Check engine light or Adblue warning with fault codes P206B31,
P203B31, or P300494 present in AdBlue (SCR) control unit (N118/5)
Topic number

LI49.20-N-078838

Version

10

Function group

49.20 - Exhaust gas aftertreatment

Date

2/24/26

Validity

Model 907

Reason for change

Remedy Update

Complaint
The check engine light or AdBlue warning is activated, accompanied by one or more of the following fault codes related to the AdBlue tank:
P206B31: Malfunction of the concentration sensor for AdBlue; the signal is absent.
P203B31: Malfunction of the AdBlue fill level sensor; the signal is absent.
P300494: The quality of the AdBlue is insufficient.

Cause
A. The software for the AdBlue (SCR) control unit (N118/5) is outdated.
B. The concentration of AdBlue is either above or below the Mercedes-Benz specifications, which can lead to premature freezing.
C. Frozen or partially frozen AdBlue can cause the AdBlue level sensor to misread levels.
D. The AdBlue level sensor is damaged.

Remedy
A. Software
1. Verify no newer software in AdBlue® SCR control unit (N118/5).
2. Complete LI49.20-N-075995 for Adblue warning reset.
--NOTE-- If there is no updated software available, print the XENTRY screen indicating this and proceed to step B.
B. Adblue Concentration
1. Verify the AdBlue concentration
a. According to WIS AR49.20-D-9264TS - Check the concentration of AdBlue
b. Per the freeze frame data 'Development data (Urea Qualitaet Rohwert)', see attachment 'Urea Quality'.
--NOTE-- If the AdBlue concentration is below 31.8% or above 33.2%, it must be replaced. Please note that this will
be at the customer's expense.
2. If the AdBlue concentration is within the approved specifications, please proceed to step C.
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C. Frozen Adblue or the SCR Actual Values state 'Frozen Adblue'
1. Check if the AdBlue is frozen. If it is, let the vehicle sit in a warm place overnight and recheck.
2. Have the vehicle running and XENTRY hooked up displaying Adblue level values
3. Drain the Adblue Tank and verify fill level reflects the change in the Adblue level
4. Fill the AdBlue tank slowly. Do not overfill. Verify that the fill level reflects the change in AdBlue level. Print the
XENTRY Actual Values page showing the AdBlue tank in the Empty, Full, and refilled Full states.
--Note-- For MY23-25, Fill Level Sensor 1 functions as the empty sensor. It accurately measures only the bottom 60
mm 2.3 inches of the AdBlue tank. Once the tank level is above 60 mm 2.3 inches, the sensor may no longer read accurately and the displayed value may fluctuate. This is normal. See attachment “Fill Level 1.”
--Note-- As of model year 2026, only Fill Level 2 is displayed in XENTRY Actual Values.
5. Reset the Adblue Tank fill level via XENTRY. Please print the XENTRY pages that indicate the AdBlue tank fill-up
was completed successfully.
--NOTE-- If the XENTRY still shows that there is frozen Adblue or the concentration is still inaccurate after draining
and filling, please refer to the attachments 'Adblue Frozen' and 'Adblue Concentration' and proceed to step D.
6. Complete LI49.20-N-075995 for Adblue warning reset. Please print the XENTRY pages that indicate the AdBlue
warning reset was completed successfully.
--NOTE-- If the steps above do not fix the vehicle, please proceed to step D.
D. Damaged Adblue Level Sensor/Concentration Sensor
1. Replace the Adblue Tank
2. With the vehicle running and XENTRY hooked up displaying Adblue level values
3. Fill the Adblue Tank SLOWLY and do not overfill, verify fill level reflects the change in the Adblue level
3. Reset the Adblue Tank fill level via XENTRY
4. Complete LI49.20-N-075995 for Adblue warning reset.
--NOTE-- During LI49.20-N-075995 for Adblue warning reset, please ensure that the outside temperature sensor
is reading above 10 degrees Fahrenheit. If it is not, keep the vehicle inside the shop overnight. Complete LI49.20N-075995 again. Additionally, please note that the vehicle may need to be driven to allow the NOx sensors and SCR
system to complete their self-test. Once this is finished, the P13DF00 code should be stored and can then be cleared.
--NOTE-- During cold weather, when temperatures are below 32 degrees Fahrenheit, please advise the client to keep
the AdBlue tank fill level between 50% and 85%. This will allow for proper fluid expansion and help prevent damage to
the level/concentration sensor.

Attachments
File

Description

Adblue Frozen.png

Adblue Frozen

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Adblue Concentration.png

Adblue Concentration

Adblue Fill Level.mp4

Adblue Fill Level 1

Urea Quality.png

Urea Quality

WIS-References
Document number

Title

Note

AP49.20-D-0101TS

AdBlue(R) tank - Check/correct fluid
level

AR49.20-D-2015TS

Empty/fill AdBlue(R) tank

AR49.20-D-2014TSF

Remove/install AdBlue(R) tank

Disclaimer

NOTE: The information contained in this document is intended for use by trained, professional technicians with the
knowledge to properly and safely perform diagnosis and repairs on Mercedes-Benz vehicles, using Mercedes-Benz
approved tools and equipment. It informs service technicians about conditions that could occur in certain vehicles and
provides information that could assist in proper vehicle diagnosis, service, or repair. It does not indicate that a defect
is present in any vehicle referenced in this document nor does it imply warranty coverage. DO NOT assume that a
symptom or condition, or a described cause of a symptom or condition, affects any particular vehicle or groups of vehicles, or that a described repair applies to any particular vehicle or groups of vehicles. There can be multiple causes
resulting in the same or similar symptoms or conditions described in this document, and trained professional service
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technicians must use their diagnostic skills to make evaluations on a case-by-case basis. The information contained
in this document does not guarantee warranty coverage nor does it extend the vehicle’s warranty in any way.

Symptoms
Power generation > Fuel system > Fuel tank > Function > Different level
Power generation > Exhaust system > AdBlue > AdBlue consumption > Too high

Parts
Part number

ES1 ES2 Designation

A9104702401

Quantity Note

NOX REDUCING AGENT
TANK

EPC

1

X

Control unit/fault code
Control unit

Fault text

N118/5 | N141 - Selective catalytic reduction (SCR
GEN4) (UDCM2)

P203B31 - The AdBlue® fill level sensor has a malfunction. The signal is not present.
P206B31 - Concentration sensor 'AdBlue®' has a malfunction. The signal is not present.

N3/40 - Motor electronics 'MRD1' for combustion engine
'OM654' (CDI) (MRD1NFZ)

P300494 - The AdBlue® quality is insufficient.

Operation numbers/damage codes
Op. no.

Operation text

470643

Check separate parts of AdBlue(R) sys- 0.7 H
tem: ... as per fault code

499264

Check AdBlue(R) concentration (After
quick test)

H

499290

Empty/fill AdBlue(R) tank

H

499292

Replace AdBlue(R) tank

H

540650

On-board power supply voltage Maintain H
(when checking/testing and troubleshooting)

540990

Program, code ..... control unit (After
quick test)

H

541011

Perform quick test

H

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Time

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Damage
code

Note
This Operation item is used for completing LI49.20-N-075995.

4707250

If newer software is available

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