Technical Service Bulletin
Topic

Turbo Charger Under-boost - DTC P029900 is evident in 0001 | V8 Kovomo | All
Models

Market area

Bentley: worldwide (2WBE),China 796 VW Import Comp. Ltd (Vico), Beijing (6796)

Brand

Bentley

Transaction No. 2079115/1
Level

EH

Status

Released for publishing

Release date

Jan 27, 2026

Diagnostic trouble codes

Diagnostic address

Diagnostic trouble code

Fault symptom Storage state

0001 - Engine electronics P029900: Turbo/Super Charger Underboost

static

0001 - Engine electronics P029900: Turbo/Super Charger Underboost

Intermittent

New customer code

Object of complaint

Complaint type Position

engine -> intake system, compressor systems, vacuum system leaks

Vehicle data
V8 Kovomo Variants
Sales types

Type MY

Brand Designation Engine code Gearbox code Final drive code

3S3* 2018 E

*

*

*

3S3* 2019 E

*

*

*

3S3* 2020 E

*

*

*

3S3* 2021 E

*

*

*

3S3* 2022 E

*

*

*

3S3* 2023 E

*

*

*

3S3* 2024 E

*

*

*

3S4* 2019 E

*

*

*

3S4* 2020 E

*

*

*

3S4* 2021 E

*

*

*

3S4* 2022 E

*

*

*

3S4* 2023 E

*

*

*

3S4* 2024 E

*

*

*

4V1* 2018 E

*

*

*

4V1* 2019 E

*

*

*

4V1* 2020 E

*

*

*

4V1* 2021 E

*

*

*

4V1* 2022 E

*

*

*

4V1* 2023 E

*

*

*

4V1* 2024 E

*

*

*

4V1* 2025 E

*

*

*

4V1* 2026 E

*

*

*

Z23* 2025 E

*

*

*

Z23* 2026 E

*

*

*

Z24* 2025 E

*

*

*

Z24* 2026 E

*

*

*

Z32* 2025 E

*

*

*

Z32* 2026 E

*

*

*

ZG2* 2020 E

*

*

*

ZG2* 2021 E

*

*

*

ZG2* 2022 E

*

*

*

ZG2* 2023 E

*

*

*

ZG2* 2024 E

*

*

*

ZV1* 2023 E

*

*

*

ZV1* 2024 E

*

*

*

ZV1* 2025 E

*

*

*

Documents
Document name
master.xml

Technical Service Bulletin
Turbo Charger Under-boost - DTC P029900 is evident in 0001 | V8 Kovomo | All
Models

Transaction No.: 2079115

/1
Release date: Jan 27,
2026

Condition
Customer Statement:
The engine warning light comes on and the vehicle loses power.
Workshop Findings:
Customer statement can be verified and the following entries may be logged within the engine control unit.
•

P029900: Turbo/Super Charger Under-boost, passive/sporadic.

Technical Background
The wastegate actuator relies on vacuum pressure to regulate turbocharger boost. If vacuum is not
maintained, the wastegate may remain open, preventing the turbocharger from generating full boost. This
can trigger engine protection mode, limiting performance and displaying warnings in the DIP. Refer to the
measure section for guided fault-finding steps.

Production Solution
Not Applicable

Service
Vacuum System Layout – Use for Illustration purposes only

A) Switch valve for
mechanical coolant
pump

B) Coolant Pump

C) Vacuum pump

D) Connection for
vacuum reservoir

E) Boost pressure
control solenoid 1

F) Outlet (Vacuum
pressure input)

G) Connection for
Vacuum unit/turbo
charger

H) Boost pressure control
solenoid 2

Step 1 – Wastegate Vacuum Test
Connect a vacuum hand pump with gauge directly to the wastegate actuator.
•

Apply vacuum and monitor whether the actuator maintains pressure steadily.

•

If vacuum drops: Suspect a leak in the actuator, replace actuator.

NOTICE
Provide video evidence via a full technical DISS query that the actuator does not hold vacuum prior to part
replacement.

Step 2 – Boost Pressure Control Solenoid Check
Locate the boost pressure control solenoids.
Inspect the electrical connectors for:
•

Corrosion

•

Loose pins

•

Incorrect positioning

Activate the solenoid using ODIS and listen for the activation click:
•

If click is heard: Proceed to Step 3.

NOTICE
If no clear audible click is detected, record audio or video evidence for DISS and warranty submission,
then proceed to Step 3.

Step 3 – Inspect the entire vacuum line system for coolant and/or oil contamination and potential blockages
•

If no oil contamination and/or coolant is found continue to step 4.

•

If oil contamination is found replace the vacuum pump and relevant vacuum system lines and
solenoids.

NOTICE
If oil confirmation is present, record photographic evidence for DISS and warranty submission prior to part
replacement.

Step 4 – Coolant Pump Vacuum Integrity Check
Verify the coolant pump holds vacuum using a vacuum gauge:
•

Pull vacuum directly from the pump for a minimum of 5 minutes.

•

If it does not hold vacuum, replace the coolant pump and solenoid.

If coolant is present:
Replace the affected vacuum lines and the relevant vacuum solenoids.

NOTICE
Provide video evidence via DISS that it the coolant pump does not hold vacuum prior to part replacement

Step 5 – System Reassembly and Road Test
•

Reassemble all components.

•

Clear Diagnostic Trouble Codes (DTCs) using ODIS.

•

Conduct a road test under load conditions.

•

Monitor boost pressure during the test.

•

Check for any recurrence of fault codes or warning messages on the Driver Information Panel.

•

If the fault reoccurs, include evidence of all checks completed on new or existing DISS query.

•

Confirm that full boost is achieved and engine performance is fully restored.

Warranty
Warranty type - 110 or 910
Damage service number - 21 65
Damage code - 00 55
Diagnosis Time
Labour operation code - 21 65 01 95 (Live on 26.02.2026, use 21 65 01 99 prior to this date)
Time Must not exceed - 120 TU
Road Test
Labour operation code - 01 21 00 01
Time - 30 TU

If any parts need to be replaced, refer to the warranty accounting instructions in ElsaPro. This is required
due to the wide range of vehicle specifications and symptom scenarios.

NOTICE
All claims will be checked by the Warranty team, any claims which are not deemed as applicable will be
cancelled. In the event that parts are replaced parts without the required attachments or the parts are
found to be not at fault warranty claims will be liable for rejection

Required Parts and Tools
Refer to ETKA parts catalogue