My key seems to have lost it's coding.
I noticed when it no longer worked as a remote door locker, or unlocker.
When I try to start, it turns over, runs for a second and stops.
The red security light (it doesn't have an alarm) flashes When the ignition is turned on.
I live a long way from the nearest dealer (100 miles).
Do I need to replace the key, or can the dealer re-program it, or what?

 

Don't know if this will help. If you have the big combined key/door remote, have you tried replacing the battery in it?

My wife's Durango (with only 27K on the dometer) has needed the battery changed twice to open the doors remotely since we bought it in 2004. I never thought to try to see it it will still start the Durango with the dead battery in it. I just drove out and gave her my key which she started it with and drove with until I replaced the battery in hers.

 

Battery replacement time.

 

Dodge truck keys are coded even though they look like ordinary keys. I have 2 coded keys and 1 non coded key. The non coded key will turn the motor over but it will not start. I use this key to lock my doors while I leave my truck running sometimes.

Anyway, yes you will need to get another coded key. I wouldn't reuse that old key just in case. They are pretty pricey at my dealership, around $175, let us know what you payed for your new one.

 

If you haven't replaced the battery in the remote I'd do that first.

 

Sorry, my fault, I should have mentioned that I changed the battery, already.
I took it to the dealer when I was in town, which is a 100 mile one way trip for me.
The guy in Service looks at it, brings a signal detector out which shows that the key is emitting signal at full strength, so he says, 45 bucks to re-code the key.
I said, "Later", and left.
I just got a call in response to my email to the dealer, bring it back (remember 200 mile round trip), the key is under warrantee. I could kick that guy at the service desk, and may when I see him.
I will opt for a new key, rather than merely re-coding.
I will also get a spare, if possible.
The manual shows a method for coding a spare key yourself, but you have to have TWO keys.
So, when I go back to town in two weeks, I will stop in.