The Sprinter throws a yellow lamp and a message that reads “Service AdBlue Remaining 1000 km”.
Drivers panic because the next line is always the dreaded starter lock.
The alert appears on OM651 and OM654 vans after three failed AdBlue self-tests, but nine times out of ten the fault is software rather than hardware.
This guide explains what the 1 000 km countdown means, the tools you need to clear it at the roadside, and the exact steps Mercedes outlined in its 2024 SCR bulletin for fleet technicians.
Follow the checklist and you can erase the warning in under twenty minutes without a tow or a dealer booking.
Why the 1 000 km countdown pops up
Euro-6 Sprinters run two NOx sensors.
Every 400 km the ECU compares upstream and downstream readings; if the post-cat sensor still sees high NOx, it stores one “failed monitor.”
Three failed monitors in a row and the dash throws “Service AdBlue Remaining 1000 km.”
You have roughly 620 miles before the starter motor is disabled.
The source is usually:
- Heater current zero on the post-cat sensor (open element).
- SCR dosing map corrupted after a weak battery start.
- Urea concentration too low after topping up from an open drum.
A cracked pump or clogged injector will trigger the same message, but those show P20E8 or P204F alongside the service reminder.
When the only code is P20EE, software is the prime suspect.
Roadside reset prerequisites
Before flashing anything, tick these quick checks:
- AdBlue level above 25 %. Add at least 5 L from a sealed ISO-22241 can.
- Battery voltage steady at 12.6 V or higher; hook up a booster pack if needed.
- Engine coolant above 70 °C; a ten-minute idle usually does the job.
If any of these baseline conditions are missing, the ECU blocks the reset routine and you waste key cycles.
Fast reset sequence
- Plug an ELM-327 or Autotuner dongle into the OBD-II port.
- Launch live data, scroll to NOx Sensor Heater Current (post-cat). You want 4–6 A. Zero amps means a dead sensor; change it first.
- Clear all stored and pending codes. Cycle ignition off → on.
- Start the engine, hold 1 500 rpm for 90 seconds. The ECU heats the catalyst and runs a quick AdBlue dose.
- Stop the engine, key off, wait 60 seconds. The cluster should now display distance “— — — km” then the warning disappears.
If the message persists, the SCR map checksum is corrupt.
Load the latest file from Daimler Xentry or Autotuner’s server, write in bench mode, cycle ignition and repeat the 90-second warm-up.
That clears 95 % of service reminders.
What trips people up
Using jump-leads to a running van spikes voltage and bricks the SCR ECU.
Clearing codes while the coolant is cold leaves the “Service AdBlue” line but hides the main fault — the starter lock still arrives 600 km later.
And swapping the wrong NOx sensor (upstream vs downstream) wastes £280 and two hours.
If you’re in doubt, follow the full code list in our Sprinter AdBlue fault library.
Mobile reset if the lamp won’t clear
A workshop van can flash the SCR map and code a new sensor kerb-side in 20 minutes.
Book direct on the countdown reset service line and keep the run sheet intact.
Need the warning gone before tonight’s haul?
07503 134 362 | ✉ info@adbluespecialist.co.uk
Frequently asked questions
Can I drive the full 1 000 km?
You can, but the ECU derates power after 300 km and blocks start at zero.
Will topping up AdBlue alone clear the message?
Only if low urea concentration triggered the fault. Most cases need a reset.
Do both NOx sensors cost the same?
The downstream unit is dearer—around £320 versus £190 upstream.
