Electrical diagnosis / OEM retrofit

A6 Allroad Electronics

My A6 Allroad’s LTE connection went offline. After trying every reset I could find, I took apart most of the trunk interior to reach the SOS module’s backup battery. Since the trunk was already open, I used the same teardown to retrofit the OEM tire-pressure monitoring system, including routing its harness beneath the rear seat. Disconnecting the backup battery changed nothing; the LTE connection returned by itself a few days later.

Trunk interior removed / electronics exposed

01 / LTE diagnosis

Trying every reset.

The first attempts were software resets and an engineering reboot. When none of them restored the data connection, I worked through the fuse panels and eventually removed the trunk trim to reach the telematics hardware and its backup battery.

Audi engineering reboot screen on the upper MMI display — Engineering reboot

Fuse panels beneath the A6 Allroad cargo floor — Fuse access under the cargo floor

Side trim removed from the A6 Allroad trunk to expose wiring and modules — Left-side trunk trim removed

SOS module backup battery exposed on a work desk — SOS module backup battery

Outcome

Disconnecting the backup battery did not bring the LTE connection back. A few days later, the system returned online on its own.

02 / OEM TPMS retrofit

Adding the factory system.

With the trunk already apart for the LTE diagnosis, I used the same access to fit the OEM receiver and connect its harness to the existing electrical system. The wiring route continued beneath the rear seat, so that came out too.

OEM Audi tire-pressure monitoring receiver with its wiring harness — OEM TPMS receiver and harness

A6 Allroad electrical modules and wiring exposed beneath the cargo floor — Factory wiring and control modules

A6 Allroad cargo area stripped for wiring access — The same open cargo area, now used for TPMS wiring

Rear seat removed from the Audi A6 Allroad during the TPMS retrofit — Rear seat removed for the harness route