2018-2023 Audi Electrical System Warning P0CA700 U046900 TSB

Owners of certain 2018-2023 Audi vehicles may encounter an Audi 48V electrical system warning message on their instrument cluster. This warning, often displayed as "Electrical system: fault. See owner's manual," can be accompanied by a yellow or red battery warning symbol. Audi Technical Service Bulletin (TSB) 2058831/7 addresses these concerns, providing diagnostic and repair procedures for issues related to the 48V electrical system and the Belt Starter Generator (BSG).

This TSB, dated March 30, 2023, supersedes previous bulletin Group 27 number 23-49 from March 23, 2023, and has undergone several revisions to refine its guidance on diagnosis and repair.

Symptoms

If your Audi is affected by this issue, you may observe the following:

• An instrument cluster message stating: "Electrical system: fault. See owner's manual".
• A yellow or red battery warning symbol illuminated on the instrument cluster.

Fault Codes / DTCs

Technicians diagnosing the Audi 48V electrical system warning may find one or both of the following Diagnostic Trouble Codes (DTCs) stored in the vehicle's control modules:

Code	Description	Module
P0CA700	Hybrid battery discharge current too high	Battery management 2 (Battery 48V) control module, J1120 (address 0021)
U046900	Invalid data received from starter/generator control module	ECM, J623 (address 0001), or Gateway, J533 (address 0019)

Diagnosis and Trigger Conditions

The 48V Belt Starter Generator (BSG) system is an intelligent component that supplies electrical power to the vehicle. Unlike traditional alternators, its output is regulated based on the vehicle's current needs, making conventional diagnostic methods less effective. For more detailed information on the 48V system, technicians are referred to TSB 2067906.

Diagnosis involves checking the BSG's software version and specific measurement values. If the "Starter generator, actual mode 48V" value is not displayed or is not '5', and the software version is older than SW 0527, a software update is required. If the software is up to date or the value is '5', further diagnostic steps are necessary to determine if the BSG is the root cause of the Audi 48V electrical system warning.

Diagnostic steps include:

1. Accessing measurement values for the starter generator via ODIS, specifically [IDE12494]_Voltages, [IDE12495]_Torques, and [VO]_operation_mode.
2. Checking the voltage of terminal 87 (should be between 11.6V and 15V) and terminal 40 (should be between 40V and 50V).
3. Comparing the "Specified torque" and "Starter-alternator torque" values. These should be similar (within 5 Nm).

Repair Procedure Summary

The primary repair involves updating the software of the starter/generator control module (C23, address word 00CC). This is done using the Software Version Management (SVM) system, following instructions in TSB 2011732. The required SVM action code for this update is CCA001.

For vehicles with old hardware part number 4N0903028 (versions H, J, M, N) and old software version 523, the new software version 527 should be installed. If the software update does not resolve the issue, or if diagnostic tests indicate a hardware fault, the Belt Starter Generator may need replacement.

Important Warnings

Owners and technicians should be aware of specific conditions under which parts should not be replaced:

• If both the specified torque and starter-alternator torque values are 0, and the operation mode is "Standby," there is "No charging demand = do not replace belt-driven starter-alternator." In this scenario, the vehicle's electrical load should be increased (e.g., by turning the steering wheel, activating HVAC, rear window heating, or seat heaters) to force the BSG to provide power.
• If the specified torque is -9.5 Nm and the starter-alternator torque is also -9.5 Nm, with the operation mode as "TorqueControlled," this indicates "Belt-driven starter-alternator charging = do not replace belt-driven starter-alternator."

Replacing the BSG unnecessarily will not resolve the underlying issue if the problem is related to software or a lack of charging demand.

Warranty Information

Warranty claims for this issue can be submitted under various claim types, including:

• 110: For vehicles up to 48 months or 50,000 miles.
• G10: For CPO (Certified Pre-Owned) vehicles, requiring owner verification.
• 1-GW: For vehicles covered by the Starter-Alternator Limited Warranty Extension.

The service number is 2726. Damage codes are 0039 for software updates only (no part replacement) and 0040 if the starter-alternator is replaced. Labor operations include 0151 0000 for software updates and 2726 0199 for checking the starter-alternator. Diagnostic time is 0150 0000 for GFF (Guided Fault Finding) if no software update was performed.

All warranty claims must adhere to the Audi Warranty Policies and Procedures Manual and are subject to review.

Additional Resources

For comprehensive information, technicians should also consult:

• TSB 2011732: 00 Software Version Management (SVM), operating instructions.
• TSB 2067906: 27 48V Reference: diagnosis and system information.

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Source: NHTSA ID 10233488