If Mercedes ASSYST PLUS stays at 365 days, record the display and ask a qualified workshop to check the service data and vehicle handover status. Mercedes has documented this symptom for specified newer model series. A single reading does not establish a fault, and a frozen countdown should not be used to postpone maintenance that is otherwise due.
First check: unchanged once or repeatedly?
Take dated photographs of the same ASSYST PLUS screen, including the service description, unit and vehicle mileage. Keep the previous service invoice or, for a recently supplied car, the delivery paperwork. This gives the garage a useful comparison instead of an isolated “365” photograph.
Keep dashboard and app readings separate in your notes. If they disagree, report both rather than choosing whichever allows the later appointment. Ask the garage to establish the due date from the applicable maintenance requirements and records.
| What you observe | What to give the workshop |
|---|---|
| 365 days on one visit to the menu | The full message and date; this alone does not demonstrate a stuck counter. |
| 365 days repeatedly over time | Dated readings, mileage, delivery date and last service record. |
| A count that looks too high for the elapsed time | The earlier reading, relevant dates and any battery-disconnection history. |
| Service already due or overdue | The complete message and service history; discuss the work and appointment timing. |
The Mercedes bulletin for a permanent 365-day display
Mercedes bulletin LI00.20-P-077615, version 5, dated 1 July 2026, explicitly includes a service display permanently showing 365 days without changing. It describes uncompleted vehicle handover associated with instrument-cluster or MBUX software. Its remedy uses workshop commissioning or reinitialisation procedures that vary by model and modification year.
Its listed series are 167, 192, 206, 214, 223, 232, 236, 254, 290, 294, 295, 296, 297 and 465. A matching series is a reason to ask about applicability, not proof that your car has this condition. The document requires individual professional assessment and does not promise warranty cover.
A high day count can involve a different issue
A separate Mercedes bulletin, LI00.20-P-078424, version 3, dated 12 June 2026, addresses implausibly high remaining time relative to handover or the last confirmed service. It distinguishes battery-disconnection periods from possible loss of a day counter in the electronic ignition lock. It also directs technicians to check handover status for a permanently displayed 365 days.
This second document lists series 192, 206, 214, 223, 232, 236, 254, 294, 295, 296 and 297. It says an electronic-ignition-lock software remedy was being planned at that date. Ask the workshop for the current position; that statement does not establish that an update is available today or applies to your car.
What to ask your Mercedes specialist
- “Can you confirm my vehicle’s model series and whether either bulletin applies?” Supply vehicle identity privately.
- “Can you compare the reminder with my delivery or last-service date and explain the actual due date?”
- “Does the service data need investigation, and will you preserve an accurate record of the maintenance already carried out?”
- “What diagnostic work is included in your VAT-inclusive quotation, and is any warranty cover confirmed?”
Keep the explanation and agreed next appointment with your service documents. If maintenance is already due, discuss it separately from correcting the display. The overdue-message guide covers that booking situation.
Should I reset it or buy a scanner?
Do not experiment with service confirmation simply to make the number change. A completed service, the reminder setting and investigation of inconsistent data are separate questions for the garage. This article provides no owner reset sequence or control-unit programming instructions.
A generic OBD fault-code reader should not be assumed to diagnose or correct this specific maintenance-data problem. Before buying a tool, obtain written confirmation of the exact vehicle, software and function supported. Our diagnostic scanner guides explain how to assess coverage; no product is recommended here.
Sources and limits
Checked 9 October 2026. Both sources are Mercedes-origin technical bulletins in the US NHTSA public archive. They document particular conditions; they do not establish a UK service interval, recall entitlement or diagnosis for every Mercedes. Earlier generations require their own evidence.
- Mercedes LI00.20-P-077615, version 5, pp.1–2: permanent 365-day display, applicability, workshop remedy and limitations.
- Mercedes LI00.20-P-078424, version 3, pp.1–3: implausible remaining days, different causes and assessment boundaries.
For terminology and booking context, read ASSYST PLUS explained, what a workshop code means, and the Service A and Service B guides.
