I fixed 4x4 low on my truck and thought I’d share the solution in case it helps anyone else.

Symptoms:

• 4x4 low would not engage.
• 4x4 high worked perfectly.
• Truck would start in neutral, so the DTR sensor was reading neutral correctly.
• Brake lights worked, so the brake switch was working.

Root cause: corrosion in the DTR connector. Some of the contacts were fine, but the one for the neutral signal going to the 4x4 module was corroded. The DTR sensor is mounted to the driver’s side of the transmission.



A little off/on/off/on action, electronics cleaner, and dielectric grease fixed it right up.

This diagram was invaluable for figuring out what I needed to check. Thanks to whoever posted that.

Before getting to the solution I also eliminated the 4x4 module, shift motor, and wiring as the cause by trying new parts and checking continuity.

I have an ‘04 Ranger but I imagine this could happen to any truck with a DTR sensor on the transmission. It’s pretty exposed to mud and water.

I did some research beforehand and didn’t see this mentioned anywhere, but I apologize if this is common knowledge and I just missed it.