Service

Technical Information

79/25

ENU

2703

2

Warning Message “Vehicle Electrical System Faulty” and Active Malfunction Indicator Light in the
Instrument Cluster / Fault Memory Entries in the High-Voltage Voltage Converter Control Unit (79/25)
Vehicle Type:

911 GTS (992)/911 4 GTS (992)

Model Year:

2025

Concerns:

HV voltage converter

Information:

The customer complains about the yellow or red warning message “Vehicle electrical system faulty”
lighting up as well as an active malfunction indicator light.
In rare cases, it is no longer possible to start the vehicle.
One of the following fault memory entries is stored in the high-voltage voltage converter control unit fault
memory:
•
•

P0A9400 - Voltage converter, missing power (0A189B)
P0C3900 - High-voltage voltage converter, temperature sensor 1, implausible signal (0A1858)

In connection with the fault memory entry “P0C3900”, the yellow battery warning message “Battery low”
can also light up in the instrument cluster.
After an ignition change or bus idle, the complaint is no longer active for the time being.
Information
Replacing the high-voltage voltage converter is not expedient for the aforementioned complaint.
Action:

In the event of an existing customer complaint, re-program the high-voltage voltage converter control
unit using the PIWIS Tester.
Information
The minimum programming requirement is the PIWIS Tester software release 43.800.026 (or higher)

Required tools
Tools:

•
•

P90999 - PIWIS Tester 4
Battery charger with a current rating of at least 90 A and a current and voltage-controlled charge map
for lithium starter batteries, e.g., VAS 5908 - battery charger 90 A. For further information about the
battery chargers to be used, see the corresponding Workshop Manual. ⇒ Workshop Manual '270689
Charge battery and vehicle electrical system'

Re-program the high-voltage voltage converter control unit.
Work Procedure: 1

Re-program the high-voltage voltage converter control unit.

AfterSales

Jan 29, 2026
Page 1 of 3

2

Service
2703

ENU

Technical Information

79/25

The basic procedure for control unit programming is described in the Workshop Manual.
⇒ Workshop Manual '9X00IN Basic instructions and procedure for control unit programming using the
PIWIS Tester'
Specific information on control unit programming during this action:
Required PIWIS Tester software release:

43.800.026 (or higher)

Type of control unit programming:

Control unit programming using the 'A utomatic
programming' function of the control unit:
“High-voltage voltage converter” control unit
– “Coding / Programming” menu – “Automatic
programming” function.

Programming sequence:

Read and follow the information and instructions
of the PIWIS Tester during the guided
programming sequence.
During the programming sequence, the control
unit is re-programmed and then automatically
re-coded.
Do not interrupt the programming and coding
process.
Backup documentation for the re-programmed
software releases starts after programming.

Programming duration:

Programming takes up to 2 minutes, depending on
equipment.

Software programmed during this action:

• High-voltage voltage converter control unit
Software release: 0010 (or higher)
Following control unit programming, the software
release can be read out using the PIWIS Tester in
the menu ⇒ ‘Extended identifications’.

Jan 29, 2026
Page 2 of 3

Procedure in the event of error messages
appearing during the programming sequence:

⇒ Workshop Manual '9X00IN Basic instructions
and procedure for control unit programming using
the PIWIS Tester'

Procedure in the event of a cancellation of the
control unit programming:

Repeat control unit programming by restarting
programming.

2

Read out and delete all control unit fault memories.

3

Exit the diagnostic application, switch off the ignition and disconnect P90999 - PIWIS Tester 4 from
the vehicle.

AfterSales

Service

Technical Information
4

79/25

ENU

2703

2

Switch off and disconnect the battery charger.

⇒ Workshop Manual '270689 Charging vehicle electrical system battery'

Labor position and PCSS encryption
Labor position:
APOS

Labor operation

I No.

27032550

Programming the voltage transformer
PCSS encryption:

Location (FES5)

27030

Voltage converter

Damage type (SA4)

1134

Programming error

Important Notice: Technical Bulletins issued by Porsche Cars North America, Inc. are intended only for use by professional automotive technicians who have attended Porsche service training courses. They are
written to inform those technicians of conditions that may occur on some Porsche vehicles, or to provide information that could assist in the proper servicing of a vehicle. Porsche special tools may be necessary in
order to perform certain operations identified in these bulletins. Use of tools and procedures other than those Porsche recommends in these bulletins may be detrimental to the safe operation of your vehicle, and
may endanger the people working on it. Properly trained Porsche technicians have the equipment, tools, safety instructions, and know-how to do the job properly and safely. Part numbers listed in these bulletins
are for reference only. The work procedures updated electronically in the Porsche PIWIS diagnostic and testing device take precedence and, in the event of a discrepancy, the work procedures in the PIWIS Tester
are the ones that must be followed.

© 2026 Porsche Cars North America, Inc.

AfterSales

Jan 29, 2026
Page 3 of 3