DTC Audi P0491 Short Explanation

The video focuses on the basic Audi diagnostic error code.
Contents:
0:21 Basic DTC analysis according to OBD2 protocol standard.
1:48 Insight into programming
- an explanation of what a bit is and how a byte is formed
- decoding the Error Code to the base programming
2:58 A diagnostically understandable description of the Diagnostic Trouble Code
3:05 Basic error definition
- Possible causes or errors of the car and its parts describing the mentioned error

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Make:
Audi
Code:
P0491
Definition:
Secondary Air System Insufficient Flow. flow check during cat. heating. PZEV only
Description:
mass air flow, 7.. .150kg or h Delta engine load, -10.. .10% rev ECT, 5.. .60° C IAT, 5.. .40° C altitude, lower then 2700 m SAI pressure sensor, ready no fault.
Cause:
Check for signal, voltage and ground
Check harness for open or short
Check connector for damage.
Replace ECM