Keyless entry doesn't work on my 03 c230 coupe

have you changed the battery in your remote?

Do you have multiple keyless entries for this car? If so does the other one still work, perhaps it just needs to be reprogrammed. Take it to your nearest Honda dealer and they should be able to get it working again. If it is constantly locking and unlocking, the computer could be getting a signal from the remote which would indicate a reprogramming is needed too.

Please let me know how this goes.

Testing would need to be done , scan tool hooked up checking DTC'S - diagnostic trouble codes . View data etc...
Keyless Entry System Description and Operation - Active
The keyless entry system is a vehicle entry device. The keyless entry system is used in conjunction with the door locks to unlock the vehicle. Keyless entry will lock/unlock a door or open the rear compartment lid when a corresponding button on the keyless entry transmitter is pressed. This is accomplished by the transmitter sending a radio frequency to the remote control door lock receiver (RCDLR). The RCDLR interprets the signal and activates the requested function via a serial data message. A low transmitter battery or radio frequency (RF) interference from aftermarket devices, such as 2-way radios, power inverters, computers, etc., may cause a system malfunction. High RF traffic areas, such as gas stations that use pay-at-the-pump RF transponders, may also cause interference that could lead to a malfunction. Keyless entry allows you to operate the following features:
• Door lock/unlock
• Rear compartment lid release
• Illuminated entry lamps
• Panic alarm/Vehicle locator
• Remote vehicle start

Your best bet , take it to a qualified repair shop . Dealer

does your unlock button work in car? If it does, do you have another keyless entry key fob? If so does it work? If you just replaced the battery you can try removing battery and cleaning contacts within remote. I know some of the nissan altimas had the same issue and the only solution was a new key fob. Good Luck

If the system is not working even when you press the buttons on the door, then the problem is not with the remote control. I would first check if all the fuses are ok, if they are, I would check the wiring on the door to make sure there are no wires broken of chaffed. Focus first on getting the system working with the door buttons and after that is ok, the move on to the keyless system in case it still does not work. Hope this helps.

Have you tried to change the batteries again?

Hello: To resynchronize the keyless entry close all doors, key out of ignition. Hold lock and unlock buttons till the doors (all) lock then unlock. If the transmitter still doesn't work you have other problems. Go to auto zone they can check your transmitter to see if it is working.

have remote checked out at advance auto,could be ur keyless entry sensor bad

It wouldn't be the car battery, but since you just purchased the car, the dealership should correct the problem. Bring it to their attention right away. Did you get any kind of warranty? Most dealers have at least a 30 day warranty for things like this.

Lock all the doors from the inside (with all the doors closed), unlock your driver's door by manually lifting the lock, then press it back down after you are out - this will prevent the alarm from sounding when you use the key to unlock the door.