Circuit Description
The 1-2 shift solenoid (SS) valve controls the fluid flow acting on
the 1-2 and 3-4 shift valves. The solenoid is a normally-open exhaust valve.
With the 2-3 SS valve, the 1-2 SS valve allows four different shifting
combinations.
When the VCM detects a 1-1-4-4 or a 2-2-3-3 shift pattern, depending
on the state of the mechanical failure, then DTC P0751 sets. DTC P0751
is a type A DTC.
Conditions for Running the DTC
| • | No TP sensor DTCs P0122 or P0123. |
| • | No VSS assembly DTCs P0502 or P0503. |
| • | No TCC solenoid valve DTC P0740. |
| • | No TCC stuck ON DTC P0742. |
| • | No 1-2 SS valve DTC P0753. |
| • | No 2-3 SS valve DTC P0758. |
| • | No 3-2 SS valve assembly DTC P0785. |
| • | No TFP manual valve position switch DTC P1810. |
| • | No TCC PWM solenoid valve DTC P1860. |
| • | The engine speed is greater than 450 RPM for 5 seconds. |
| • | The engine is not in fuel cutoff. |
| • | The vehicle speed is greater than 8 km/h (5 mph). |
| • | The TP angle is 10-35%. |
| • | The TP angle is constant within +/- 7%. |
| • | The transmission fluid temperature is 20-130°C (68-266°F). |
| • | The VCM commands a 1-2, 2-3 and 3-4 shift. |
| • | The TCC is commanded ON. |
Conditions for Setting the DTC
DTC P0751 sets if the following conditions occur three times:
| • | Within 2 seconds, the engine speed in 2nd gear is 80 RPM
greater than the last speed in 1st gear. |
| • | Within 2 seconds, the engine speed in 3rd gear is 100 RPM
less than the last speed in 2nd gear. |
| • | Within 2 seconds, the engine speed in 4th gear is 10 RPM
greater than the last speed in 3rd gear. |
All of the above conditions are met and one of the following conditions
occurs:
Condition 1
| • | The speed ratio is 0.85 to 1.2 (speed ratio is engine speed divided
by transmission output speed). |
| • | The TCC slip speed is 200-1000 RPM for 4 seconds. |
Condition 2
| • | The speed ratio is 0.6 to 0.8. |
| • | The TCC slip speed is -20 to +50 RPM for 4 seconds. |
Action Taken When the DTC Sets
| • | The VCM illuminates the malfunction indicator lamp (MIL). |
| • | The VCM commands D2 line pressure. |
| • | The VCM freezes shift adapts from being updated. |
| • | The VCM records the operating conditions when the Conditions for
Setting the DTC are met. The VCM stores this information as Freeze Frame and
Failure Records. |
| • | The VCM stores DTC P0751 in VCM history. |
Conditions for Clearing the MIL/DTC
| • | The VCM 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 VCM clears the DTC from VCM history if the vehicle completes
40 warm-up cycles without an emission-related diagnostic fault occurring. |
| • | The VCM cancels the DTC default actions when the fault no longer
exists and/or the ignition switch is OFF long enough in order
to power down the VCM. |
Diagnostic Aids
| • | Verify that the transmission meets the specifications in the
Shift Speed
table. |
| • | Other internal transmission failures may cause more than one shift
to occur. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests that the VCM commanded all shifts, that all shift solenoid
valves responded correctly, but that all the shifts did not occur.
DTC P0751 1-2 Shift Solenoid Valve -- Performance (4.3L)
Step
| Action
| Value(s)
| Yes
| No
|
1
| Did you perform the Powertrain
Diagnostic System Check?
| --
|
Go to Step 2
| Go to
Powertrain On Board Diagnostic (OBD) System Check
in Engine Controls
|
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 VCM.
- 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 VCM commands 1st, 2nd, 3rd,
and 4th gears.
Did you detect a 1-1-4-4 or 2-2-3-3 shift pattern?
| --
|
Go to Step 3
| Go to Diagnostic Aids
|
3
| Inspect the shift solenoid/hydraulic circuit for the following
conditions:
| • | An internal malfunction. |
| • | Damaged seals on the shift solenoid valve. |
| | Refer to Shift Solenoid Leak Test
. |
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 conditions (only
if traffic and road conditions permit):
Hold the throttle at 20% and accelerate to 55 mph. If the throttle
moves more than 7%, stop the vehicle and start over.
- Select Specific DTC.
- Enter DTC P0751.
Has the test run and passed?
| --
| System OK
|
Go to Step
1
|
