P0751

Diagnostic Chart:

Wiring Diagram:

Circuit Description

The 1-2 Shift Solenoid Valve (1-2 SS Valve) controls fluid flow acting on the 1-2 shift valve and the 3-4 shift valve. The 1-2 SS Valve is a normally-open exhaust valve. Used with the 2-3 Shift Solenoid Valve (2-3 SS Valve), the 1-2 SS Valve allows four different shifting combinations.

If the PCM detects a 1-1-4-4 only or a 2-2-3-3 only shift pattern, then DTC P0751 sets. The pattern that the PCM detects depends on the mechanical failure. DTC P0751 is a type A DTC.

Conditions for Setting the DTC
- No Throttle Position Sensor (TPS) DTCs P0122 or P0123
- No Vehicle speed Sensor (VSS) DTCs P0502 or P0503
- No Torque Converter Clutch (TCC) Stuck ON DTC P0742
- No 1-2 SS Valve DTC P0753
- No 3-2 SS Valve Assy. DTC P0785.
- No TCC Sol. Valve DTC P0740.
- No TCC Pulse Width Modulated (PWM) Sol. Valve Assy. DTC P1860.
- No 2-3 SS Valve DTC P0758
- No TFP Val Position Sw. DTC P1850.
- Previous shift time is greater than 0.0 seconds.
- The gear range is D4.
- The engine speed is greater than 400 RPM for 5 seconds and not in fuel cutoff.
- The vehicle speed is greater than 8 km/h (5 mph).
- Transmission temperature is 20-130°C (68-26° F).
- All the above conditions have been met and the combination of Cases 1,2,3, and 4 or Cases 1,2,3, and 5 occur three consecutive times.

Case 1
- Commanded 1-2 shift
- The TP angle is 10-45%.
- The TP angle is constant within +/-6%.
- Vehicle speed is 8-72 km/h (5-45 mph).
- Within 2 seconds, the engine speed in 2nd gear must be 100 RPM greater than the last speed in 1st gear.

Case 2
- Commanded 2-3 shift
- The TP angle is 3-45%.
- The TP angle is constant within +/-10%.
- Vehicle speed is 16-105 km/h (10-65 mph).
- Within 2 seconds, the engine speed in 3rd gear must be 100 RPM less than the last speed in 2nd gear.

Case 3
- Commanded 3-4 shift
- The TP angle is 2-45%.
- The TP angle is constant within +/-7%.
- The vehicle speed is 48-105 km/h (30-65 mph).
- Within 0.7 seconds, the engine speed in 4th gear must be I RPM greater than the last speed in 3rd gear.

Case 4
- Commanded 4th gear
- The TCC is ON.
- The TP angle is 7-35%.
- The speed ratio is 0.95-1.2 (the speed ratio is the engine speed + the output speed).
- The TCC slip speed is 200-1000 RPM for greater than 4 seconds.

Case 5
- Commanded 4th gear
- The TCC is ON.
- The TP is 7-35%.
- The Speed ratio is 0.65-0.8 (the speed ratio is the engine speed + the output speed).
- The TCC slip speed is -20 to 40 RPM for greater than 4 seconds.

Action Taken When the DTC Sets
- Use D2 pressure schedule
- The PCM inhibits 3-2 downshifts if the vehicle speed exceeds 48 km/h (30 mph).
- The PCM illuminates the Malfunction Indicator Lamp (MIL).

Conditions for Clearing the MIL/DTC
- The PCM turns OFF the MIL after three consecutive ignition cycles 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
- Verify that the transmission meets the specifications in the Shift Speed.
- Refer to Shift Solenoid Valve State and Gear Ratio.
- More than one shift may occur because of other internal transmission failures.

Test Description

The numbers below refer to the step numbers on the diagnostic chart.
2. This step verifies that the TFP Valve Position Switch is functioning normally.
3. This step verifies that the following sequence occurs:
- The scan Tool commands all shifts.
- All the shift solenoids respond properly.
- Not all the shifts occur.