P0731

Diagnostic Chart:

During normal driving modes the PCM/TC adapts line pressure to prevent clutch slip and harsh shifts. If 1st clutch is slipping after pressure is adjusted to high line, it is determined that there is no 1st gear. First gear clutch is fed directly from the manual valve and is always applied in all forward gear selections.

DTC PARAMETERS
DTC P0731 will set when the PCM has detected the following twice in an ignition cycle:
- Vehicle speed is greater than 5 km/h (3 mph).
- Input shaft speed is greater than 224 rpm.
- No input shaft or vehicle speed signal noise.
- High line pressure has been commanded.
- Ratio failure counter equals 255 for an in-gear failure, or the shift failure counter is greater than 100 on a downshift to 1st during acceleration (128 = 0 or normal operation);
or
Second gear must be commanded On for the vehicle to move.

TEST DESCRIPTION
Numbered steps below refer to numbered steps on chart.
1. Check for DTCs P0745, P0716 and P0717. They must be eliminated first as a possible cause for DTC P0731 - No first gear.
2. Pressure test at the same temperature that fault occurred to assure the fault is not a pressure problem that only occurs in a particular temperature range. Low line pressure, which would be indicated by DTC P0745 line pressure low must be eliminated first as possible cause for DTC P0731 - No 1st Gear.
3. Refer to "Test Section Diagnosis" in the "Automatic Transaxle Service Manual" for pressure apply points. Remove valve body and air check 1st clutch apply through case passage.
4. This step targets the specific mechanical failure.

Clutch Leaks:
- Remove end cover and check for damaged 1st gear hub seal rings and check for blocked passage in cover or case.
- If seal rings are OK, remove 1st clutch and replace leaking piston.
- Servo leak causing loss of 1st oil pressure. Remove valve body and air check and check 1st oil pressure passage to servo. Also, check 1, 3, 4 passages to servo.

No Blockage in Passages:
- 1st gear sprag failed.
- 1st clutch plates failed as a result of low line pressure or inadequate lube.
- Output shaft broken.
- Incorrect gear ratio installed.

REPAIR VERIFICATION
Monitor DTC menu "Code Status" for "Pass Since Code Clear" and "Pass This Ignition Cycle." When both have passed, repair is verified.

Criteria for pass: steady in 1st gear with no slip for 0.4 seconds and engine torque is greater than 30 counts for 0.1 seconds.

DIAGNOSTIC AIDS
- To air check 1st clutch, use 1st clutch pressure port in test section. Apply compressed air, with rubber nozzle on air gun.

IMPORTANT: 1st gear is a mechanical hydraulic apply. Other than line pressure there is no electrical circuit that affects this gear.

- DTC P0731 - No 1st gear, may be set under certain conditions if an intermittent loss of vehicle speed signal occurs. If customer is also experiencing speedometer problems check the VSS circuit as a possible cause of DTC P0731.
- A short-to-ground or open in the turbine speed sensor wiring will set DTC P0731. Verify using Scan tool.
- Verify proper calibration installed in PCM.