A little assist here please,
1. 2003 2500 5.9 HO Turbo
2. 234K
3. both batteries 5 years old
4. all lights work and headlights dim and bright
5. throws codes:
P2607 after cleaning all battery cables and leads
P2609 before cleaning battery posts and leads
now throws both codes

turns on and will not crank, like the alarm ignition cut off is on, tried jump starting also.

worked fine yesterday, notice no problems when parked, went out today will not crank, batteries are fine, any suggestions appreciated

would bad heater grid relays cause the no crank?

 

Make sure you have the ground wire connected at the left side battery, it grounds the ECM on the side of the block. If not connected ECM has no ground. Engine will not start or crank with it off. If connected try disconnecting both ground from both batteries and letting sit for 10 minutes or more then reconnect. That will rest the WIN module for alarm.

 

What about the starter?

 

Make sure your truck is all the way in park...

 

No way 5 year old batteries are "fine", load test them single not parallel. Low battiries will diagnose with a ton of odd gremlins, just like you are having. Batteries are causing your issue, FTW.

Good luck.