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How to connect a scan tool
VW and Audi Diagnostic Trouble Codes and data can be retrieved with VW/Audi factory scan tools such as the VAG 1551, VAG 1552, or the diagnostic computer VAS 5051, through a Data Link Connector (DLC). Several aftermarket scan tools and computer programs are also capable of retrieving this information in this factory mode. The factory mode also allows the scan tool to be used for other system diagnostic functions and information retrieval.
Some DTC information can also be retrieved in a generic mode. The generic mode is not as complete as the factory mode, but allows commercially available scan tools to be used simply to read DTCs. Generic scan tool mode does not have the capability to retrieve the detailed information of a manufacturer-specific scan tool.
Volkswagen technical library
The Volkswagen technical library → — articles by car, maintenance schedules, and the fault-code lookup.
Scan tools
Scan tools and where to get them → factory and aftermarket, with the supplier list.
Then decode what it shows
Decode an OBD II fault code (1996 and later)
OBD II, model year 1996 and later: enter the P-code your scan tool displays (P0420) or the five-digit factory number (17828). Cars of 1990–1995 use the earlier system — see the Volkswagen Scan Tool Companion.
The code page: any of 774 codes, with the P-code key →
How a P-code is built — the full key
First digit — the system
- Pxxxx — powertrain
- Bxxxx — body
- Cxxxx — chassis
- Uxxxx — future systems
Second digit — who defined it
- P0xxx — Government required codes
- P1xxx — Manufacturer codes for additional emission system function; not required but reported to the government
Third digit — the subsystem
- Px1xx — measurement of air and fuel
- Px2xx — measurement of air and fuel
- Px3xx — ignition system
- Px4xx — additional emission control
- Px5xx — speed and idle regulation
- Px6xx — computer and output signals
- Px7xx — transmission
- Px8xx — transmission
- Px9xx — control modules, input and output signals
The fourth and fifth digits designate the individual components and systems.
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