2018-2021 Audi 48V System Warning DTC P0CA700 U046900

Owners of 2018-2021 Audi models may experience an Audi 48V system warning in the instrument cluster. This warning can be intermittent and may be accompanied by other significant issues. This Technical Service Bulletin (TSB) 2058831/4, issued on March 2, 2022, addresses these concerns. It supersedes a previous bulletin, Group 27 number 21-40, dated December 6, 2021.

Revision History

This bulletin has undergone several revisions to refine its guidance:

• Revision 4: Updated the labor operation details within the warranty section.
• Revision 3 (December 6, 2021): Revised the condition description to include additional customer statements, expanded the technical background information, updated the service procedure with a new photo and steps 1-2, and revised the warranty labor operation.
• Revision 2 (April 1, 2021): Updated the header to include Model Year 2021 vehicles.

Symptoms

Owners might notice an intermittent "Intermittently a warning for the 48V vehicle electrical system is displayed in the instrument cluster." Additionally, customers may report one or more of the following conditions:

• "The vehicle does not start."
• "The vehicle stalled."
• "The battery is dead."

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:

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

Technical Background

The root cause of the Audi 48V system warning and related issues is often a software discrepancy in the starter/generator control module, C29 (address word 00CC). If the 48V vehicle electrical system warning displayed in the instrument cluster is ignored, the 12V system may drain. This can lead to critical vehicle conditions such as a vehicle stall or a no-start situation.

Diagnosis / Trigger Conditions

For vehicles presenting with DTC U046900 in the Engine Control Module (ECM), J623, technicians should check the expanded ambient conditions of this DTC. Specifically, they need to look for the value of "Starter generator, actual mode 48V".

Figure 1 in the bulletin illustrates a DTC U046900 entry with an expanded ambient condition showing the "Starter generator, actual mode 48V" value as '5' in the ECM, J623. If this value is '5', the starter/generator should be replaced. If no value is displayed, an ODIS feedback should be submitted.

Repair Procedure Summary

The primary solution involves updating the software of the starter/generator control module, C29. This procedure requires following the instructions outlined in TSB 2011732: 00 Software Version Management (SVM), operating instructions.

Technicians will update the starter/generator control module, C29 (address word 00CC), using the SVM action code listed below:

Model	Old Hardware Part Number	Old Hardware Version	Old Software Part Number	Old Software Version	New Software Version	SVM Code Input
A6, A7, Q7, Q8	4N0903028	H17	4N0903028	523	527	CCA001

If the diagnostic step for DTC U046900 indicates a "Starter generator, actual mode 48V" value of 5, the starter-alternator must be replaced instead of just a software update.

Warranty Information

Repairs for this issue are covered under specific warranty conditions:

• Claim Type 110: For vehicles up to 48 months or 50,000 miles.
• Claim Type G10: For Audi Certified Pre-Owned (CPO) vehicles, requiring owner verification.

Important Warning: If your vehicle falls outside of these warranty periods, this Technical Service Bulletin is for informational purposes only, meaning the repair cost may not be covered.

The service number for this bulletin is 2726, with a damage code of 0040. Labor operations include:

• Software Update (Includes checking for DTCs): Operation code 0151 0000, with time stated on the diagnostic protocol (maximum 100 Time Units). This is only performed if an update is required.
• Replace starter-alternator: Operation code 2726 XXXX, applicable only if the expanded ambient condition "Starter generator, actual mode 48V" value is 5. Refer to the Service Repair Time (SRT) for associated operations.
• Diagnostic Time (GFF): Operation code 0150 0000, only if a part is replaced, with time stated on the diagnostic protocol (maximum 100 Time Units).

Road tests performed prior to the service procedure are not covered and have no allowance (0 TU).

Additional Information

To complete this procedure, technicians will also need to refer to TSB 2011732: 00 Software Version Management (SVM), operating instructions. All part and service references provided in this TSB 2058831/4 are subject to change. Always consult your Parts Department and/or ETKA for the latest information and parts bulletins. The Repair Manual should also be checked for any fasteners, bolts, nuts, and screws that require replacement during the repair.

NHTSA ID: 10208897