With the wear of the clutch plates and brake bands in the automatic transmission, the change of the spring force and the aging of the seals, the shifting time of the transmission will change. The PCM passes the transmission input shaft speed sensor (ISS) and the output shaft speed through the transmission. The speed change of the sensor (OSS, that is, the vehicle speed sensor VSS) is used to determine the start and end of the shift time, thereby calculating the shift time. If the upshift time is longer than the standard calibration time, the PCM reduces the current to the transmission fluid pressure control solenoid valve (PC valve) to increase the line pressure and shorten the next shift time. If the PCM detects that the gear shift time is shorter than the standard calibration time, the PCM increases the current of the transmission oil pressure control solenoid valve (PC valve) to reduce the line pressure and prolong the next shift time. After shifting, the PCM also judges the slip amount of the clutch according to the ISS and VSS signals. If excessive slip is detected, the PCM increases the line pressure by reducing the current value of the PC valve to maintain the proper gear ratio.
When the PCM is performing the shift adaptation adjustment, if it is detected that the shift time exceeds 0.65 seconds and the adaptation regulator cannot shorten this time, the counter is incremented by 1 , if the counter value is 2 during a trip, the PCM will memorize the fault code P1811. After the fault code Pl8 is memorized, the PCM will freeze the shift adaptation, command the maximum line pressure, and will not light the fault light. The fault code “DTCP1811” is a Type C fault code, and its presence does not illuminate the fault light.
Solution: It can be solved by replacing the solenoid valve and increasing the accumulator spring.