Circuit Description
The 1-2 shift solenoid (SS) valve controls the fluid flow action
on the 1-2 and the 3-4 shift valves. The 1-2 SS valve is
a normally open exhaust valve that is used with the 2-3 SS in order to
allow four different shifting combinations.
When the powertrain control module (PCM) detects a 2-2-3-3
gear ratio, then DTC P0751 sets. DTC P0751 is a type C DTC.
For California emissions vehicles 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 sensor DTC P0101, P0102 or P0103. |
| • | No MAP sensor DTCs P0106, P0107, or P0108. |
| • | No TP sensor DTCs P0121, P0122 or P0123. |
| • | No VSS DTCs P0502 or P0503. |
| • | No AT ISS sensor DTCs P0716 or P0717. |
| • | No TCC Stuck ON DTC P0742. |
| • | No shift solenoid electrical DTC P0753 or P0758. |
| • | No Transmission Component Slipping DTC P0894. |
| • | No TFP manual valve position switch DTC P1810. |
| • | No TCC PWM solenoid valve DTC P2761. |
| • | The system voltage is 10-18 volts. |
| • | The AT OSS is greater than 7 RPM. |
| • | AT ISS is greater than 7 RPM. |
| • | The TP sensor is 10-100 percent. |
| • | The engine torque must be between 108 N·m (80 lb ft)
and: |
| - | 4.8L: 542 N·m (400 lb ft) |
| - | 6.0L: 576 N·m (425 lb ft) |
| • | No TFP manual valve position switch change within 6 seconds. |
| • | The TFP manual valve position switch indicates D4. |
| • | The transmission fluid temperature (TFT) is greater than 20°C
(68°F) and less than 130°C (266°F). |
Conditions for Setting the DTC
| • | The commanded gear equals 1st and the ratio equals 2nd for greater than
2 seconds. |
| • | The commanded gear equals 4th with the TCC locked and the ratio equals
3rd for greater than 3.75 seconds. |
| • | All conditions are met for 2 occurrences. |
Action Taken When the DTC Sets
| • | For California emission equipped vehicles, the PCM illuminates the malfunction
indicator lamp (MIL) during the second consecutive trip in which the Conditions for
Setting the DTC are met. For Federal emission equipped vehicles, the MIL is not illuminated. |
| • | The PCM commands maximum line pressure. |
| • | The PCM freezes transmission adaptive functions. |
| • | The PCM records the operating conditions when the Conditions for Setting
the DTC are met. The PCM stores this information as Freeze Frame, California only,
and Failure Records, California and Federal. |
| • | The PCM stores the DTC P0751 in PCM history during the second consecutive
trip, California, or the first trip, Federal, in which the Conditions for Setting
the DTC are met. |
Conditions for Clearing the MIL/DTC
| • | For California emissions, the PCM 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. |
| • | For California emissions, the PCM clears the DTC from PCM history
if the vehicle completes 40 warm-up cycles without an emission
related diagnostic fault occurring. |
| • | For Federal emissions, 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 ignition switch is OFF long enough in order to power down
the PCM. |
Diagnostic Aids
| • | Verify that the transmission meets the specifications in the Shift Speed
table. Refer to
Shift Speed
. |
| • | Other internal transmission failures can cause more than one shift to
occur. |
| • | DTC P0751 defaults to an elevated line pressure condition which may result
in partial TCC apply. This may produce an idle surge that could stall the engine. |
Test Description
The number below refers to the step number on the diagnostic table.
-
This step tests that the PCM commanded all shifts,
that all shift solenoid valves responded correctly, but that all the shifts did not
occur.
Step
| Action
| Yes
| No
|
1
| Did you perform the Diagnostic System Check - Vehicle?
| Go to
Step 2
| Go to
Diagnostic System Check - Vehicle
in Vehicle DTC Information
|
2
|
- Install a scan tool.
- Turn ON the ignition, with the engine OFF.
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 PCM.
- Record the DTC Freeze Frame and Failure Records.
- Clear the DTC.
- Drive the vehicle in D4 range under the following conditions:
Accelerate the vehicle, ensuring that the PCM commands 1st, 2nd, 3rd and 4th gears.
Did you detect a 2-2-3-3 shift pattern?
| Go to
Step 3
| Go to
Intermittent Conditions
in Engine
Controls - 4.8L, 5.3L, and 6.0L
|
3
|
- Inspect the shift solenoid/hydraulic circuit for the following conditions:
| • | 1-2 shift valve stuck in the released position |
- Clean and inspect the related valves, bores and the valve body for debris
or contamination restricting valve movement. Refer to
Control Valve Body Cleaning and Inspection
in Transmission Unit Repair
Manual.
Did you find and correct the condition?
| Go to
Step 4
| --
|
4
| Perform the following procedure in order to verify the repair:
- Select DTC.
- Select Clear Info.
- Drive the vehicle in D4 range under the following condition, only if traffic
and road conditions permit:
Hold the throttle at 40% and accelerate to
89 km/h (55 mph).
- Select Specific DTC.
- Enter DTC P0751.
Has the test run and passed?
| Go to
Step 5
| Go to
Step 2
|
5
| 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?
| Go to
Diagnostic Trouble Code (DTC) List - Vehicle
in Vehicle DTC Information
| System OK
|
