DTC P0751 1-2 Shift Solenoid Valve Performance. Chevrolet PJJ 2000

For 1990-2009 cars
Automatic Transmission Components
Automatic Transmission Controls Schematics
OBD II Symbol Description Notice

### Circuit Description

The 1-2 shift solenoid (1-2 SS) valve is a normally-open exhaust valve that, in conjunction with the 2-3 shift solenoid (2-3 SS) valve, allows 4 different shifting combinations. The 1-2 SS valve is attached to the control valve body, within the transmission.

The PCM monitors the actual gear ratio, and compares the actual gear ratio with the commanded gear ratio. DTC P0751 sets under four conditions:

• | A stuck ON 1-2 SS valve

• | A stuck OFF 1-2 SS valve

• | A stuck ON 1-2 shift valve

• | A stuck OFF 1-2 shift valve

When the PCM detects an actual gear ratio that does not agree with the commanded gear, then DTC P0751 sets. DTC P0751 is a type B DTC.

### Conditions for Running the DTC

• | No TP DTCs P0121, P0122, or P0123.

• | No VSS DTCs P0502 or P0503.

• | No AT ISS DTCs P0716 or P0717.

• | No shift solenoid electrical DTCs P0753 or P0758.

• | No TFP manual valve position switch DTC P1810.

• | The engine is running.

• | The TFP manual valve position switch is not indicating PARK, REVERSE, or NEUTRAL.

• | The transmission fluid temperature is greater than 21°C (70°F).

• | The TP is greater than 8%.

• | The vehicle speed is greater than 8 km/h (5 mph).

• | Engine torque is greater than 14 N·m (10 lb ft).

### Conditions for Setting the DTC

One of the following cases occurs twice during the same trip:

#### Case 1

• | The PCM commands 1st gear and the gear ratio is 1.54:1-1.71:1 (2nd gear) for 2 seconds.

• | The PCM commands 4th gear and the gear ratio is 0.91:1-1.07:1 (3rd gear) for 5 seconds.

#### Case 2

• | The PCM commands 2nd gear and the gear ratio is 2.87:1-3.13:1 (1st gear) for 4 seconds.

• | The PCM commands 3rd gear and the gear ratio is 0.61:1-0.72:1 (4th gear) for 5 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) during the second consecutive trip in which the Conditions for Setting the DTC are met.

• | The PCM commands maximum line pressure.

• | The PCM inhibits TCC engagement.

• | The PCM inhibits 3-2 downshifts above 51 km/h (32 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 during the second consecutive trip in which the Conditions for Setting the DTC are met.

### 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

• | If you clear DTC P0751, and then cannot reset DTC P0751, inspect for the following conditions:

- | Fluid contamination

- | Plugged fluid circuits

- | Restricted fluid circuits

• | Inspect for a stuck TP sensor.

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step verifies that the gear ratio is correct for the commanded gear.

2. This step tests for a mechanical or hydraulic condition causing the 1-2 SS valve to be stuck ON, or the circuit to be applied.

3. This step tests for a mechanical or hydraulic condition causing the 1-2 SS valve to be stuck OFF, or the circuit to be released.

#### DTC P0751 1-2 Shift Solenoid 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
2 | Did you perform the Transmission Fluid Checking Procedure? | -- | Go to Step 3 | Go to Transmission Fluid Check

3

1. Install a Scan Tool .
2. 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.

3. Record the DTC Freeze Frame and Failure Records.
4. Clear the DTC.
5. Use the Scan Tool snapshot mode in order to record current gear and gear ratio.
6. Drive the vehicle in D4, in order to obtain 1-2, 2-3 and 3-4 shifts with a TP greater than 8%.

When the current gear is 2nd, is the gear ratio within the specified range?

2.87:1-3.13:1

Go to Step 5

Go to Step 4

4 | When the current gear is 1st, is the gear ratio within the specified range? | 1.54:1-1.71:1 | Go to Step 6 | Go to Step 5
5 | When the current gear is 3rd, is the gear ratio within the specified range? | 0.61:1-0.72:1 | Go to Step 7 | Go to Step 6
6 | When the current gear is 4th, is the gear ratio within the specified range? | 0.91:1-1.07:1 | Go to Step 8 | Go to Diagnostic Aids

7

1. Inspect the 1-2 shift circuit for the following conditions:

• | 1-2 SS valve mechanically stuck ON.

• | Refer to Shift Solenoid Leak Test .

• | 1-2 shift valve stuck in the applied position.

2. Repair the circuit as necessary.

Refer to Transmission Overhaul in the 4T40-E/4T45-E Section of the Transmission Unit Repair Manual.

Did you complete the repair?

--

Go to Step 9

--

8

1. Inspect the 1-2 shift circuit for the following conditions:

• | 1-2 SS valve mechanically stuck OFF.

• | Refer to Shift Solenoid Leak Test .

• | Damaged 1-2 SS valve O-ring

• | 1-2 shift valve stuck in the released position.

2. Repair the circuit as necessary.

Refer to Transmission Overhaul in the 4T40-E/4T45-E Section of the Transmission Unit Repair Manual.

Did you complete the repair?

--

Go to Step 9

--

9

Perform the following procedure in order to verify the repair:

1. Select DTC.
2. Select Clear Info.
3. Operate the vehicle under the following conditions:

• | Drive the vehicle in D4.

• | Allow the transmission to shift through all the gears.

• | Monitor the current gear and gear ratios. The actual gear ratios must match the commanded gears for 0.75 seconds, for all gears.

4. Select Specific DTC. Enter DTC P0751.

Has the test run and passed?

--

System OK

Go to Step 1