These instructions apply to the Mercedes CLA Mk2 (C118) 2019-Present.
For other models, please choose your vehicle here.
When the wrench symbol and an “A” or “B” service message appears on your Mercedes-Benz CLA (C118, 2019–present), the ASSYST PLUS maintenance counter is due. You reset it from the instrument-cluster menu with the steering-wheel buttons — no workshop tool needed. Do the service first. This is a routine maintenance reminder counting down to the next scheduled service, not a fault or a warning that anything is wrong with the car.
What the CLA Service Message Means
ASSYST PLUS is the CLA’s flexible service system. Rather than a fixed mileage, it works out when a service is due from a mix of distance covered, elapsed time and how the car is driven — short trips, cold starts, hard acceleration and long idling all shorten the interval. As the due date approaches, the cluster first shows a countdown (a number of days or a distance remaining), then displays the wrench symbol with an ‘A’ or ‘B’ letter when the service is actually due.
The letter tells you which service package the car has calculated: an ‘A’ service is the smaller one and a ‘B’ service is the larger one, and the two normally alternate over the car’s life. The system chooses the right one for you, so all you need to do afterwards is carry out the work and reset the counter. Seeing the message does not mean the engine is unhappy — it is simply the car asking for its next planned maintenance.
Before You Begin
A reset only tells the car the maintenance has been done — it does not perform any service. Change the oil and filter (and anything else the A or B schedule calls for) before you clear the counter, otherwise the CLA will keep tracking against the old service and the next reminder will arrive too late. You need no tools for the reset itself.
- Park on level ground with the parking brake set and the car in P.
- Have the ignition on but the engine not running (see the steps below).
- Close the bonnet, boot and all doors first — the hidden menu will not arm otherwise.
Reset After the Service Only
ASSYST PLUS counts down by distance, time and driving conditions. Reset it once the oil and filter (and anything else due) are done.
How to Reset the CLA Service Indicator
- Close the bonnet, boot and all doors.
- Turn the ignition on (press start without the brake so it stays in ignition-on, not engine running).
- On the left steering-wheel touch controls, scroll to the ‘Trip’ menu.
- Hold the two control buttons together as prompted to reach the hidden ‘Workshop’ menu (VEHICLE DATA / DYNAMOMETER / ASSYST PLUS).
- Select ‘ASSYST PLUS’ → ‘Full service’ and confirm the reset.
If It Doesn’t Reset
The CLA reset is reliable once the menu conditions are right. If the counter is still showing after you finish, work through these before trying again.
- A door/bonnet is open — the menu won’t arm; close everything and retry.
- You didn’t confirm — step through ASSYST PLUS → Full service → confirm.
- The engine started — if you pressed the start button with your foot on the brake, the car is running and the reset won’t stick. Switch fully off, then press start again without the brake so it stays in ignition-on.
- You didn’t reach the Workshop menu — the two touch-control buttons must be held together long enough for the hidden menu to appear; a quick tap only scrolls the normal display.
- Cycle and repeat — switch the ignition off, wait a few seconds, switch back on and step through the menu once more.
After the Reset
Once the reset is confirmed, the wrench symbol and the A/B service message disappear and ASSYST PLUS begins a fresh countdown to the next service. The cluster no longer shows a due message at start-up, and if you open the service menu again it will report the full interval remaining. Nothing else on the dash changes — if a genuine warning light was showing alongside the service message, it will still be there and needs looking into separately.
How Often You’ll Need This
Reset the counter every time you complete an A or B service — once per service, no more. Because ASSYST PLUS is condition-based, the gap between services on the CLA varies with how and where you drive, so there is no single fixed mileage that fits every car. Let the system count down and follow the interval it calculates, and check your owner’s handbook for the maximum time limit that applies even if you cover very few miles.
Frequently Asked Questions
How do I reset the service light on a Mercedes CLA?
Via the cluster: open the Trip menu, hold the two buttons together to reach the Workshop menu, then ASSYST PLUS → Full service → confirm.
Do I need a Star/diagnostic tool?
No — ASSYST PLUS resets from the dashboard.
What do A and B service mean?
Mercedes alternates a smaller ‘A’ and larger ‘B’ service. ASSYST PLUS picks the right one; reset after whichever you’ve done.
The message came back — why?
The reset wasn’t confirmed. Repeat and confirm to the end.
Does the CLA service reset need the engine running?
No — the opposite. The ignition must be on with the engine off. Press the start button without your foot on the brake so the car powers up but doesn’t start; if the engine fires, the reset won’t take.
Is the reset the same on the CLA 250e and AMG models?
Yes — ASSYST PLUS and the cluster menu work the same way across the C118 CLA range, including the plug-in hybrid and AMG variants. Reset after whichever A or B service the car calculated.
If a warning light appeared with the service message, look it up on autodtcs.com. After battery work, see our CLA battery guide.
Independent guide — not affiliated with Mercedes. Always follow your official service manual and safety precautions. Read our full disclaimer.