Often, the D1A code appears simply because the DEF tank was run low, and the sensor lost its reference.
If you are seeing this code, you likely pressed a specific sequence of buttons. If you want to intentionally enter this mode, follow this procedure: john deere d1a code
A: Yes, if the cause is temporary (dirty sensor reading that resolves after a regen). But if the sensor truly has invalid data, you need manual intervention. Often, the D1A code appears simply because the