DTC Advanced Diagnostics: P0731
DTC P0731:1st Gear Incorrect Ratio

General Description
To engage 1st gear, line pressure is supplied to the 1st clutch piston, engaging the 1st clutch, and the secondary shaft and the secondary shaft 1st gear are connected and revolve together. Hydraulic pressure is supplied to the 1st clutch through the ATF strainer ? the ATF pump ? the main regulator valve ? the manual valve ? the shift valves ? the feed pipe ? the 1st clutch piston. (A shift valve failure in the supply route above is detected by the malfunction detection of each shift solenoid valve.) The powertrain control module (PCM) computes the ratio of the input shaft (mainshaft) speed to the output shaft (countershaft) speed. When the ratio is not the 1st gear ratio, the PCM detects a malfunction of the hydraulic circuit or the 1st clutch and stores a DTC.

Monitor Execution, Sequence, Duration, DTC Type, OBD Status
Execution
Continuous
Sequence
None
Duration
12 seconds or more
DTC Type
Two drive cycles, MIL off, A/T gear position indicator blinks
OBD Status
PASSED/FAILED/NOT COMPLETED (STILL TESTING)

Enable Conditions
Condition
Minimum
Maximum
Engine speed
[ENGINE SPEED]
500 rpm
–
Vehicle speed
[VEHICLE SPEED]
8 mph (12 km/h)
–
Battery voltage
[BATTERY VOLTAGE]
11 V
–
Shift lever position
D, S
No active DTCs set (prevents monitor from running)
P0117, P0118, P0122, P0123, P0222, P0223, P0705, P0706, P0716, P0717, P0718, P0721, P0722, P0723, P0729, P0732, P0733, P0734, P0735, P0746, P0747, P0751, P0752, P0756, P0757, P0761, P0762, P0776, P0777, P0796, P0797, P0962, P0963, P0966, P0967, P0970, P0971, P0973, P0974, P0976, P0977, P0979, P0980, P1658, P1659, P1683, P1684, P2101, P2118, P2122, P2123, P2127, P2128, P2135, P2138, P2176, P2714, P2720, P2721
[ ]: HDS Parameter

Malfunction Threshold
The actual gear ratio must match one of these conditions for at least 12 seconds with the 1st gear command:
Actual gear ratio is greater than the 1st gear ratio by a factor of 1.25.
Actual gear ratio is less than the 1st gear ratio by a factor of 0.8.

Possible Cause
NOTE: The causes shown may not be a complete list of all potential problems, and it is possible that there may be other causes.
Shift control system failure
1st clutch disc surface worn
ATF pump flow pressure insufficient

Confirmation Procedure
Operating Condition
1.
Start the engine.
2.
Drive the vehicle in D at a speed of 8 mph (12 km/h) or more for at least 12 seconds in 1st gear.
Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.
With the HDS
None.

Diagnosis Details
Conditions for setting the DTC
When a malfunction is detected during the first drive cycle, a Pending DTC is stored in the PCM memory. If the malfunction returns in the next (second) drive cycle, the A/T gear position indicator blinks and a Confirmed DTC and the freeze data are stored. The MIL does not come on.

Conditions for clearing the DTC
The A/T gear position indicator comes off by pressing the engine start/stop button to select the OFF mode. The Pending DTC, the Confirmed DTC, and the freeze data can be cleared with the scan tool Clear command.