After I had the head replaced, the transmission seems to always be in the Drive gear.
I'm assuming that you mean that the D4 light is lit up on the dash not that the transmission is in gear. The D4 light indicates a problem with the electrical system, and codes will need to be pulled off the computer to determine what the problem is. I would recommend having a technician come out from YourMechanic and pull the codes from the computer to determine the cause of the transmission problem. They may have knocked some wires lose to the transmission when they replaced the head that may need to be reconnected.
Have a car question? Get free advice from our top-rated mechanics.
Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Save up to 30%