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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC K Pickup - 4WD 🢒 DTC 🢒 DTC P0751 1-2 Shift Solenoid Valve Performance

Object Number: 42270 Size: MF
Automatic Transmission Components
Automatic Transmission Controls Schematics 4L60
OBD II Symbol Description Notice

Circuit Description

The 1-2 Shift Solenoid Valve (1-2 SS Valve) controls the fluid flow acting on the 1-2 and 3-4 shift valves. The solenoid is a normally-open exhaust valve. With the 2-3 Shift Solenoid Valve (2-3 SS Valve), the 1-2 SS Valve allows four different shifting combinations.

When the VCM detects a 1-1-4-4 or a 2-2-3-3 shift pattern, depending on the state of the mechanical failure, then DTC P0751 sets. DTC P0751 is a type A DTC.

Conditions for Setting the DTC
    • No TP Sensor DTCs P0122 or P0123.
    • No VSS Assy. DTCs P0502 or P0503.
    • No TCC Sol. Valve DTC P0740.
    • No TCC Stuck ON DTC P0742.
    • No 1-2 SS Valve DTC P0753.
    • No 2-3 SS Valve DTC P0758.
    • No 3-2 SS Valve Assy. DTC P0785.
    • No TFP Val. Position Sw. DTC P1810.
    • No TCC PWM Sol. Valve DTC P1860.
    • The gear range is D4.
    • The vehicle speed is greater than 8 km/h (5 mph).
    • The engine speed is greater than 450 RPM for 5 seconds.
    • The transmission fluid temperature is 20-130°C (68-266°F).
    • Not in fuel cutoff.

All the above conditions are met three times and the combination of Conditions 1,2,3 and 4 or Conditions 1,2,3 and 5 occurs three times:

Condition 1

    • The VCM commands a 1-2 shift.
    • The TP angle is 10-45%.
    • The TP angle is constant within +/- 7%.
    • The vehicle speed is 8-56 km/h (5-35 mph).
    • Within 2 seconds, the engine speed in 2nd gear is 80 RPM greater than the last speed in 1st gear.

Condition 2

    • The VCM commands a 2-3 shift.
    • The TP angle is 10-45%.
    • The TP angle is constant within +/- 7%.
    • The vehicle speed is 32-80 km/h (20-50 mph).
    • Within 2 seconds, the engine speed in 3rd gear is 100 RPM less than the last speed in 2nd gear.

Condition 3

    • The VCM commands a 3-4 shift.
    • The TP angle is 10-45%.
    • The TP angle is constant within +/- 7%.
    • The vehicle speed is 48-105 km/h (30-65 mph).
    • Within 2 seconds, the engine speed in 4th gear is 10 RPM greater than the last speed in 3rd gear.

Condition 4

    • The VCM commands 4th gear.
    • The TCC is ON.
    • The TP angle is 8-35%.
    • The speed ratio is 0.85 to 1.2 (speed ratio is engine speed divided by output speed).
    • The TCC slip speed is 200-1000 RPM for 4 seconds.

Condition 5

    • The VCM commands 4th gear.
    • The TCC is ON.
    • The TP is 8-35%.
    • The speed ratio is 0.6 to 0.8.
    • The TCC slip speed is -20 to +50 RPM for 4 seconds.

Action Taken When the DTC Sets
    • The VCM illuminates the Malfunction Indicator Lamp (MIL).
    • The VCM commands D2 line pressure.
    • The VCM freezes shift adapts from being updated.
    • DTC P0751 stores in VCM history.

Conditions for Clearing the MIL/DTC
    • The VCM turns OFF the MIL after three consecutive trips 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 4L60-E Shift Speed table.
    • Other internal transmission failures may cause more than one shift to occur.
    • Refer to the Shift Solenoid Valve State and Gear Ratio table.

Test Description

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

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

DTC P0751 1-2 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 (4.3L) or Powertrain On Board Diagnostic (OBD) System Check (5.0L, 5.7L) in Engine Controls

2

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

    3. Important: Before clearing the DTC(s), 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 VCM.

  3. Record the DTC Freeze Frame and Failure Records, then clear the DTC(s).
  4. Drive the vehicle in D4 range, under the following conditions:

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

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

--

Go to Step 3

Go to Diagnostic Aids

3

Check the shift solenoid/hydraulic circuit for the following conditions:

    • An internal malfunction.
    • Damaged seals on one or both of the shift solenoid valves.

Did you find and correct the condition?

--

Go to Step 4

--

4

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

  1. Select DTC.
  2. Select Clear Info.
  3. Drive the vehicle in D4 range under the following conditions (only if traffic and road conditions permit):

    4. Hold the throttle at 20% and accelerate to 55 mph. If the throttle moves more than 7%, stop the vehicle and start over.

  4. Select Specific DTC.
  5. Enter DTC P0751.

Has the test run and passed?

--

System OK

Begin the diagnosis again. Go to Step 1