P0731

P0731-INCORRECT 1ST GEAR RATIO





The PCM uses the Crankshaft Position (CKP) sensor, Input Speed Sensor (ISS) and Output Speed Sensor (OSS) 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 for longer than 3 seconds (2001)*
- Condition exists for longer than 3 seconds, 1 minute is allowed to elapse, then condition again exists for longer than 3 seconds.
- High main line pressure has been commanded
- Transaxle is in a forward gear
- Input speed is greater than 224 rpm.
- Vehicle speed is greater than 5 km/h (3 mph)
- Speed noise parameter = NO
- Steady state ratio tail 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 for 2000, type B for 2001.*
* Applicable to vehicles built after June 2000.

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.

IMPORTANT: If any shift solenoid performance DTCs P0781,P0782 or P0783 (2nd, 3rd or 4th gear stuck On) are set, diagnose the highest gear first. A gear stuck On will cause no 1st gear.
Refer to Pressure Ports - Air Check for pressure apply points and for the following component/location description.
Possible causes of no 1st gear ratio:
- 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 spray failed
- 1st gear clutch plates worn

Verify TRANSMISSION ISS and TRANSMISSION OSS 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.