Possible locations and functions:
* Differential breather: This is the most common possibility. It's a vent line that allows pressure to equalize inside the differential housing. If this is the case, it will likely be a small diameter hose. A blocked breather can cause the differential to overheat and fail.
* ABS sensor: Some ABS systems have a vent or drain line near the axle. This would likely be a very small diameter hose.
* Other components: There could be other less common vacuum lines or vents near the axle related to other systems (though less likely).
How to identify it:
1. Locate the other end: Carefully trace the hose back from where it came off. See where it appears to have been connected. This may give you a strong clue. Take pictures.
2. Diameter and material: Note the inside diameter of the hose. A small diameter hose is more likely to be a breather.
3. Check for a visible connection point: Look closely at the rear differential housing and surrounding components for a fitting that matches the hose.
4. Consult a repair manual: A repair manual specific to your 1999 Dodge Ram 2WD will show diagrams of the rear axle components and their associated hoses and lines. This is the best way to definitively identify the hose. You can often find these online (some free, some paid).
5. Online forums: Search online forums dedicated to Dodge Ram trucks. Describing the location and the hose itself (size, material etc.) might get you an answer from someone who has experienced the same issue.
Important: Do not operate your vehicle until you have correctly reconnected the hose. Driving with a disconnected breather could severely damage your differential.
