U0217 is a network communication code indicating that a control module (most commonly the Body Control Module) has lost communication with 'Door Switch C' over the vehicle's data bus. It points to a problem with the switch that reports a door's open/closed state, or with the wiring and connectors between that switch and the module requesting its data. The drivetrain is not directly affected, but body-system features that depend on door status can behave incorrectly.
The switch itself (often built into the door latch assembly) has failed internally and is no longer responding on the data network, which is the single most common cause of U0217.
The harness between the body and the door flexes every time the door opens and frequently develops broken, stretched, or rubbed-through wires, producing intermittent or permanent loss of communication.
Moisture intrusion, bent pins, or a connector that has backed out of its housing can interrupt power, ground, or the data signal to the switch.
If the switch module loses its supply voltage or ground (often shared with other door electronics) it will go offline and set this code even though the switch itself is fine.
An open, short, or high-resistance fault on the data bus wires leading to the switch can prevent the BCM from hearing the switch, even when the switch is good.
The BCM is the module reporting the missing message, so it is often blamed, but internal BCM failure is uncommon for U0217 and should only be considered after the switch, wiring, and connectors have been ruled out.
In most vehicles yes. There is no direct effect on the engine, transmission, or brakes. The main risks are a drained battery if interior lights stay on, nuisance warnings, and a security system that may not arm or disarm correctly.
Not recommended. The module will usually set the same or an additional code for a missing switch, and you may lose features such as automatic locking, approach lighting, and correct alarm behavior that depend on door status.
Almost always no. The BCM is the module reporting the missing message, which makes it an easy guess, but the door switch and the door-jamb/boot wiring are far more common failures. Replacing the BCM is expensive, typically requires programming, and in the majority of U0217 cases does not fix the problem because the real fault is downstream at the switch or harness.
Generally no. U-codes are network/communication codes rather than emissions-system codes, and most inspection programs do not flag U0217 as a failure on its own. It can, however, prevent readiness monitors from completing on some vehicles if it keeps a related module from communicating.