Audi , A6 , C4 , 1.9 TDI (1994-) Common Issues

Faulty oxygen sensor(s)
Leak in the timing belt
Worn or loose serpentine belt tensioner bearing
Vacuum leaks on intake manifold gaskets or connections
Cracked engine head or block due to overheating
Worn piston rings causing low compression
Faulty MAF (Mass Air Flow) sensor
Water leak in the cooling system, particularly from the heater matrix connections
Rusted or corroded brake master cylinder and/or brake lines
Rear main seal weepage due to worn-out or damaged seal
Cracked exhaust manifold on either bank
Faulty EGR (Exhaust Gas Recirculation) valve(s)
Clogged fuel filter or clogged DPF (Diesel Particulate Filter)
Worn-out or loose engine mounts causing vibrations and noise
SRS airbag system light staying on due to faulty sensor or unit
Faulty transmission solenoids or faulty ECU programming for the transmission control module
Cracked cylinder head(s) from thermal stress or previous repair attempts
Rust-through in critical areas such as brake lines, exhaust components, and suspension components
Faulty wheel bearings causing vibration on one side of the vehicle
Oil leaks due to worn-out or damaged oil seals and gaskets