2021-2022 Audi A4/A5 Check Engine Light DTC U064000 U064100

Symptoms

Owners of affected 2021-2022 Audi A4 and A5 vehicles may notice that the "The check engine warning lamp comes on." This indicates a potential issue with the vehicle's emission control system.

Fault Codes / DTCs

When the check engine light illuminates, diagnostic trouble codes (DTCs) related to the fuel tank breather system may be stored sporadically in the Engine Control Module (J623). These are the specific codes associated with this issue:

Code	Description
U064000	Lost Communication with EVAP Fuel Vapor Temperature Sensor Circuit
U064100	Lost Communication with EVAP System Pressure Sensor/Switch Circuit "A"

Important Warnings

Audi has identified a specific diagnostic pitfall for this issue. Owners and technicians should be aware that replacing the tank pressure sender will not fix the problem. The root cause lies elsewhere, as detailed in this bulletin.

Technical Background

The underlying cause for the "Audi A4 A5 check engine light" and associated DTCs U064000 and U064100 is electromagnetic interference (EMI). This interference can negatively affect the signal from the fuel tank breather system, leading to the communication errors and the illumination of the check engine warning lamp.

Repair Procedure Summary

For sporadically stored DTCs U064000 or U064100, the repair involves modifying the wiring harness. This procedure, outlined in Technical Service Bulletin 2069123/1, includes several steps:

1. Accessing the Wiring Harness: Technicians will begin by removing the plenum chamber covers and releasing the wiring harness securing clips to expose the relevant wiring.
2. Wire Isolation and Preparation: Specific yellow/grey and yellow/purple wires within the left and right bundles will be isolated. These wires are then cut and carefully unraveled.
3. Harness Modification: Using a wire harness repair set, the untwisted yellow/grey wire (from the plenum chamber side) is connected to the yellow/purple wire (engine side) in the right bundle. Concurrently, the remaining yellow/purple wire (plenum side) is connected to the yellow/grey wire (engine side).
4. Final Steps: After the wiring modification, diagnostic trouble codes are cleared, and the system functionality is rechecked. The modified wiring harness is then wrapped in adhesive tape N 10729002, and the vehicle is reassembled.

Required Tools and Parts

To perform this repair, specific tools and parts are necessary:

• Wire harness repair set VAS 1978 B
• Butt connector, part number 000979940 (Quantity: 2)
• Adhesive tape, part number N 10729002 (Quantity: 2)
• Fasteners, bolts, nuts, and screws as needed, referenced in ETKA and the Repair Manual.

Warranty Information

This repair is covered under warranty for up to 48 months or 50,000 miles, whichever comes first. For Audi Certified Pre-Owned (CPO) vehicles, coverage is provided under claim type G10, requiring verification of ownership. If the vehicle is outside of these warranty parameters, Technical Service Bulletin 2069123/1 serves as informational guidance only.

The service number associated with this procedure is 9709, and the damage code is 0040. Labor operations include removing and installing plenum chamber covers (8522 1900), repairing the wiring harness (9709 4152), modifying the wiring harness (9709 4999), and diagnostic time (0150 0000), along with road tests (0121 0004).

Source: NHTSA ID 10230847