DCS grills, side burners, outdoor refrigeration and the outdoor warming drawer mostly run on mechanical controls — knobs, valves, an igniter module — rather than a digital display, so diagnosis starts with what can be observed directly: whether the igniter clicks and sparks, whether the flame is blue or yellow, whether gas can be heard or smelled at the burner, whether a compressor is cycling. That is often faster than waiting on a code, but it means describing what you are seeing and hearing accurately matters just as much when you book.
The legacy indoor wall ovens do have an electronic control and a display, and some models will show a code or message. If yours does, write it down exactly as it appears along with the model number from the plate inside the door before calling — the model decides what the code means, and having both ready saves a visit. Either way, a suspect part is tested and shown to have failed before it is added to your estimate.