P0781

A760F AUTOMATIC TRANSMISSION / TRANSAXLE: AUTOMATIC TRANSMISSION SYSTEM: P0781: 1-2 Shift (1-2 Shift Valve)
P0781 - 1-2 Shift (1-2 Shift Valve)

DESCRIPTION

The 1-2 shift valve performs shifting to 1st gear and other gears. When shifting to 2nd and 4th gears is impossible, or when the ECM directs the transmission to switch to 5th or 6th gear and the engine overruns (clutch slips), this DTC is stored.





HINT
- Gear positions in the event of a solenoid valve mechanical problem:






N*: Neutral
- Gear position during fail-safe operation:
If any malfunction is detected, the ECM enters fail-safe mode and performs gear shifts as shown in the table below.






1st*: Under engine braking, downshifting to 1st or 2nd gear is prohibited.

MONITOR DESCRIPTION

This DTC indicates that the 1-2 shift valve in the valve body is locked with the spring compressed.

The ECM commands gear shifts by turning the shift solenoid valves ON/OFF and switching oil pressure to the valves in the valve body.

The ECM calculates the "actual" transmission gear by comparing the signals from the input speed sensor (NT) and the output speed sensor (SP2). The ECM can detect many mechanical problems in the shift solenoids, valve body, transmission clutches, brakes and gears. If the ECM detects that the actual gear position and the commanded gear position are different, it will illuminate the MIL and store the DTC.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

All





HINT
*: Following conditions are met





Condition (A)





Condition (B)





Condition (C)





Condition (D)





TYPICAL MALFUNCTION THRESHOLDS

- Both of the following conditions are met: Condition (A), and Condition (B), (C) or (D)

Condition (A)





Condition (B)





Condition (C)





Condition (D)





INSPECTION PROCEDURE

NOTICE:
Perform the universal trip to clear permanent DTCs Reading and Clearing Diagnostic Trouble Codes.

PROCEDURE

1. CHECK DTC OUTPUT (IN ADDITION TO DTC P0781)

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG).

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(e) Read the DTCs using the Techstream.

Result





HINT
If any other codes besides P0781 are output, perform troubleshooting for those DTCs first.

B -- GO TO DTC CHART Automatic Transmission System - A760F
A -- Continue to next step.

2. PERFORM ACTIVE TEST USING TECHSTREAM (RUNNING TEST)

CAUTION:
This test should always be performed with at least 2 people.

NOTICE:
- Perform the test while the ATF temperature is between 50 and 80°C (122 and 176°F).
- Perform the test with the A/C turned off.

HINT
Using the Techstream to perform Active Tests allows relays, VSVs, actuators and other items to be operated without removing any parts. This non-intrusive functional inspection can be very useful because intermittent operation may be discovered before parts or wiring is disturbed. Performing Active Tests early in troubleshooting is one way to save diagnostic time. Data List information can be displayed while performing Active Tests.

(a) Warm up the engine.

(b) Turn the engine switch off.

(c) Connect the Techstream to the DLC3.

(d) Turn the engine switch on (IG).

(e) Turn the Techstream on.

(f) Enter the following menus: Powertrain / Engine and ECT / Active Test.

(g) According to the display on the Techstream, perform the Active Test.

HINT
While driving, the shift position can be forcibly changed with the Techstream.

Engine and ECT





HINT
- This test can be conducted when the vehicle speed is 50 km/h (30 mph) or less.
- The 4th to 5th and 5th to 6th up-shifts must be performed with the accelerator pedal released.
- The 6th to 5th and 5th to 4th down-shifts must be performed with the accelerator pedal released.
- Do not operate the accelerator pedal for at least 2 seconds after shifting and do not shift successively.
- The shift position commanded by the ECM is shown in the Data List display on the Techstream.
- Gear positions in the event of a solenoid valve mechanical problem:






N*: Neutral

OK:

Gear position changes in accordance with the Techstream command.

NG -- REPAIR OR REPLACE TRANSMISSION VALVE BODY ASSEMBLY Removal
OK -- Continue to next step.

3. PERFORM ACTIVE TEST USING TECHSTREAM (SHIFT SOLENOID VALVE SLT) P0729

NG -- REPLACE SHIFT SOLENOID VALVE SLT Disassembly
OK -- Continue to next step.

4. CLEAR DTC AND PERFORM RUNNING TEST P0729

NG -- REPAIR OR REPLACE AUTOMATIC TRANSMISSION ASSEMBLY Removal

OK -- END