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
P1820
Transmission Transfer Case Clockwise Shift Relay Coil Circuit Failure
Transmission System
High severity
Scan your own car
Read and clear fault codes, live data and service resets with the CaRPM app.