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 4 different shifting combinations. The 1-2 SS valve is attached to the lower 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 |
If 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 MAF DTCs P0101, P0102 or P0103. |
| • | No MAP DTCs P0106, P0107 or P0108. |
| • | No OSS DTCs P0722 or P0723. |
| • | No AT ISS DTCs P0716 or P0717. |
| • | No shift solenoid electrical DTCs P0973, P0974, P0976 or P0977. |
| • | No TCC stuck ON DTC P0742. |
| • | The engine run time is greater than 5 seconds. |
| • | The time since the gear select lever change is 1 second. |
| • | The transmission fluid temperature is 20-130°C (68-266°F). |
| • | The TP angle is 8 percent or greater. |
| • | LD8: The transmission output shaft speed is 200 RPM or greater. |
| • | L37: The transmission output shaft speed is 239 RPM or greater. |
| • | The engine torque is 50-1492 N·m (37-1100 lb ft). |
Conditions for Setting the DTC
The following conditions occur twice during the same trip:
| • | The TCM commands 1st gear and the gear ratio is 1.54:1-1.71:1 for 2 seconds. |
| • | The TCM commands 4th gear and the gear ratio is 0.95:1-1.05:1 for 4 seconds. |
Action Taken When the DTC Sets
| • | The TCM requests the engine control module (ECM) to illuminate 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 ECM records the operating conditions when the Conditions for Setting the DTC are met. The ECM stores this information as Freeze Frame and Failure Records and 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 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 ECM turns OFF the MIL after the third consecutive drive trip in which the TCM does not send a MIL illumination request. |
| • | The TCM clears the DIC message when the condition no longer exists. |
| • | 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 reset DTC P0751, the following conditions may exist: |
| - | Fluid contamination |
| - | Plugged fluid circuits |
| - | Restricted fluid circuits |
| - | Sticking 1-2 SS |
| - | Sticking 1-2 shift valve |
| • | Refer to Shift Solenoid Valve State and Gear Ratio . |
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 | Values | 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 commanded gear and gear ratio within the specified parameters? | 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 Control Valve Lower Body Disassemble in the 4T80-E section of the Transmission Unit Repair Manual. 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? | 1st 2.75:1-3.17:1 2nd 1.51:1-1.74:1 3rd 0.93:1-1.07:1 4th 0.63:1-0.73:1 | 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 |
