DTC P0751 1-2 Shift Solenoid Valve Performance. GMC Truck GMC Suburban

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1997 🢒 GMC Suburban - 4WD 🢒 Transmission/Transaxle 🢒 Automatic Transmission - 4L80-E 🢒 DTC P0751 1-2 Shift Solenoid Valve Performance

DTC P0751 1-2 Shift Solenoid Valve Performance 6.5L Diesel

Automatic Transmission Components Diesel
Automatic Transmission Controls Schematics 6.5 L Diesel Schematics
OBD II Symbol Description Notice

Circuit Description

The 1-2 Shift Solenoid Valve (1-2 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 Shift Solenoid Valve (2-3 SS Valve) to allow four different shifting combinations.

When the Powertrain Control Module (PCM) detects an incorrect Gear Ratio, then DTC P0751 sets. DTC P0751 is a type B DTC.

Conditions for Setting the DTC

•	No MAP Sensor DTCs P0106, P0107, or P0108

•	No OSS DTCs P0722 or P0723

•	No A/T ISS Sensor DTCs P0716 or P0717

•	No 1-2 SS Valve DTC P0753

•	No 2-3 SS Valve DTC P0758

•	No TFP Val. Position Sw. DTC P1810

•	No Four Wheel Drive DTC P1875

•	The engine must be running greater than 475 RPM for at least 7 seconds.

•	The vehicle speed is greater than 4.2 km/h (2.5 mph).

•	The APP Angle is greater than 12%.

•	The Engine Torque is 75-565 N·m (60-450 lb ft).

•	No engine torque malfunctions.

•	The transmission fluid temperature is greater than 20°C (68°F) and less than 130°C (255°F).

•	The engine speed is less than 3650 RPM.

•	Do not put in to Four Wheel Drive Low.

•	All the above conditions are met and one of the following conditions are met:

Stuck Off (after two occurrences)

•	First gear is commanded and the ratio is equal to second gear for greater than 1.5 seconds.

•	Fourth gear is commanded (with TCC locked) and the ratio equals third gear for greater than 3 seconds.

Stuck On (after five occurrences)

•	Second gear is commanded.

•	The ratio equals first gear for greater than 2.5 seconds.

Action Taken When the DTC Sets

•	The PCM commands maximum line pressure.

•	The PCM freezes shift adapts.

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

Conditions for Clearing the DTC

The PCM turns OFF the MIL after three consecutive ignition cycles 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

•	Verify that the transmission meets the specifications in the Shift Speed table.

•	Other internal transmission failures can cause more than one shift to occur.

•	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.

Test Description

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

This step tests the function of the TFP Val. Position Sw.

This step tests whether the scan tool commanded all the shifts, or whether all the shift solenoids responded correctly but all the shifts did not occur.

P0751

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

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.
Select TFP Sw. A/B/C on the scan tool.
With the engine operating, apply the brake pedal, and select each transmission range: D1, D2, D3, D4, N, R, and P.

Does each selected transmission range match the scan tool TFP Switch A/B/C display? (Refer to the Range Signal table.)

Go to Step 3

Go to DTC P1810 Pressure Switch Assembly Malfunction

Raise and support the drive wheels.
Start the engine.
With the transmission in D4 range, use the scan tool in order to command first, second, third, and fourth gears while accelerating the vehicle.

Did you detect a 2-2-3-3 or 1-1-4-4 shift pattern only? (You may need to road test the vehicle).

Go to Step 4

Go to Diagnostic Aids

Inspect the shift solenoid/hydraulic circuit for a 1-2 SS valve internal malfunction.
Inspect the shift solenoid/hydraulic circuit for damaged seals on one or both of the shift solenoids.
Refer to the diagnosis tables.

Did you find and correct a problem?

Go to Step 5

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

Select DTC.
Select Clear Info.
Operate the vehicle under the following conditions (If traffic and road conditions permit):

•	Hold the throttle greater than 12%, and accelerate to 55 mph. If the throttle moves more than 3%, stop the vehicle and start over.

•	The PCM must see the proper ratio for each commanded gear for greater than one second in D1, D2, D3, and D4.

Select Specific DTC. Enter DTC P0751.

Has the test run and passed?

System OK

Begin the diagnosis again. Go to Step 1

DTC P0751 1-2 Shift Solenoid Valve Performance 5.7L and 7.4L Gas

Automatic Transmission Components Gas
Automatic Transmission Controls Schematics 5.7 and 7.4 L Gas Schematics
OBD II Symbol Description Notice