2021-2023 Audi 48V Electrical System Warning DTC P0CA700

Owners of certain 2021-2023 Audi models may experience an "Electrical system: fault" message or a battery warning light appearing on their instrument cluster. This issue is addressed by Audi Technical Service Bulletin (TSB) 27 23 55 2058831/8, which provides diagnostic and repair procedures for related Diagnostic Trouble Codes (DTCs) P0CA700 and U046900.

This TSB, revision 8, dated May 8, 2023, supersedes an earlier bulletin, Group 27 number 23-51 dated March 30, 2023. It applies to 2021-2023 Audi A6, A7, Q7, Q8, A6 allroad, and S8 vehicles equipped with the 48V Mild Hybrid Electric Vehicle (MHEV) system.

Symptoms

Owners might notice the following indications of a problem with their Audi's 48V electrical system:

• The instrument cluster displays the message: "Electrical system: fault. See owner's manual”.
• A yellow or red battery warning symbol appears on the instrument cluster.

These symptoms suggest an underlying issue with the vehicle's 48V electrical system, specifically involving the Belt Starter Generator (BSG) or related control modules.

Fault Codes / DTCs

Workshop findings indicate that one or more of the following Diagnostic Trouble Codes (DTCs) may be stored in the vehicle's control modules:

• DTC P0CA700: Stored in the Battery management 2 (Battery 48V) control module, J1120 (address word 0021). This code indicates "Hybrid battery discharge current too high."
• DTC U046900: Stored in the ECM, J623 (address word 0001), or the Gateway, J533 (address word 0019). This code signifies "Invalid data received from starter/generator control module (Symptom 36564)."

Diagnosis

The TSB outlines a diagnostic process to determine the root cause of the Audi Q8 electrical system warning. The Belt Starter Generator (BSG) and the vehicle's 48V system work together to provide electrical power. Traditional diagnostic methods are not always applicable due to the intelligent regulation of the BSG's output.

Technicians will check for extended ambient conditions when DTC U046900 is stored. If the BSG's software is older than SW 0527, an update is required. After the software update or if the software is already current, further diagnostic steps involve checking specific measurement values in the 00CC - Starter Generator module using ODIS, such as [IDE12494]_Voltages, [IDE12495]_Torques, and [VO]_operation_mode.

These values help determine if the BSG is functioning correctly. For example, if the Starter generator, actual mode 48V value is not shown or is not '5', or if the software is older than SW 0527, a software update is necessary. If the BSG is working within specifications, further diagnostics outside the scope of this TSB may be needed to resolve the Audi Q8 electrical system warning.

Repair Procedure Summary

The repair procedure for the Audi Q8 electrical system warning primarily involves a software update for the starter/generator control module, C23 (address word 00CC), if the existing software is outdated. This update is performed using the SVM update instructions detailed in TSB 2011732: 00 Software Version management (SVM), operating instructions.

If the software update does not resolve the issue, or if the BSG software is already current, technicians will proceed with detailed measurement value checks. These checks involve monitoring specified torque values and voltage levels to assess the BSG's performance. Depending on these measurements, the BSG may need to be replaced if it's not charging correctly or if an inverter fault is detected.

Required Software and Parts

To address the Audi Q8 electrical system warning and related DTCs, the following may be required:

• Software Update: For the starter/generator control module, C23 (address word 00CC). The new software version is 527, superseding older versions like 523.
• SVM Code Input: CCA001 is used for the software update.
• Hardware Part Number: 4N0903028 (Old and New) for the starter/generator control module.
• Hardware Versions: Old hardware version H17, with new versions including F, G, H, J, M, and N.

Important Warnings

Owners should be aware of specific diagnostic steps that technicians may perform:

If both torque values are 0, attempt to force the vehicle into providing electrical power from the BSG by turning the steering wheel several times to both end stops and back. You can also activate auxiliary system, like the HVAC blower to high, rear window heating, seat heaters to increase the electrical load on the vehicle.

This procedure helps determine if the Belt Starter Generator is capable of producing electrical power under load.

Owner Action

If your 2021-2023 Audi A6, A7, Q7, Q8, A6 allroad, or S8 displays an "Electrical system: fault" message or a battery warning symbol, it is recommended to schedule a service appointment with an authorized Audi dealership. The dealership will be able to diagnose the issue, check for DTCs P0CA700 and U046900, and apply the necessary software updates or perform hardware replacements as outlined in TSB 27 23 55 2058831/8. Warranty claims for this service are typically covered for up to 48 months/50,000 miles, or under specific Certified Pre-Owned (CPO) and Starter-Alternator Limited Warranty Extensions.

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Source: NHTSA ID: 10236583