OBD fault code library
Look up any P or U code to see what it means, what causes it, the parts involved and how it gets fixed.
Free on OBD DashX
Looking for real-world repair data?
OBD DashX shows which problems come with each code, how often they show up in other vehicles, and how to fix them — step by step.
- Real-world fix data
- How often it happens
- Step-by-step repairs
Fault codes
P1421
Secondary Air Injection Valve Circuit Short To Ground
Volkswagen
Auxiliary Emissions Control
Medium severity
P1423
Bank 1 Secondary Air Injection System Output Too Small
Volkswagen
Auxiliary Emissions Control
Medium severity
P1428
Brake System Vacuum Pump Activation Short To Ground
Volkswagen
Vehicle Speed and Idle Control System
Low severity
P1429
Brake System Vacuum Pump Activation Open Circuit
Volkswagen
Vehicle Speed and Idle Control System
Low severity
P1431
Brake System Vacuum Pump Activation Open Circuit/Short To Ground
Volkswagen
Vehicle Speed and Idle Control System
Low severity
P1433
Secondary Air Injection Pump Relay Circuit Open
Volkswagen
Auxiliary Emissions Control
Medium severity
P1439
EGR Potentiometer Error in Basic Setting
Volkswagen
Auxiliary Emissions Control
Medium severity
Scan your own car
Read and clear fault codes, live data and service resets with the CaRPM app.