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 (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. |
| • | No OSS DTCs P0722 or P0723. |
| • | The engine is running for 5 seconds. |
| • | The vehicle speed is greater than 24 km/h (15 mph). |
| • | The calc. throttle position is greater than 8 percent. |
| • | The transmission fluid temperature is 20°C (68°F) or more. |
| • | The engine torque is greater than 50 N·m (37 lb ft). |
| • | The time since the last gear change is 2 seconds. |
Conditions for Setting the DTC
The TCM commands 2nd gear and the gear ratio is 2.81:1-3.10:1 for 3.25 seconds.
Action Taken When the DTC Sets
| • | The TCM does not request the ECM to 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 freezes transmission adaptive functions. |
| • | The TCM disables TAP shift operation, if equipped. |
| • | The TCM commands an alternate coast shift pattern where downshifts occur at higher vehicle speeds while coasting. |
| • | 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 fault no longer exists an d 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 - Vehicle? | -- | Go to Step 2 | |||||||||
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 TCM. Is DTC P0752 also set? | -- | Go to DTC P0752 | Go to Step 4 | ||||||||
4 |
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: 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: 1.54:1 to 1.71:1 | 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? | -- | System OK |
