2021-2025 Audi PHEV Exhaust Emissions Warning Lamp TSB

Symptoms of the Audi PHEV MIL Warning

Owners of certain 2021-2025 Audi A7, A8, and Q5 PHEV models may observe the "Exhaust emissions warning lamp (MIL) active" on their instrument cluster. This warning indicates a potential issue within the emissions control system. Additionally, the vehicle's malfunction display might show general "emissions control system malfunction display" symbols.

It is important to note that this specific issue, as described in Audi Technical Service Bulletin (TSB) 2079117/1, typically occurs without any actual problems with the vehicle's air conditioning (A/C) system. The primary symptom is solely the illumination of the MIL, which can be a concerning "Audi PHEV MIL warning" for drivers.

Fault Codes (DTCs) and Diagnostic Address

When the "Exhaust emissions warning lamp (MIL) active" condition occurs, a technician performing a diagnostic scan will likely find one or more of the following event memory entries logged in the thermal management control unit, specifically at diagnostic address 00C5. These codes point to implausible signals from the refrigerant pressure sensors, even if the sensors are functioning correctly.

Code	Description	Symptom (HEX)	Symptom (DEC)
P053100	A/C Pressure/Temperature Sensor 1, implausible signal	0x00D6D8	55000
P0EBF00	A/C Pressure/Temperature Sensor 1, implausible signal	0x00D6DE	55006
P0EBF00	A/C Pressure/Temperature Sensor 1, implausible signal	0x00D6ED	55021
P251600	A/C Pressure/Temperature Sensor 2, implausible signal	0x00D6D9	55001
P0EC400	A/C Pressure/Temperature Sensor 2, implausible signal	0x00D6DF	55007
P0EC400	A/C Pressure/Temperature Sensor 2, implausible signal	0x00D6EE	55022
P1C5E00	A/C Pressure/Temperature Sensor 3, implausible signal	0x00D6DA	55002
P1C5E00	A/C Pressure/Temperature Sensor 3, implausible signal	0x00D6E0	55008
P1C5E00	A/C Pressure/Temperature Sensor 3, implausible signal	0x00D6EF	55023

These codes specifically relate to refrigerant pressure senders PT1, PT2, and PT3, indicating that the thermal management control unit is receiving unexpected data from these components, triggering the "Audi PHEV MIL warning."

Technical Background and Diagnosis

Audi has identified the root cause of this particular "Audi PHEV MIL warning" as a software issue. This means that the vehicle's control unit may incorrectly interpret signals from the refrigerant pressure sensors, leading to the logging of fault codes and the activation of the MIL, even when the sensors themselves are functioning correctly and there is no actual fault with the A/C system or emissions.

For diagnosis, technicians are instructed to first reproduce the complaint and then check the event memory entries in the thermal management control unit (diagnostic address 00C5). A crucial step involves verifying the part index of the installed refrigerant pressure sensors. Specifically, if refrigerant pressure sensors with part number 4M0959603J are installed on the affected vehicle, these event memory entries may be logged without a genuine underlying issue.

Repair Procedure Summary

The repair procedure outlined in TSB 2079117/1 is primarily diagnostic and informational. The key steps for technicians are:

1. Verify Event Memory Entries: Confirm that one or more of the specified DTCs (P053100, P0EBF00, P251600, P0EC400, P1C5E00) are logged in the thermal management control unit (00C5).
2. Check Refrigerant Pressure Sensor Part Index: Determine if the refrigerant pressure sensors installed in the vehicle have part number 4M0959603J.
3. Action Based on Part Index: If the part index of the refrigerant pressure sensors is 'J' (indicating part number 4M0959603J), the event memory entries can be ignored and deleted. This action resolves the "Audi PHEV MIL warning" by clearing the erroneously logged codes.

This procedure highlights that for vehicles with the specific sensor part, the fault codes are often a misinterpretation by the software rather than a hardware failure, and replacement of the sensor is typically not required.

Important Warnings for Owners and Technicians

This Technical Service Bulletin includes critical guidance regarding the diagnosis and resolution of the "Exhaust emissions warning lamp (MIL) active" condition:

• "If the index is J, the event memory entries can be ignored and deleted."
• "However, if the same event memory entry as described above in 'Workshop findings' is logged in the vehicle but with a different symptom and there is also an issue with air conditioning system, the entries cannot be ignored."

This means that if your vehicle exhibits the MIL warning and logs these specific DTCs, but also has a noticeable problem with the A/C system or other symptoms beyond just the light, a more thorough investigation is required. The instruction to ignore and delete applies only when the MIL is active solely due to these codes and without any other functional issues. This distinction is crucial for proper diagnosis and to avoid unnecessary repairs for the Audi PHEV MIL warning.

Warranty Information

For vehicles still under warranty, repairs related to this TSB will typically be covered. The Service Number associated with this issue is 8711, and the Damage Code is 0040. Labor operations for addressing this concern involve Guided Functions (GFF), with operation codes 0150 0010 and 0150 0060. These operations are performed according to the diagnostic log and reference TSB 2079117/1.

If your Audi PHEV is outside of its warranty period, this Technical Service Bulletin serves as informational guidance. Owners should consult with their Audi dealership for specific details regarding potential costs if the vehicle is no longer covered, as the TSB states it is informational only in such cases.

Owner Action

If you are experiencing the "Audi PHEV MIL warning" or the "Exhaust emissions warning lamp (MIL) active" in your 2021-2025 Audi A7, A8, or Q5 PHEV, and no other A/C system issues are present, it is recommended to schedule an appointment with an authorized Audi service center. Inform them about the persistent MIL warning and mention Audi Technical Service Bulletin 2079117/1. The technicians will be able to perform the necessary diagnostic checks, including verifying the refrigerant pressure sensor part index, and apply the appropriate resolution as outlined in the TSB.

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Source: NHTSA ID: 11022714