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A 4L80E may intermittently set DTC P1810 and exhibit harsh shifts. Freeze frame/ fail records may show the vehicle was in reverse and the P1810 set shortly after a cold start. The vehicle may also have not been started for an extended period of time. Recommendation/Instructions:
This condition may be inadvertently induced by starting the vehicle and immediately shifting the transmission into a drive range or reverse. If the PCM does not see a PRND43 input from the transmission fluid pressure switch before the customer shifts into a drive range or reverse, the PCM will assume the TFP is malfunctioning because the PCM did receive a signal from the PRND43 switch and set the code P1810. This condition would occur more easily if the vehicle has not been started for an extended period of time because of torque converter drain back. DTC P1810 does not turn on the MIL the first failure, but does store the code and it commands maximum line pressure. The customer will probably notice only the harsh shift.
Currently, there is no fix for this condition. The dealer can advise the customer to start the vehicle and allow it to run for a few seconds before selecting reverse or selecting D4 before reverse.