OBD-II code family
Software Incompatibility With Active Grille Air Shutter Module (U034E–U0351)
4 codes describing the same fault on 4 enumerated slots. The letter is the index your manufacturer assigned — it is not a physical difference, and it does not carry across makes.
What these codes mean
Active grille shutters are the movable vanes behind a vehicle's front grille. They close at speed to reduce aerodynamic drag and improve fuel economy, and open when the engine or the air conditioning condenser needs airflow. A small control module drives them and reports position back to the powertrain network.
These codes say that module's software does not match what the rest of the vehicle expects. Nothing is physically broken — the shutters may well still be moving correctly. Two modules are simply running software versions that were never validated together, and one has flagged it.
That makes this a service-history question rather than a diagnostic one. The usual causes are a shutter module replaced with a unit at a different software level, an update campaign applied to some modules but not others, or a used part fitted without being brought to the vehicle's software specification.
The letter A through D indexes which shutter module on vehicles using more than one, typically upper and lower grille assemblies on vehicles with split openings.
The fix is programming rather than parts. Identify the current software level in each affected module, compare against the manufacturer's specification for the VIN, and reprogram the mismatched unit. Replacing a shutter assembly in response to a software incompatibility code produces a new part running the same wrong software.
Severity is genuinely moderate here, which is worth saying plainly because the code sounds alarming. A shutter fault will not strand you. Left alone it costs a small amount of fuel economy and, if the shutters stay closed when they should open, can contribute to higher coolant temperatures during sustained hard work such as towing on a long grade. Worth fixing, not worth panicking about.
Which air shutter module is mine?
There is no generic answer, and any source that gives you one is guessing. The letter is assigned by the vehicle manufacturer, and the same letter refers to different physical components on different makes — sometimes on different model years of the same vehicle. The only authoritative source is the wiring diagram or service information for your exact year, make, model and body style.
A manufacturer-specific definition always outranks the generic one. If your make publishes its own meaning for this code, use that and ignore the generic description.