GM Service Manual Online
For 1990-2009 cars only

Object Number: 40580  Size: MF
Master Electrical Component List
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

Circuit Description

The 1-2 shift valve is used to direct fluid for shifting between 1st and 2nd gears. In 1st gear, the 1-2 shift solenoid (1-2 SS) valve is commanded ON causing 1-2, 3-4 signal fluid pressure to overcome the 1-2 shift valve spring force, moving the 1-2 shift valve into a position that routes D4 fluid into the Low/1st fluid passage. In 2nd gear, the 1-2 SS valve is commanded OFF allowing 1-2, 3-4 signal fluid to be exhausted and the 1-2 shift valve spring force then moves the 1-2 shift valve into a position that routes D4 fluid into the 2nd fluid passage.

If the transmission control module (TCM) detects a 1st gear ratio when 2nd gear is commanded indicating a stuck 1-2 shift valve, then DTC P1750 sets. DTC P1750 is a type C DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1750 1-2 Shift Valve Performance

Conditions for Running the DTC

    • No ISS DTCs P0716 or P0717.
    • The engine is running for 5 seconds or more.
    • The vehicle speed is greater than 24 km/h (15 mph).
    • The calc. throttle position is 8 percent or more.
    • The transmission fluid temperature is 20°C (68°F) or more.
    • The engine torque is greater than 50 N·m (37 lb ft).

Conditions for Setting the DTC

The TCM commands 2nd gear for 2 seconds or more and gear ratio is 2.87:1 to 2.97:1 for 3.25 seconds.

Action Taken When the DTC Sets

    • The TCM does not illuminate the malfunction indicator lamp (MIL).
    • The TCM commands maximum line pressure.
    • The TCM inhibits 3-2 downshifts when the vehicle speed is greater than 52 km/h (32 mph).
    • The TCM commands a D4 shift pattern.
    • The TCM commands an alternate coast shift pattern where downshifts occur at higher vehicle speeds while coasting.
    • The TCM freezes transmission adaptive functions.
    • The TCM disables TAP Shift operation.
    • The TCM records the operating conditions when the Conditions for Setting the DTC are met. The TCM stores this information as Failure Records.
    • The TCM stores DTC P1750 in TCM history.

Conditions for Clearing the DTC

    • A scan tool can clear the DTC.
    • The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring.
    • The TCM cancels the DTC default actions when the ignition switch is OFF long enough in order to power down the TCM.

Diagnostic Aids

If DTC P1750 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

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

Did you perform the Transmission Fluid Checking Procedure?

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Go to Step 3

Go to Transmission Fluid Check

3

  1. Install a scan tool.
  2. Turn OFF the ignition, with the engine OFF.
  3. Important: Before clearing the DTCs, use the scan tool in order to record the Failure Records for reference. Using the Clear DTC Information function will erase the Failure Records from the TCM.

  4. Record the Freeze Frame and Failure Records.
  5. Clear the DTCs.

Is DTC  P0752 also set?

--

Go to DTC P0752

Go to Step 4

4

  1. Accelerate the vehicle in D4 range, ensuring that the TCM commands 1st, 2nd, 3rd and 4th gears.
  2. With the scan tool, observe Commanded Gear and Gear Ratio for each gear.

Did the gear ratios indicate a 1-1-3-4 shift pattern?

1st: 2.87:1 to 3.13:1

2nd: 1.54:1 to 1.71:1

3rd: 0.91:1 to 1.07:1

4th: 0.61:1 to 0.71:1

Go to Step 5

Go to Diagnostic Aids

5

Inspect the 1-2 shift valve/hydraulic circuit for a stuck or binding 1-2 shift valve.

Refer to the following procedures:

    •  Control Valve Body Disassemble in Unit Repair

Did you find and correct the condition?

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Go to Step 6

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6

Perform the following procedure in order to verify the repair:

  1. Select DTC.
  2. Select Clear Information.
  3. Operate the vehicle under the following conditions:
  4. • Drive the vehicle in D4.
    • Calc. throttle position must be 8 percent or greater.
    • The engine torque is greater than 50 N·m (37 lb ft).
    • Ensure that the gear ratio is correct for 2nd gear for 1 second.
  5. Select Specific DTC.
  6. Enter DTC P1750.

Has the test run and passed?

2nd: 1.52:1 to 1.62:1

Go to Step 7

Go to Step 2

7

With a scan tool, observe the stored information, capture info and DTC info.

Does the scan tool display any DTCs that you have not diagnosed?

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Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK