All with M17x - CEL ON - DTC P012800 The Coolant Temperature is Below the Specified Temperature
Topic number

LI20.10-P-072886

Version

20

Function group

20.10 - Coolant pump, coolant thermostat

Date

4/21/26

Validity

All vehicles equipped with an M17x engine

Reason for change

Re-formatting remedy section

Complaint
CEL ON with DTC P012800 "The Coolant Temperature is Below the Specified Temperature" active and stored in the
ME (N3/10). There are no drivability concerns related to the complaint.

Cause
Root cause varies

Remedy
Prior to performing any repairs for this complaint: With a cold engine, pressurize the high temp coolant circuit and while it's under pressure, release the cap on the low temp coolant circuit and check if the pressure drops right away or
not. If the pressure drops, the lower hoses are swapped. Correct this, fill, bleed and test drive the vehicle. If the complaint returns, then continue with the steps below.
IMPORTANT: Use VMI to check for emission extended warranty – Engine Thermostat (incl. software update)
MY19-23, Various Models and Platforms (167, 190, 205, 213, 217, 222, 223, 232, 253, 290, 463)
If the vehicle is covered under an emission extended warranty, Please perform steps outlined in the NCU for repairs.
If vehicle is not covered under an emission extended warranty, then proceed as follows:
Check for available software updates to the ME (N3/10). If updated software is available, perform the update, clear
the DTC and the perform each of the "WARM START" and "COLD START" test drives listed below twice. If the code
does not re-appear then release the vehicle
If there is no new software available OR the DTC returns after the test drives then perform the following steps:
•
•
•

Drain the coolant through a fine mesh sieve and check for signs of debris. Additionally, inspect the coolant reservoir for debris. If any debris is found, flush the system several times to clear as much of the debris as possible
Replace the thermostat and bleed the system as outlined in AR20.00-P-1142-04A, evacuate the system for
20-30 minutes instead of the 5 minutes specified in step 22
NOTE: Please use all the tools specified in the AR document

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© Copyright Mercedes-Benz AG

SAHARRY

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•
•

NOTE: There are two valid thermostats to choose from in the parts section of this LI. Please verify which PN is
applicable for the vehicle being worked on via XENTRY Parts Information
After bleeding the system clear the DTC and perform each of the "WARM START" and "COLD START" test drives listed below twice. If the DTC does not reappear after the tests, release the vehicle

If there is no new software available, the thermostat has already been replaced, and the DTC returns open a TIPS case and attach the following documents:
•
•
•

Initial quick test
ME (N3/10) control unit log
The results of an R48 test from a “yes” response and from a “no” response

WARM START
· Begin with the engine coolant temperature at approximately 50 degrees C
· Activate the AC system, if defrost is not in use open the windows
· Drive the car normally until a coolant temperature of 75 degrees C is achieved
· Depress the accelerator pedal 50% for ~5 seconds (partial acceleration)
· Let off the accelerator pedal and let the car coast for ~10 seconds
· Continue to drive the car normally
COLD START
· Drive for ~7 miles (normal driving)
· Shut off the engine in a parking lot (or similar), wait 30 seconds, then restart and continue driving
· Depress the accelerator pedal 50% for ~5 seconds (partial acceleration)
· Let off the accelerator pedal and let the car coast for ~10 seconds
· Continue to drive the car normally

WIS-References
Document number

Title

Note

AR20.00-P-1142-04A

Pour in coolant and bleed coolant sys- none
tem

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
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.
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© Copyright Mercedes-Benz AG

SAHARRY

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Symptoms
Power generation > Engine management > Indicator lamp > Engine diagnosis > lit

Parts
Part number

ES1 ES2 Designation

Quantity Note

EPC

A1772007901

THERMOSTAT

1

M177LS2, M177LSE

X

A1772008801

THERMOSTAT

1

M176, M177LS1, M178

X

Control unit/fault code
Control unit

Fault text

N3/10 - Motor electronics 'MED1775' for combustion engi- P012800 - The coolant temperature is below the coolant
ne 'M176/M177/M178' (ME) (MED1775)
thermostat specified temperature. _

Operation numbers/damage codes
Op. no.

Operation text

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© Copyright Mercedes-Benz AG

Time

SAHARRY

Damage
code

Note

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