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

### Circuit Description

The 1-2 Shift Solenoid is fed ignition voltage by circuit 1339 and the ground path is provided by the Powertrain Control Module (PCM), depending on the solenoids commanded state. When the PCM commands the solenoid OFF, a ground path is not provided and the filtered line pressure to the solenoid is exhausted. When the PCM commands the solenoid ON, a ground path is provided, energizing the solenoid which blocks the exhaust port. This allows line pressure to the fluid passage.

The PCM monitors the commanded gear and the speed ratio in order to identify a malfunction in the 1-2 Shift Solenoid Valve.

When the PCM detects a 2-2-3-3 or a 1-1-4-4 only shift pattern, then DTC P0751 sets. DTC P0751 is a type A DTC.

### Conditions for Setting the DTC

• | No TP DTCs P0122 or P0123.

• | No VSS DTCs P0502 or P0503.

• | No TCC enable solenoid electrical DTC P0740.

• | No TCC stuck ON DTC P0742.

• | No 1-2 solenoid electrical DTC P0753.

• | No 2-3 solenoid electrical DTC P0758.

• | No TCC PWM solenoid electrical DTC P1860.

• | The engine speed is greater than 500 RPM for 5 seconds.

• | Not in fuel shut off.

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

• | The transmission temperature is 20-130°C (68-266°F).

• | The transmission range switch indicates D4.

• | The traction control is not active.

• | All of the above must occur and either fail cases 1, 2, 3 and 4 or 1, 2, 3 and 5 are true 3 times.

Failure Criteria

#### Case 1

• | 1-2 shift is commanded.

• | The throttle position is 18-70% and is constant within 3%.

• | The vehicle speed is 8-64 km/h (5-40 mph).

• | 2nd gear is commanded and, within 2.0 seconds, the engine speed is 110 RPM greater than the last engine speed of the commanded 1st gear.

#### Case 2

• | 2-3 shift is commanded.

• | The throttle position is 10-55% and is constant within 10%.

• | The vehicle speed is 40-89 km/h (25-55 mph).

• | 3rd gear is commanded and, within 2.5 seconds, the engine speed is 130 RPM less than the last engine speed of the commanded 2nd gear.

#### Case 3

• | 3-4 shift is commanded.

• | The throttle position is 5-40% and is constant within 7%.

• | The vehicle speed is 56-121 km/h (35-75 mph).

• | 4th gear is commanded and, within 1.0 second, the engine speed is 1 RPM greater than the last engine speed of the commanded 3rd gear.

#### Case 4

• | Fourth gear is commanded and the TCC is ON.

• | The throttle position is 2-40%.

• | The speed ratio is 0.97-1.18.

• | The TCC slip is 500-1,000 RPM for more than 3 seconds.

#### Case 5

• | Fourth gear is commanded and the TCC is ON.

• | The throttle position is 2-40%.

• | The speed ratio is 0.68-0.82.

• | The TCC slip is 0 to 50 RPM for more than 3.0 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the Malfunction Indicator Lamp (MIL).

• | The PCM inhibits downshifts to 2nd gear if the vehicle speed is greater than 48 km/h (30 mph).

### Conditions for Clearing the MIL/DTC

• | The PCM turns OFF the MIL after three consecutive trips without a failure reported.

• | A scan tool can clear the DTC from the PCM history. The PCM clears the DTC from the PCM history if the vehicle completes 40 warm-up cycles without a failure reported.

• | The PCM cancels the DTC default actions when the fault no longer exists and the ignition is OFF long enough in order to power down the PCM.

### Diagnostic Aids

• | Check for PRNDL DTC P0705. A PRNDL DTC affects transmission operation. A PRNDL DTC may set DTC P0751 falsely.

• | Inspect the transmission fluid for sediment.

• | Inspect the transmission filter for debris.

• | Ensure that the scan tool commanded gear has correct solenoid states and ratio. Refer to Shift Solenoid Valve State and Gear Ratio table.

### Test Description

The number below refers to the step numbers on the diagnostic table.

1. Once the DTC is verified, replace the 1-2 shift solenoid.

#### DTC P0751 1-2 Shift Solenoid Performance

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 in Engine Controls
2 | Did you perform the Transmission Fluid Checking Procedure? | -- | Go to Step 3 | Go to Transmission Fluid Check
3 |

1. Install the Scan Tool .
2. 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 for reference. Using the Clear Info function will erase the stored Freeze Frame and Failure Records from the PCM.

3. Record the DTC Freeze Frame and Failure Records, then clear the DTC.
4. Inspect for the following conditions:

• | Shift solenoid screen assy. for sediment or debris.

• | 1-2 shift solenoid for a damaged or missing O-ring.

• | 1-2 shift valve for sediment or debris and the possibility of a bent or stuck valve.

Refer to Transmission Overhaul in the 4T60-E Section of the Transmission Unit Repair Manual.

Was a condition found and corrected?

--

Go to Step 5

Go to Step 4

4 | Replace the 1-2 Shift Solenoid Valve. Refer to Solenoids and Wiring Harness Replacement . Is the replacement complete? | -- | Go to Step 5 | --
5 | In order to verify your repair, perform the following procedure:

1. Using the Scan Tool , clear DTC information.
2. Operate the vehicle under the following conditions:

• | The traction control is not active.

• | The transmission fluid temperature is 20-130°C (68-266°F)

• | The engine speed is more than 500 RPM for 5 seconds.

• | The vehicle is not in fuel shut off.

• | The gear range is D4.

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

• | All the conditions in the following cases must be met:

#### Case 1

- | The PCM commands a 1-2 shift.

- | The throttle position is 18-70% and constant by 3%.

- | The vehicle speed is 8-64 km/h (5-40 mph).

- | Within 2 seconds, the engine speed in 2nd gear must be 130 RPM less than the last engine speed in 1st gear.

#### Case 2

- | The PCM commands a 2-3 shift.

- | The throttle position is 10-55% and constant by 10%.

- | The vehicle speed is 40-89 km/h (25-55 mph).

- | Within 2.5 seconds, the engine speed in 3rd gear must be 130 RPM less than the last engine speed in 2nd gear.

#### Case 3

- | The PCM commands a 3-4 shift.

- | The throttle position is 5-40% and constant by 7%.

- | The vehicle speed is 56-121 km/h (35-75 mph).

- | Within 1.0 second, the engine speed in 4th gear must be 250 RPM less than the last engine speed in 3rd gear.

#### Case 4

- | The PCM commands 4th gear.

- | The TCC is commanded ON.

- | The throttle position is 2-40%.

- | The speed ratio is 0.68-0.82.

- | The TCC slip speed is 0-50 RPM for more than 3 seconds.

3. Select Specific DTC. Enter DTC P0751.

Has the test run and passed?

--

System OK

Go to Step 1