If your car isn't shifting into any other gears, I would suspect the Transmission control unit
Problem with the A/T seek professional help immediately.
It means you have a problem with the transmission. Take the vehicle to a trusted transmission professional for repair.
There is a problem with the transmission and you need to get it to either honda or a mechanic.
Transmission error
The D4 light on a Honda Accord is the transmission warning light. These come on when there is a malfunction on the transmission. For the problem to be diagnosed properly the vehicle should be taken to a dealership.
it means your motor is about too shut down and or is overheating.
It's the transmission computer.you need to replace it.
transmission trouble for sure
Replace your AT Control Unit (Automatic Transmission Computer)
A flashing D4 light on Honda Accords is commonly the result of a bad speed sensor. The speed sensor is located on the transmission and sends a signal to the speedometer and a signal telling the transmission when to shift.
The D4 light on a Honda Accord is the symbol for the 'check transmission' light. This light appears when the computer senses something wrong in the drivetrain. The computer should be diagnosed at a proper repair shop in order to source out what exactly is causing the problem.
Code 12 is a faulty EGR valve. You need to clean or replace the EGR valve of all carbon. The exhaust passage on which the EGR is mounted needs to be cleaned of carbon deposit as well. The flashing D4 light indicates a transmission problem. This needs to be looked at by a professional.