turn the ignition switch to the RUN position.

Important: Before clearing the DTCs, use the Scan Tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

Record the DTC Freeze Frame and Failure Records, then clear the DTC(s).
Select A/T Output, then select Shift Trans.
Monitor the Current gear and Gear ratio data parameters:
Accelerate the vehicle and command First gear.

Is the gear ratio within the specified values?

1.52:1 to 1.62:1

Go to Step 4

Go to Step 5

Inspect for the following conditions:

•	A damaged Lo/Rev servo apply pin

•	The 1-2 shift valve is stuck in upshifted position, or the valve contains debris

•	The FWD/CC support seals are damaged

•	The FWD/CC studs are damaged or broken

•	The Lo roller clutch is worn or damaged

•	The Forward clutch piston is damaged or cracked

•	The Forward clutch piston seals are rolled, cut or damaged

•	The Support housing seal rings are leaking, damaged or cut

•	The Forward sprag is damaged or not holding

•	The ball check valves are missing or stuck

Repair or replace any malfunctioning components.

Refer to Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual.

Have you completed the inspection and repair?

Go to Step 11

Accelerate the vehicle and command a 3-4 shift.

Is the gear ratio within the specified parameters?

0.95:1 to 1.05:1

Go to Step 6

Go to Step 7

Inspect for the following conditions:

•	The 1-2 shift solenoid valve is stuck in the ON position or the valve contains debris.

•	The Fourth band is burned or slipping

•	The Fourth servo pin is broken or seized

•	The Fourth servo piston is damaged

•	The Fourth servo seals are rolled, cut or damaged

•	The Fourth servo cover is cracked

•	The 3-4 shift valve bore plug is misassembled

Repair or replace any malfunctioning components.

Refer to Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual.

Is the inspection and repair complete?

Go to Step 11

Accelerate the vehicle and command a 1-2 shift.

Is the gear ratio within the specified parameters?

2.87:1 to 2.97:1

Go to Step 8

Go to Step 9

Inspect for the following conditions:

•	The 1-2 shift solenoid valve is stuck in the ON position or the valve contains debris.

•	The 1-2 shift valve is stuck in 1st gear or the valve contains debris.

•	The Clutch plates are burned or damaged

•	The Piston assembly in 2nd clutch is cracked or damaged

•	The 2nd clutch return spring is broken or out of position

•	The Piston seals on the 2nd clutch piston are rolled, damaged or leaking

•	The 2nd sprag is not holding or is damaged

Repair or replace any malfunctioning components.

Refer to Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual.

Is the inspection and repair complete?

Go to Step 11

Accelerate the vehicle and command a 2-3 shift.

Is the gear ratio within the specified parameters?

0.65:1 to 0.75:1

Go to Step 10

Go to Diagnostic Aids

Inspect for the following conditions:

•	The 1-2 shift solenoid valve is stuck in the OFF position or the valve contains debris.

•	The exhaust valve cup plug for the driven sprocket support or valve is improperly installed.

•	The third clutch plates are burned or contain damaged splines

•	The third clutch piston is cracked or damaged, or the piston contains ball check valve damage

•	The third clutch seals on piston are rolled, damaged or leaking

•	The ball check valve is missing or stuck

Repair or replace any malfunctioning components.

Refer to Transmission Overhaul in the 4T65-E Section of the Transmission Unit Repair Manual.

Is the inspection and repair complete?

Go to Step 11

In order to verify your repair, perform the following procedure:

Select DTC.
Select Clear Info, then clear the DTC(s).
Operate the vehicle under the following conditions:

•	The transmission fluid temperature is greater than 20°C (68°F).

•	The engine speed is more than 500 RPM for 5 seconds.

•	Not in fuel shut off.

•	The throttle position is greater than 10%.

•	The gear range is not in Park/Neutral.

•	The vehicle sped is more than 8 km/h (5 mph).

•	The engine torque is 70-270 N·m (50-200 lb ft).

•	Each of the following pass criteria must be true for 1 second:

Case 1

-	Command 1st gear.

-	The gear ratio is 2.87:1 to 2.97:1.

Case 2

-	Command 2nd gear.

-	The gear ratio is 1.52:1 to 1.62:1.

Case 3

-	Command 3rd gear.

-	The gear ratio is 0.95:1 to 1.05:1

Case 4

-	Command 4th gear.

-	The gear ratio is 0.65:1 to 0.75:1.

Select Specific DTC.
Enter DTC P0751.

Has the test run and passed?

System OK

Go to Step 1