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

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1996 🢒 GMC Suburban - 2WD 🢒 DTC 🢒 DTC P0751 1-2 Shift Solenoid Valve Performance

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

Table 1:	Shift Solenoid State and Gear Ratio Table
Table 2:	DTC P0751 1-2 Shift Solenoid Valve Performance (5.7L and 7.4L Gas)

Automatic Transmission Components 5.7L and 7.4L Gas
Automatic Transmission Controls Schematics 5.7L and 7.4L
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 VCM detects an incorrect Gear Ratio, then DTC P0751 sets. DTC P0751 is a type A DTC.

Conditions for Setting the DTC

•	No MAP Sensor DTCs P0106, P0107 or P0108.

•	No TP Sensor DTCs P0121, P0122 or P0123.

•	No VSS DTC P0502.

•	No 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 for 5 seconds and not in fuel cutoff.

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

•	The TP Sensor is greater than 12%.

•	The Engine Torque is 70 lb ft (88 N·m) to the following:

-	275 lb ft (345 N·m) 4.3L

-	375 lb ft (470 N·m) 5.7L

-	500 lb ft (627 N·m) 7.4L.

•	The transmission fluid temperature is greater than 20°C (68°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:

-	When the 1-2 SS Valve is stuck OFF, first gear is commanded and the ratio is equal to second gear for greater than 2.0 seconds. (2.5 seconds for 4.3L) and 4th gear is commanded with the TCC locked and the ratio equals 3rd for greater than 3 seconds.

-	When the 1-2 SS Valve is stuck ON, second gear is commanded and the ratio is equal to first gear for greater than 3 seconds.

Action Taken When the DTC Sets

•	The VCM commands maximum line pressure.

•	The VCM freezes shift adapts.

•	The VCM illuminates the Malfunction Indicator Lamp (MIL) for California emissions vehicles.

Conditions for Clearing the DTC

•	For California emissions only, the VCM turns OFF the MIL after three consecutive ignition cycles without a failure reported.

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

•	The VCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the VCM.

Diagnostic Aids

•	Verify that the transmission meets the specifications in the 4L80-E shift speed table.

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

•	First diagnose and clear any engine DTCs or TP Sensor codes that are present. Then inspect for any transmission DTCs that may have reset.

Shift Solenoid State and Gear Ratio Table

Gear	1-2 SS Valve	2-3 SS Valve	Gear Ratio
1	ON	OFF	2.48:1
2	OFF	OFF	1.48:1
3	OFF	ON	1.00:1
4	ON	ON	0.75:1

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.

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

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 (tech 1) ®.
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.
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 Trans Range on the scan tool?

Go to Step 3

Go to DTC P1810 Pressure Switch Assembly Malfunction

With the engine running, raise the drive wheels.
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 for a stuck 1-2 shift valve.
Inspect the shift solenoid/hydraulic circuit for damaged seals on one or both of the shift solenoids. The shift solenoids can leak oil into the second gear clutch pack.
Refer to the diagnosis tables.

Did you find and correct a condition?

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 at 20% and accelerate to 55 mph.

•	The VCM must see the proper ratio for each commanded gear for greater than one second in D1, D2, D3, and D4 (wait for the TCC Lock-up in 4th gear).

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 6.5L Diesel

Table 1:	Shift Solenoid State and Gear Ratio Table
Table 2:	DTC P0751 1-2 Shift Solenoid Valve Performance (6.5L Diesel)

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