Audi OBD Trouble Code 27

Sub-oxygen sensor signal or heater circuit fault

Fuel injection circuit control

Injector circuit isn't switching when it's told to (TBI)
(MPI) injector circuit #1 not switching right
(turbo) injector circuit #2 not switching right
(all 1990-) injector output driver

QDM A ( Quad-driver module ) - 2nd gear circuit

Injector # control circuit
Injector number # output driver circuit does not respond to the control signal. Check the affected circuit.