Circuit Description
The 1-2 shift solenoid (SS) valve is a normally-open exhaust valve that, in conjunction with the 2-3 shift solenoid (SS) valve, allows four different shifting combinations. The 1-2 SS valve is attached to the control valve body, within the transmission.
The transmission control module (TCM) monitors the actual gear ratio, and compares the actual gear ratio with the commanded gear ratio. DTC P0751 sets under two conditions:
| • | A stuck OFF 1-2 SS valve |
| • | A stuck OFF 1-2 shift valve |
When the TCM detects a 2-2-3-3 shift pattern, then DTC P0751 sets. DTC P0751 is a type B DTC.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0751 1-2 Shift Solenoid Valve Performance - No First or Fourth Gear
Conditions for Running the DTC
| • | No MAP DTCs P0107 or P0108. |
| • | No TP DTCs P0120 or P0220. |
| • | No ISS DTCs P0716 or P0717. |
| • | No OSS DTCs P0722 or P0723. |
| • | No TCC stuck ON DTC P0742. |
| • | No 1-2 SS electrical DTCs P0973 or P0974. |
| • | No 2-3 SS electrical DTCs P0976 or P0977. |
| • | The engine is running for 5 seconds. |
| • | The transmission fluid temperature (TFT) is 20°C to 130°C (68°F to 266°F). |
| • | The calc. throttle position is 8 percent or more. |
| • | The input speed is 150-6,000 RPM. |
| • | The output speed is 200 RPM or more. |
| • | The engine torque is greater than 50 N·m (37 lb ft). |
| • | The time since the last gear change is 1.0 second. |
Conditions for Setting the DTC
The following occurs twice during the same trip:
| • | The TCM commands 1st gear and the gear ratio is 1.54:1-1.71:1, 2nd gear, for 2 seconds. |
| • | The TCM commands 4th gear and the gear ratio is 0.95:1-1.05:1, 3rd gear, for 4 seconds. |
Action Taken When the DTC Sets
| • | The TCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met. |
| • | The TCM commands maximum line pressure. |
| • | 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 Freeze Frame and Failure Records. |
| • | The TCM stores DTC P0751 in TCM history during the second consecutive trip in which the Conditions for Setting the DTC are met. |
Conditions for Clearing the MIL/DTC
| • | The TCM turns OFF the MIL during the third consecutive trip in which the diagnostic test runs and passes. |
| • | A scan tool can clear the MIL/DTC. |
| • | The TCM clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without an 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 you clear DTC P0751, and then cannot set DTC P0751 again, inspect for the following conditions: |
| - | Fluid contamination |
| - | Plugged fluid circuits |
| - | Restricted fluid circuits |
| • | Refer to Shift Solenoid Valve State and Gear Ratio . |
| • | It is possible for an internal TCM failure which may not allow sufficient current to operate the solenoids. Verify TCM functionality by commanding the suspected solenoid ON/OFF using the scan tool and listen for a click. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies a 2-2-3-3 shift pattern.
-
This step tests for a mechanical or hydraulic condition causing the 1-2 SS valve to be stuck OFF, or the circuit to be released.
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 | ||||||||
Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records. Using the Clear Info function erases the Freeze Frame and Failure Records from the TCM. Are the current gear and gear ratio within the specified values? | 1st/2nd: 1.54:1-1.71:1 3rd/4th: 0.95:1-1.05:1 | Go to Step 4 | Go to Diagnostic Aids | |||||||||
Refer to 1-2 Shift Solenoid Valve Replacement . Did you complete the repair? | -- | Go to Step 5 | -- | |||||||||
5 | Perform the following procedure in order to verify the repair:
Has the test run and passed? | -- | Go to Step 6 | Go to Step 2 | ||||||||
6 | With the 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 |
