DTC P0751 1-2 Shift Solenoid Valve Performance Gas LQ4
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 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 TFP manual valve position switch DTC P1810. |
| • | No TCC PWM solenoid valve DTC P1860. |
| • | No TCC Stuck-OFF DTC P0741. |
| • | The system voltage is 8.0-18.0 volts. |
| • | The engine must be running more than 300 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 108 N·m (80 lb ft) to 542 N·m (400 lb ft). |
| • | The commanded gear is not 1st. |
| • | The TFP manual valve position switch indicates D4. |
| • | 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 3.5 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 PCM illuminates the malfunction indicator lamp (MIL) for California emissions vehicles. |
| • | The PCM commands maximum line pressure. |
| • | The PCM inhibits 3-2 downshifts above 25 mph. |
| • | The PCM freezes shift adapts. |
| • | The PCM stores DTC P0751 in PCM history. |
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 consecutive 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 consecutive 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. |
| • | 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.
DTC 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
|
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 PCM.
- 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.
Does each selected transmission range match the scan tool TFP switch display? (Refer to the
Range Signal
table.)
| --
|
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.
Was a 2-2-3-3 or 1-1-4-4 shift pattern only detected? (The vehicle may need to be road tested.)
| --
|
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 circuits for a stuck 1-2 or 3-4 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 corrected?
| --
|
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 PCM 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
|
