167 with M177 and 48V System - Yellow "Coolant" message in IC
and DTC P2B2A7A The speed of the 'Coolant pump' component part
is too high. A leak or defective seal was detected stored in PTCU
Topic number

LI20.00-P-080222

Version

1

Function group

20.00 - General

Date

2/23/26

Validity

Model series 167 with M177LS2 48 V prior to model year
2024

Reason for change

General revision of remedy and cause. Check of installed
pumps omitted

Complaint
Customer states that the yellow "Coolant" message is populated in the instrument cluster.
The following DTC is found stored in the PTCU:
P2B2A7A - The speed of the 'Coolant pump' component part is too high. A leak or defective seal was detected
Notes on fault code:
The fault code concerns the right rear 15 W pump on the side of the transmission (Figure 1, position C).
The fault code concerning the speed that is too high is set because of air in the system (emergency dry run function)
IMPORTANT: This LI DOES NOT APPLY to model year 2024 and newer vehicles. For model year 2024 and newer
vehicles pump PN's A0005009100 and A0005008900 are the correct pumps

Cause
Air in the low-temperature coolant circuit

Remedy
PLEASE READ ALL THE STEPS AND FOLLOW THEM IN ORDER.
Step 1:
With the engine cold, use Xentry to activate the two pumps at the passenger front. As they are running, remove
the cap from the low temp cooling circuit reservoir and observe the coolant.
•

If it overflows the reservoir, or blows out upon removal of the cap there is a restriction somewhere in the coolant
lines.

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•
•
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This can take the form of a physical restriction inside of one of the lines or pumps or a damaged or kinked hardline or rubber hose.
Activate each pump in succession and listen to it using a stethoscope or by placing an ear to a screwdriver or
other implement placed on the pump
Compare the sound and feel of each pump. An improperly functioning, bled, or faulty pump will make a very distinct churning noise. The pumps should be near silent and should not vibrate or heat up.
If you find a pump that is making more noise than the others it is most likely pulling in air from somewhere or is
encountering a restriction (refer to the first point in this section)
If nothing of note is found, proceed to step 2.

Step 2:
Disassemble underfloor paneling and wheel well interior trim at front right to gain access to the two low temperature
pumps. Take note of or photograph the part number of the pump holder, along with the production date.
Step 3:
Check the installation position of the pumps at the front right of the low-temperature circuit (Fig. 1). Below are the correct specified part numbers at each location:
•
•
•
•

Outer: A 000 500 5500 (Fig. 1, position A)
Inner: A 000 500 3800 (Fig. 1; position B)
If installation position is NOK, continue to step 4
If installation position is OK, skip to step 7

Step 4:
Photograph the pump part numbers at the front right so that the QR-code/DMC code and the part number are visible
and legible save the pictures and label them appropriately if a TIPS case is required in the future.
Step 5:
Replace the affected pump(s) (where the installed part number differs from the specified part number, see specified
part number in step 3).
Step 6:
Use a vacuum bleeder to fill the cooling system of the low-temperature circuit.
Step 7:
Vent the cooling system of the low-temperature circuit using XENTRY.
•

NOTE: The cooling system of the low-temperature circuit is vented in various stages. To start with, the pumps at
front right are actuated at approx. 30%, then 50% and finally at 100%. At 100% actuation, the valve of the coolant circulating the pump at the side of the transmission is opened (Fig. 1; position C).

Please ALWAYS observe the following points during the venting procedure:
•
•

The front right pumps always run simultaneously. These pumps must NEVER be operated separately of each
other for actuation or for test purposes.
The pump at the rear of the transmission must run permanently after being actuated. If the pump only briefly
starts-up and then stops again, it is in a so-called emergency dry run mode because there is too much air in the
system. Please repeat the venting routine. If the rear pump at the side of the transmission remains in the emer-

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gency dry run mode, create a TIPS case, add the previously discovered findings to it and send it to the technical
support team.
If venting is successful, you will hear hardly any flow noise at all, if necessary, the venting routine may need to
be repeated several times over. If after 3 venting attempts the system still has air in it, create a TIPS case, add
the previously discovered findings to it and send it to the technical support team.

WIS-References
Document number

Title

Note

AR20.00-P-1142MNP

Drain/pour in coolant

Drain/pour in coolant

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.

Symptoms
Power generation > Engine cooling system > Indicator lamp > Illuminates yellow
Power generation > Engine cooling system > Display message > Coolant - Serviced Required

Parts
Part number

ES1 ES2 Designation

Quantity Note

EPC

A0005005500

Front right outer coolant pump, 1
low temperature circuit

X

A0005003800

Front right inner coolant pump, 1
low temperature circuit

X

Attachments
File

Description

Coolant pump locations on low temperature circuit.jpg

Figure 1

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Control unit/fault code
Control unit

Fault text

N127 - Control unit "Drivetrain" (PTCU) (CPC_NG)

P2B2A7A - The rpm of component 'Coolant pump' is too
high. Leakage or a defective seal was detected.

Operation numbers/damage codes
Op. no.

Operation text

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Time

SAHARRY

Damage
code

Note

20701**

Please refer to this TIPS document
in the dealer text

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