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Technical Service Bulletin

Topic

19 Engine: cooling system - engine overheats, red coolant temperature warning, MIL on - 4.0 ltr.
V8 TFSI; P029900

Market area United States 444 Volkswagen of America, Inc. (6444)

Brand Audi

Transaction 2074303/7

No.

Level EH

Status Released for publishing

Release date |Mar 18, 2025

Diagnostic trouble codes

Diagnostic address Diagnostic trouble code Fault symptom| Storage state
0001 - Engine electronics | P029900: Turbo/Super Charger Underboost Intermittent
0001 - Engine electronics | P029900: Turbo/Super Charger Underboost static

New customer code

Object of complaint Complaint type Position
engine -> cooling, lubrication -> engine coolant temperature regulation ay °

information, navigation, communication, entertainment -> instrument displays -> functionality ->

display of coolant temperature increasing

information, navigation, communication, entertainment -> warning display symbols - | functionality ->

> low coolant\coolant temperature warning display activates

information, navigation, communication, entertainment -> malfunction display functionality ->

symbols -> windshield washer system malfunction display activates

New workshop code

Object of complaint Complaint type Position

valve

engine -> cooling system -> switchable coolant pump

functionality -> does not switch
off/disconnect

valve

engine -> cooling system -> switchable coolant pump

leaks -> not watertight

Vehicle data
4.0 Itr. V8 TFSI

Sales types

Type|MY |Brand|Designation

Engine code

Gearbox code

Final drive code

* 2019/A

CXYA

*

*

* 2020/A

CXYA

*

*

Type|MY |Brand|Designation| Engine code | Gearbox code | Final drive code
* 2020|A DCUE * *
* 2020|A CWWB * *
* 2020|A DHUB * *
* 2021|A CWWB * *
* 2021|A CXYA * *
* 2021|A DCUE * *
* 2021|A DHUB * *
* 2021|A DJPB * *
* 2022|A CWWB * *
* 2022|A DJPB * *
* 2022|A DHUB * *
* 2022|A DCUE * *
* 2023 |A DWKA * *
* 2023 |A DWLA * *
* 2023|A DWNB * *
* 2023|A DWRB * *
* 2024 |A DYGA * *
* 2024 |A DWRB * *
* 2024 |A DWKA * *
* 2025|A DWRB * *
Documents

Document name

master.xml

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Technical Service Bulletin Transaction No.: 2074303/7

19 Engine: cooling system - engine overheats, red coolant temperature warning, MIL

on 4.0 Itr. V8 TFSI; P029900 Release date: Mar 18, 2025

Condition

REVISION HISTORY

Revision |Date Purpose

7 - Revised Service (Updated documenting instructions)
6 12/04/2024 | Revised Warranty (Updated accounting instructions)
5 11/06/2024 | Revised Warranty (Updated accounting instructions)

Customer statement:

+ The engine is overheating.

* The coolant temperature gauge is in the red.

* The red coolant temperature warning light appears in the instrument cluster.
and/or

+ Exhaust emissions warning lamp is on.

Workshop findings:

* The customer complaint can be reproduced, and the engine temperature is in the red. In addition, the event
memory entry P0299 (Turbo/Super Charger Underboost) may be logged in some cases.

or

+ Event memory entry P0299 (Turbo/Super Charger Underboost) logged.

Technical Background

EA825 V8 TFSI engines across all power classes are currently equipped with a switchable mechanical coolant
pump.
It is activated via the electric changeover valve N649.

When N6439 is activated, it switches a vacuum to the mechanical coolant pump. This pushes a locking sleeve over
the pump impeller, which can cause coolant to stagnate.

When N649 is not activated, no vacuum is switched to the mechanical coolant pump, and the coolant pump is not
covered. In this case, the coolant is pumped through the coolant pump impeller.

The charge pressure control for the EA825 V8 TFSI turbochargers is electropneumatic.

This means that charge pressure positioners V465 and V546 are electropneumatic pressure converters. Depending
on activation (PWM) by the engine control unit, they are able to induce a calculated negative pressure
(characteristic curve). This determines the opening path of the wastegate. They are open when they are not
activated.

SSP 676 contains more information on the EA825 V8 TFSI engine cooling system.

Production Solution
Not applicable.

Service

If the coolant temperature in the vehicle is too high:
Remove the vacuum hose on the mechanical coolant pump (number 13 in Figure 1).
Check whether this results in lower engine coolant temperatures.

If the coolant temperature drops, replace the electric changeover valve for the switchable mechanical coolant pump
N649 according to the Workshop Manual.

Also check whether there are traces of coolant in the vacuum hose between the mechanical coolant pump and
N649, or in the vacuum connection of N649. If there are traces of coolant, please also replace the switchable
mechanical coolant pump and the vacuum hose between the mechanical coolant pump and N649 according to the
Workshop Manual and provide images.

If the coolant temperature in the vehicle is not too high, but the exhaust emissions warning lamp is on and
event memory entry P0299 (Turbo/Super Charger Underboost) is logged:

Check the vacuum system for leaks. If a leak is detected on N649, replace N649 according to the Workshop
Manual.

Also check whether there are traces of coolant in the vacuum hose between the mechanical coolant pump N649, or
in the vacuum connection of N649. If there are traces of coolant, please also replace the switchable mechanical
coolant pump and the vacuum hose between the mechanical coolant pump and N649 according to the Workshop
Manual and provide images.

When billing, please always attach photo(s) or video(s) that clearly shows the complaint to DOC-IT. To ensure a
reference to the vehicle, the image(s) or video(s) must:

* — Include the VIN and date.
+ Must not be edited.
* Should be in focus and taken with sufficient light. A high resolution is not necessary.

If appropriate, please mark the location of the problem so that parts analysis has a clear reference to the complaint.
Please ensue that the photo documentation does not show any persons and/or face, license plates, or customer
data.

21 20 19 18

Figure 1. Assembly overview — coolant pump/thermostat incl. switchable mechanical coolant pump, number 12.

r

1112 13 14 15

29 28 27
Figure 2. Assembly overview — vacuum system incl. N649, number 9.
Warranty
Claim Type: + Ifthe vehicle is outside of any warranty, this Technical Service Bulletin is

informational only.

Service Number:

Case 1: Both N649 and the coolant pump have been replaced due to traces of coolant in
the vacuum line or in N649. Use service number: 1950

Case 2: Only N649 replaced due to no traces of coolant in the vacuum line or in N649.
Use service number 1985.

Damage Code: Case 1: 050
Case 2: 010
Labor Operations: Remove and install valve N649 1984 19xx See SRT with

associated
operations