Circuit Description
The 1-2 shift solenoid (SS) valve controls the fluid flow acting on
the 1-2 and 3-4 shift valves. The 1-2 SS valve is a normally-open exhaust
valve that is used with the 2-3 SS valve, in order to allow four different
shifting combinations.
When the PCM 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 TP angle is 10-35%. |
| • | The TP angle is constant +/-5%. |
| • | The transmission fluid temperature is 20-130°C (68-266°F). |
| • | The PCM commands a 1-2, 2-3, and 3-4 shift. |
| • | The TCC is commanded ON. |
| • | The vehicle speed is greater than 8 km/h (5 mph). |
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 50 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 0.95 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 0.65 to 0.8. |
| • | The TCC slip speed is -20 to +40 RPM for 4 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM commands D2 line pressure. |
| • | The PCM inhibits 3-2 downshifts if the vehicle speed is
greater than 48 km/h (30 mph). |
| • | The PCM freezes shift adapts from being updated. |
| • | The PCM records the operating conditions when the Conditions for
Setting the DTC are met. The PCM stores this information as Freeze Frame and
Failure Records. |
| • | The PCM stores DTC P0751 in PCM history. |
Conditions for Clearing the MIL/DTC
| • | 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. |
| • | The PCM clears the DTC from PCM history if the vehicle completes
40 warm-up cycles without an emission-related diagnostic fault
occurring. |
| • | The PCM 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 PCM. |
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 PCM commanded all shifts, that all shift solenoid
valves responded correctly, but that all the shifts did not occur.
DTC P0751 1-2 SS Valve Performance
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 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 1-1-4-4 or 2-2-3-3 shift pattern?
| --
|
Go to Step 3
| Go to
Diagnostic Aids
|
3
| Check 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 under the following conditions (only if
traffic and road conditions permit):
| • | Hold the throttle at 20% and accelerate to 88 km/h (55 mph). |
| • | If the throttle moves more than 5%, stop the vehicle and start
over. |
- Select Specific DTC.
- Enter DTC P0751.
Has the test run and passed?
| --
| System OK
|
Go to Step 1
|
