P0688 Diagnostic and Fix for 2011 Dodge Ram 1500 4X4 with 5.7 Hemi Engine
I own a 2011 Dodge Ram 1500 4x4 equipped with a 5.7L Hemi engine. While I was refueling on a slight incline, I left the truck in 4WD and turned it off. After switching back to 2WD while the engine was off, I restarted the vehicle normally. However, two hours later, when attempting to start the truck again, it kept cranking but would not ignite. The 'Service 4WD' warning light illuminated in yellow. I attempted a battery disconnect for two hours with no resolution. A diagnostic scan revealed fault code P068-than the truck was still in 4WD at shutdown. I suspect an issue with the Anti-Theft System (ASD) relay or wiring related to the 4WD system. I'm seeking advice on how to properly diagnose and resolve this P0688 error, especially since it's affecting my ability to start the vehicle and triggers a service 4WD warning.
Try removing the ASD (Anti-Theft System) relay and use a 12-volt test light connected to ground. With the key on and engine off, probe terminals 85 and 30—both should show voltage. These are fused circuits; ensure your test light is properly grounded by touching its positive terminal to the battery positive. If no voltage is present at either terminal, it may indicate a faulty ASD relay or wiring issue. Note: There are no different-colored LEDs on the transfer case switch.