What a fault code means
How to read a code: letter, status, severity, warning lamp and indicative explanation.
Reviewed by Daniel Morales, founder of Reprorace SL, on
Each fault has a code (for example P0420) and, when you press it, its sheet with the description, the indicative severity, the typical causes and the sources from the diagnostic library.
| Code letter | System |
|---|---|
| P | Engine and transmission |
| C | Chassis |
| B | Body |
| U | Communication network between control units |
| Status | What it means |
|---|---|
| Active | The fault is present now. |
| Pending | The control unit has seen it once and is watching it; it has not confirmed it yet. |
| Stored | It was recorded; it may no longer be present. |
| Permanent | Only the control unit itself clears it once it checks that it has been fixed; clearing faults does not remove it. |
| Previously active | It was active and no longer is (trucks and machinery). |
- Generic or manufacturer code: a generic code means the same in every make; a manufacturer code only in its own.
- Warning lamp on or off. On J1939 trucks: “Stop (red)”, “Warning (amber)” or “Protection”.
- On trucks and machinery the code is given as “SPN n · FMI m”: the SPN says which part or value and the FMI how it fails.
Important: The description is indicative: confirm it with the manufacturer's information before replacing parts. If you see “Not yet translated into your language”, the sheet is in the language of its source.
Tip: With the red lamp or “Stop (red)”, stop the vehicle as soon as it is safe and contact your workshop.
More guides in this section
- How a remote session works
- Tunnel plan: connect a tool to the vehicle remotely
- Accept or withdraw remote access to your vehicle
- Collaborating in a session: messages, prompts and photos
- Unit PassThru mode from the app
- PassThru on Mac, Linux and iOS
- Assistance requests, appointments and work orders
- Legacy vehicle configuration and diagnostics: VAG and other makes
- Modern vehicle coding and programming
- Automatic diagnosis: one tap and it explains
- Reading a vehicle and sharing the report
- CANopen diagnostics for machinery
- Vehicle details: identifying it by the VIN
- Live dashboard, service functions and battery test
- v2 procedures: beta and operational
- Compatibility notices for your tool
- CAN captures
- Pre-purchase report
- Battery health of electric and hybrid cars
- Asking Diaglana for help
- Your first read: understanding the result and what to do
- Diagnosis options: each setting and when to change it
- Workshop settings: requests, orders, network and notices
- Reading: choosing the protocol and understanding the OBD on UDS report
- Live data: dashboards, recording and export
- Attaching fault codes to a work order
- Procedures that write, program or authenticate
- ISOBUS: reading and changing an implement's NAME
- Diagnosis over Ethernet (DoIP)
- Download Diaglana PassThru for Windows, Mac and Linux
- Authorizing a PC for PassThru
- Diaglana PassThru updates