For 1990-2009 cars

# Harsh Shift After Cold Start - keywords DTC MIL P1810

Subject: | Harsh Shift After Cold Start

Models: | 1998-2007 Light Duty Trucks and Vans

| Equipped with a 4L80E/4L85E Transmission

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

### Condition/Concern:

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.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.