DTC P0751 1-2 Shift Solenoid Valve Performance Gas
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 vehicle control module (VCM) detects a 2-2-3-3
gear ratio or a 1-1-4-4 gear ratio, then DTC P0751
sets. DTC P0751 is a type D DTC. For California
emissions vehicles DTC P0751 is a type B DTC.
Conditions for Running the DTC
| • | No MAF sensor DTCs P0101, P0102 or P0103. |
| • | No MAP sensor DTCs P0106, P0107, or P0108. |
| • | No TP sensor DTCs P0121, P0122, or P0123. |
| • | No OSS DTCs P0502 or P0503. |
| • | No ISS sensor DTCs P0716 or P0717. |
| • | No 1-2 SS valve DTC P0753. |
| • | No 2-3 SS valve DTC P0758. |
| • | No TFP manual valve position switch DTC P1810. |
| • | No TCC PWM solenoid valve DTC P1860. |
| • | The engine must be running more than 475 RPM for 7 seconds. |
| • | The vehicle speed is greater than 3 km/h (2.0 mph). |
| • | The TP sensor is greater than 10%. |
| • | The engine torque is 80 N·m (60 lb ft)
to the following: |
| - | 540 N·m (400 lb ft) 5.7L |
| - | 675 N·m (500 lb ft) 7.4L. |
| • | The transmission fluid temperature (TFT) is greater than 20°C
(68°F). |
Conditions for Setting the DTC
All conditions for running the DTC are met, and one of the following
conditions occur:
Stuck Off (after two occurrences)
When the 1-2 SS valve is stuck OFF, first gear is commanded and the
ratio is equal to second gear for greater than 2.0 seconds, and 4th
gear is commanded with the TCC locked and the ratio equals 3rd gear for
greater than 3 seconds.
Stuck On (after five occurrences)
When the 1-2 SS valve is stuck ON, second gear is commanded and the
ratio is equal to first gear for greater than 3 seconds.
Action Taken When the DTC Sets
| • | The VCM illuminates the malfunction indicator lamp (MIL) for California
emissions vehicles. |
| • | The VCM commands maximum line pressure. |
| • | The VCM inhibits 3-2 downshifts above 25 mph. |
| • | The VCM freezes shift adapts. |
| • | The VCM stores DTC P0751 in VCM history. |
Conditions for Clearing the MIL/DTC
| • | For California emissions, the VCM turns OFF the MIL during the
third consecutive trip in which the diagnostic test runs and passes. |
| • | A scan tool clears the DTC from VCM history. |
| • | For California emissions, the VCM clears the DTC from VCM history
if the vehicle completes 40 consecutive warm-up cycles without an emission
related diagnostic fault occurring. |
| • | For Federal emissions, the VCM clears the DTC from VCM history
if the vehicle completes 40 consecutive warm-up cycles without a non-emission
related diagnostic fault occurring. |
| • | The VCM 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
VCM. |
Diagnostic Aids
| • | Verify that the transmission meets the specifications in the
Shift Speed
table. |
| • | Other internal transmission failures can cause more than one shift
to occur. |
| • | First diagnose and clear any engine DTCs or TP sensor codes that
are present. Then inspect for any transmission DTCs that may have reset. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step tests the function of the TFP manual valve position switch.
-
This step tests whether the scan tool commanded all the shifts, or whether
all the shift solenoids responded correctly, but all of the correct shifts
did not occur.
P0751
Step
| Action
| Value(s)
| Yes
| No
|
1
| Was the Powertrain On-Board Diagnostic (OBD) System Check
performed?
| --
|
Go to Step
2
| Go to
Powertrain On Board Diagnostic (OBD) System Check
(5.7L) or
Powertrain On Board Diagnostic (OBD) System Check
(7.4L)
|
2
|
- Install the Scan Tool
.
- With the engine OFF, turn the ignition switch to the RUN position.
Important: Before clearing the DTCs, 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 Freeze Frame and Failure Records.
- Clear the DTCs.
- Select TFP switch A/B/C on the scan tool.
- With the engine operating, apply the brake pedal, and select each
transmission range: D1, D2, D3, D4, N, R, and P.
Refer to the
Range Signal
table.
Does each selected transmission range match the scan tool TFP switch
display?
| --
|
Go to Step
3
| Go to
DTC P1810 TFP Valve Position Switch Circuit
|
3
|
- Raise and support the drive axle assembly.
- Start the engine.
- With the transmission in D4 range, use the scan tool in order
to command first, second, third, and fourth gears while accelerating the
vehicle.
Did you detect a 2-2-3-3 or 1-1-4-4 shift pattern only? (You may need
to road test the vehicle).
| --
|
Go to Step 4
| Go to Diagnostic Aids
|
4
|
- Inspect the shift solenoid/hydraulic circuit for a 1-2 SS valve
internal malfunction.
- Inspect the shift solenoid/hydraulic circuit for a stuck 1-2 shift
valve.
- Inspect the shift solenoid/hydraulic circuit for damaged seals
on one or both of the shift solenoids. The shift solenoids can cause oil
to leak into the second gear clutch pack.
Refer to
Symptom Diagnosis
.
Was the condition found?
| --
|
Go to Step 5
| Go to Diagnostic Aids
|
5
| Perform the following procedure in order to verify the repair:
- Select DTC.
- Select Clear Info.
- Operate the vehicle under the following conditions (If traffic
and road conditions permit):
| • | Accelerate the vehicle with the TP angle greater than 12%
up to 55 mph. |
| • | The VCM must see the proper ratio for each commanded gear for
greater than one second in D1, D2, D3, and D4 (wait for the TCC Lock-up in
4th gear). |
- Select Specific DTC.
- Enter DTC P0751.
Has the test run and passed?
| --
| System OK
|
Go to Step 1
|
