Guide by make
Reading the fault codes of a Citroën
Every Citroën sold in the EU has the EOBD diagnostic socket: gasoline cars since 2001 and diesels since 2004. With an OBD reader you read its generic codes, the same as on any other make; for the other control units you need to know how each platform is diagnosed.
Reviewed by Daniel Morales, founder of Reprorace SL, on
What a generic reader shows on a Citroën
With the ignition on, any OBD reader asks the engine control unit for its emissions diagnostics: fault codes, the data from the moment of the fault, live data and the inspection's readiness monitors.
The engine answers at the addresses ISO 15765-4 sets for every car with CAN: the reader asks 0x7DF (all of them) or 0x7E0, and the engine answers on 0x7E8. For the gearbox, ABS, airbag or body, the reader has to talk to each control unit at its own address.
Where the OBD socket is
The standard requires the socket to be within reach of the driver's seat. On almost every car it is under the dashboard on that side, sometimes behind a cover or next to the center console.
On your Citroën, the owner's manual shows its exact position. You do not need to remove anything to plug in a reader.
Known Citroën platforms and control units
CAN diagnostic addresses published by open sources, seen on the OBD socket. They may change with the model, the year and the equipment: take them as a starting point for the workshop, not as manufacturer data.
PSA platforms (CMP, EMP2, K9)
Platform shared with Peugeot, DS, Opel, Vauxhall, Fiat.
| Control unit | Request | Response |
|---|---|---|
| High-voltage battery (BMS) | 0x6B4 | 0x694 |
Open sources publish no more verified addresses for this platform: the rest is in the manufacturer's service information.
Sources: opendbc (© 2020 comma.ai, MIT license), OBDb (CC BY-SA 4.0) and OVMS 3 (MIT license), reviewed on 07-10-2026.
What the owner's manual explains
Some maintenance operations are done without a tool, from the car's controls. The manuals of these Citroën models (European editions) explain them:
- Maintenance reminder reset — Citroën Berlingo
- Maintenance reminder reset — Citroën C3
- Tire pressure monitoring (TPMS) initialization — Citroën C5 Aircross
- Maintenance reminder reset — Citroën C5 Aircross
Check the edition of your car's manual before following any step: they change with the model and the year.
Fault codes on a Citroën
A generic code, such as P0420 or P0300, means the same on a Citroën as on any other make: look it up in the glossary. A make-specific code (P1, for example) needs its service information.
Some of the most looked-up:
- P0300Random or multiple cylinder misfire detected
- P0301Cylinder 1: misfire detected
- P0171Mixture too lean (bank 1)
- P0172Mixture too rich (bank 1)
- P0420Catalyst system (bank 1): efficiency below threshold
- P0401EGR A flow: insufficient flow detected
- P0442EVAP system: small leak detected
- P0455EVAP system: large leak detected
Frequently asked questions
Does a generic OBD reader work on a Citroën?
For the engine's generic codes, yes: it is emissions diagnostics, the same on every make. For the other control units and service functions of a Citroën, the reader has to know its protocols and addresses.
What do P1 codes mean on a Citroën?
They are the manufacturer's own codes: the same number may mean different things on another make or model. Their meaning is in the official service information.
Is every Citroën diagnosed the same way?
No. According to our sources, Citroën uses these diagnostic platforms: PSA platforms (CMP, EMP2, K9). Each model may have its own control units and functions.
Read your car's fault codes on your phone
See the ECO-LITE page or buy it in the shop at the final price.