P0731
The PCM uses the Crankshaft Position (CKP) sensor, Transaxle Input Speed Sensor (ISS) and Vehicle Speed Sensor (VSS) to determine engine speed, input shaft speed and output shaft speed. These sensor readings are used to determine the current gear ratio and RPM slip across the torque converter. The PCM uses this information from the sensors to determine if the commanded gear matches the actual gear. During normal driving conditions, the PCM will adapt main line pressure via the pressure control (PC) solenoid to prevent slipping and harsh shifts. First gear clutch is fed fluid directly from the manual valve and is applied in all forward gears. DTC P0731 sets when 1st clutch still slips after the PCM has commanded high main line pressure.
DTC PARAMETERS
DTC P0731 will set if the PCM detects an incorrect actual 1st gear ratio when 1st gear is commanded On when:
- Condition exists twice in one ignition cycle
- High main line pressure has been commanded
- Transaxle is in a forward gear
- Transmission ISS is greater than 224 RPM
- Vehicle speed is greater than 5 km/h (3 mph)
- Speed noise parameter = NO
- Steady state ratio fail counter equals 255 for an in-gear failure, or the shift fail counter is greater than 100 on a downshift to 1st during acceleration (128=0 or normal operation)
OR
- Condition exists twice in one ignition cycle
- Second gear must be commanded On for the vehicle to move.
DTC P0731 diagnostic runs continuously once the above conditions have been met.
DTC P0731 is a type A DTC.
DIAGNOSTIC AIDS
IMPORTANT:
- If DTC P0745, P0746, P0756, P0758, P0761, P0763, P0766, P0768, or P0789 is set, diagnose that DTC first. A diagnosed PC solenoid, shift solenoid 2, 3 or 4 low/high circuit fault DTC may have caused DTC P0731 to set.
- If a shift solenoid performance 2, 3 or 4 DTC (2nd, 3rd or 4th gear stuck On) is set, diagnose the highest gear first. A gear stuck On will cause no 1st gear.
Refer to "Test Section Diagnosis" for pressure apply points and for the following component/location description.
Possible causes of no 1st gear:
- End cover first gear hub seal rings damaged
- 1st clutch piston leaking
- Input shaft feed tube to end cover blocked
- Servo leaking or passages blocked causing no oil pressure to 1st clutch
- 1st gear sprag failed
- 1st gear clutch plates worn
Verify VSS and TRANSMISSION ISS read correctly on Scan tool.
Make sure the pressure control, shift 2, shift 3 and shift 4 solenoids are not intermittently sticking. Sticking solenoids may cause 2nd, 3rd or 4th gear to be applied from an initial start causing no 1st gear. Audible sound should be similar for all solenoids. A muffled tone indicates the need for replacement.
IMPORTANT: 1st gear is a mechanical hydraulic apply. Other than line pressure, there is no electrical circuit for 1st gear.