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 Lo/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 PCM 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.
Conditions for Running the DTC
| • | No VSS DTC P0502 or P0503. |
| • | No AT ISS sensor DTC P0716 or P0717. |
| • | The vehicle speed is greater than 8 km/h (5 mph). |
| • | The TP angle is greater than 5 percent. |
| • | The transmission fluid temperature is greater than 10°C (50°F). |
| • | The engine torque is 27-407 N·m (20-300 lb ft). |
Conditions for Setting the DTC
The PCM commands 2nd gear and the ratio indicates 1st gear, 2.87:1 to 2.97:1 for 2 seconds.
Action Taken When the DTC Sets
| • | The PCM does not illuminate the malfunction indicator lamp (MIL). |
| • | The PCM disables TAP Shift operation. |
| • | The PCM freezes transmission adaptive functions. |
| • | The PCM inhibits 3-2 downshifts when the vehicle speed is greater than 48 km/h (30 mph). |
| • | The PCM records the operating conditions when the Conditions for Setting the DTC are met. The PCM stores this information as Failure Records. |
| • | The PCM stores DTC P1750 in PCM history. |
Conditions for Clearing the DTC
| • | A scan tool can clear the DTC. |
| • | The PCM clears the DTC from PCM history if the vehicle completes 40 warm-up cycles without a non-emission related diagnostic fault occurring. |
| • | The PCM cancels the DTC default actions when the fault no longer exists and the DTC passes. |
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 - Engine Controls? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Controls in Engine Controls - 3.8L | ||||||||
2 | Did you perform the Transmission Fluid Checking Procedure? | -- | Go to Step 3 | Go to Transmission Fluid Check | ||||||||
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 PCM. Is DTC P0753 also set? | -- | Go to DTC P0753 | Go to Step 4 | ||||||||
4 |
Did the gear ratios indicate a 1-1-3-4 shift pattern? | 1st: 2.87:1 to 2.97:1 2nd: 1.52:1 to 1.62:1 3rd: 0.95:1 to 1.05:1 4th: 0.65:1 to 0.75:1 | Go to Step 5 | Go to Diagnostic Aids | ||||||||
5 | Inspect the 1-2 shift valve/hydraulic circuit for the following conditions:
Refer to the following procedures:
Did you find and correct the condition? | -- | Go to Step 6 | -- | ||||||||
6 | Perform the following procedure in order to verify the repair:
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? | -- | Go to Diagnostic Trouble Code (DTC) List in Engine Controls - 3.8L | System OK |
