VW Code 13977

13977 Description And Summary :
The problem is about fuel mixture control adjustment range 1, higher limit not reached retarded timing position, the engine might refuse to start exhaust gas temperature sensor bank 1 sensor 2, circuit also nox sensor heater sense bank 1, circuit range / performance will delay your vw fault.

13977 Possible Causes:

13977 vw fault code may be caused by one or more of the following:

Inspect all the connections oxygen (lambda) sensor b2 s3, signal shorted to heater circuit
Check the engine oil to ensure it's clean and the viscosity
Restart the vehicle and retest to see if the error returns