P0729

A760H AUTOMATIC TRANSMISSION: ELECTRONIC CONTROLLED AUTOMATIC TRANSMISSION SYSTEM: P0729: Gear 6 Incorrect Ratio
P0729 - Gear 6 Incorrect Ratio

DESCRIPTION

The ECM uses signals from the output speed sensor SP2 and input speed sensor NT to detect the actual gear position (1st, 2nd, 3rd, 4th, 5th or 6th gear). Then the ECM compares the actual gear with the shift schedule in the ECM memory to detect mechanical problems of the shift solenoid valves, valve body or automatic transmission (clutch, brake or gear, etc.).









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






- Gear position during fail-safe operation:
If any malfunction is detected, the ECM changes into the fail-safe mode to shift into the gear positions as shown in the table below.






MONITOR DESCRIPTION

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 DTC indicates that the sequence valve is locked in the direction the spring stretches and that shifting to the 6th gear is impossible.

MONITOR STRATEGY





TYPICAL ENABLING CONDITIONS

The following items are common to all conditions below.





Condition (A)





Condition (B)





TYPICAL MALFUNCTION THRESHOLDS

Both of the following condition are met: Condition (A) and (B)

Condition (A)





Condition (B)





INSPECTION PROCEDURE

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

PROCEDURE

1. CHECK OTHER DTCS OUTPUT (IN ADDITION TO DTC P0729)

(a) Connect the Techstream to the DLC3.

(b) Turn the engine switch on (IG) and push the Techstream main switch ON.

(c) Enter the following menus: Powertrain / ECT / Trouble Codes.

(d) Read the DTCs using the Techstream.

Result:





HINT
If any other codes besides P0729 are output, perform troubleshooting for those DTCs first.

B -- GO TO DTC CHART
A -- Continue to next step.

2. PERFORM ACTIVE TEST USING TECHSTREAM (RUNNING TEST)

HINT
Performing the Techstream Active Test allows relay, VSV, actuator and other items to be operated without removing any parts. Performing the Active Test early in troubleshooting is one way to save time.

The Data List can be displayed during the Active Test.

(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 / ECT / Active Test.

(g) Perform the Active Test using the Techstream.

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

Comparing the shift position commanded by the Active Test with the actual shift position enables you to confirm the problem Fail-Safe Chart.

ECM:





HINT
- This test can be conducted when the vehicle speed is 50 km/h (31 mph) or less.
- The 4th -> 5th and 5th -> 6th up-shiftings must be performed with the accelerator pedal released.
- The 6th -> 5th and 5th -> 4th down-shiftings 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 (Shift Status) display on the Techstream.
- Gear positions in the event of a solenoid valve mechanical problem:






OK:

Gear position changes in accordance with the tester command.

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

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





NOTICE:
- Perform the test at the normal operating ATF temperature: 50 to 80°C (122 to 176°F).
- Be careful to prevent SST's hose from interfering with the exhaust pipe.
- Perform the test with the A/C OFF.

HINT
Performing the Techstream Active Test allows relay, VSV, actuator and other items to be operated without removing any parts. Performing the Active Test early in troubleshooting is one way to save time. The Data List can be displayed during the Active Test.

(a) Remove the test plug on the transmission case center right side and connect SST.

SST : 09992-00095

09992-00231

09992-00271

(b) Connect the Techstream to the DLC3.

(c) Start the engine and warm it up.

(d) Measure the line pressure with SST.

(e) Turn the Techstream ON.

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

(g) Follow the instructions on the tester and perform the Active Test.

(h) Measure the line pressure with SST.

ECM:





HINT
- *: Activate the Solenoid (SLT) in the Active Test is performed to check the line pressure change by connecting SST to the automatic transmission, which is used in the HYDRAULIC TEST Hydraulic Test.
- The pressure values in the Active Test and HYDRAULIC TEST are different from each other.
- Normally, the line pressure detected in the Active Test is approximately half of the value detected in the HYDRAULIC TEST's stall test.

OK:

The line pressure changes as specified when performing the Active Test.

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

4. CLEAR THE DTC AND RUNNING TEST

(a) Clear the DTC, and check for DTCs again after conducting the "MONITOR DRIVE PATTERN FOR ECT TEST" Monitors, Trips, Drive Cycles and Readiness Codes.

OK:

No DTC code

NG -- REPAIR OR REPLACE TRANSMISSION VALVE BODY ASSEMBLY

OK -- END