2018 Audi A4 Powertrain & Transmission Problems

A vehicle diagnostic scan dated 04/15/2026 at approximately 88,502 miles showed a stored transmission electronics fault: P084100, described as “Transmission fluid pressure sensor/switch A range/performance,” with status listed as passive/sporadic. This indicates a transmission / powertrain control concern involving the transmission fluid pressure sensor, transmission electronics, wiring, control logic, pressure monitoring, or related powertrain components. The vehicle also has prior transmission/powertrain history, including a March 2023 transmission-pan-gasket concern documented in service records, so this later transmission electronics fault is being reported in that broader powertrain context. This is being reported as a safety concern because a transmission fluid pressure sensor or transmission-control fault can affect shifting, drivability, delayed engagement, slipping, harsh shifting, limp mode, reduced power, drivetrain damage, or loss of propulsion while driving. Even if the fault is intermittent, a transmission-control issue may create an unsafe condition if it occurs in traffic or during acceleration, merging, turning, or normal driving. No crash, fire, injury, or fatality occurred. The vehicle/component is available for inspection, and the diagnostic scan report, transmission-related records, service records, manufacturer communications, and related communications are available if requested.

See attached document for complaint

While driving there was an internal failure of the front differential which caused debris to fly out and the debris then punctured the transmission according to the diagnosis on an Audi dealership. The car jerked to a stop and would not move. If this happens at high speed it represents a sever safety risk to the occupants. The vehicle has been inspected by the manufacturer and insurance representatives as well as by a dealer. There were no warning lamps, messages or other symptoms and this happened with no warning.

The all-wheel-drive clutch in the vehicle had to be replaced. The symptoms were heavy vibrations or thumping when starting to drive forward from a stop with the wheels turned in either direction. A dealership - New Country Audi of Greenwich - did the repair at a cost of $4,308.85 (including tax). This drivetrain failure occurred at less than 48,000 miles. The vehicle came with a 50,000 mile or 4 year warranty. Since it was in service for over 5 years, this defect was not covered under warranty. There is a Techical Service Bulletin on this issue, number 39 21 43 2059057/4 July 16, 2021. The dealer confirmed my issue was indeed the same as that addressed in the TSB. It seems to me that a major known issue occurring at less than 50,000 miles is a defect. I do not know if it is ultimately a safety hazard, but it seems it could become dangerous if not addressed. For reference, I am attaching the TSB and the repair invoice.

ENGINE MALFUNCTION PREVENTED THE VEHICLE TO ENGAGE AND A SIGNIFICANT LAG. CORRECTION OF THE FAILURE HAS BEEN ATTEMPTED TWICE AND A THIRD ATTEMPT TO CORRECT MALFUNCTION IS CURRENTLY IN PROGRESS WITH NO MOVEMENT AS OF YET. GAS TANK HAS BEEN DRAINED AND REFILLED AND DID NOT CORRECT ISSUE. DEFINITELY NOT A GASOLINE TYPE ISSUE.