Manufacturer-specific fault codes
A code such as P1351 or U1121 has no meaning that holds for every car: each make defines its own. What these codes are, why Read My Car shows the brand and its diagnostic tool for them, and how to find out what yours means.
Updated
How a fault code is built
Every OBD2 fault code has a letter and four characters. The letter is the system: P for powertrain (engine and gearbox), C for chassis (such as ABS), B for body (such as airbags and comfort electronics) and U for the network between the control modules.
The character after the letter says who defines the code. The standard for fault codes, SAE J2012, splits the ranges like this:
- P0xxx and P2xxx
- Generic: the same meaning on every car. These are the codes explained on this site.
- P1xxx, and P3000 to P3399
- Manufacturer-specific: each make defines them. P3400 and up are reserved for the standard.
- B0xxx, C0xxx, U0xxx
- Generic.
- B1xxx, B2xxx, C1xxx, C2xxx, U1xxx, U2xxx
- Manufacturer-specific.
- B3xxx, C3xxx
- Reserved for the standard.
- U3xxx
- Partly manufacturer-specific, partly reserved for the standard.
So P1351 on one make and P1351 on another can be about completely different parts, and even models of the same make can use a code differently.
Why Read My Car shows the brand and its tool
Read My Car identifies the make from the vehicle identification number (VIN), where the car reports it: the first characters name the manufacturer. For a manufacturer-specific code it then shows “Volkswagen code, not in the generic list”, for example, instead of guessing at a meaning.
Where a diagnostic tool for the make is known, the app names it: VCDS or OBDeleven for Volkswagen, Audi, Škoda and SEAT, Diagbox for Peugeot, Citroën and DS, Techstream for Toyota and Lexus, FORScan for Ford, and others. Those tools speak the brand’s own protocol and show the code’s description from the manufacturer’s data.
The app doesn’t judge the urgency of a manufacturer code: it shows “Severity unknown”, because the same number can mean a harmless fault on one car and a serious one on another.
How to look up a manufacturer code
- Write down the code exactly, and the make, model, engine and year of the car. The VIN pins down the exact version.
- Look for generic codes stored at the same time: they often point the same way, and Read My Car explains those.
- Look the code up in the service information for your car, or read it with the tool for your make. They give the manufacturer’s own description, and often the module’s live data.
- Searching the web for the make and the code helps too: in Read My Car, “Search web” in the fault’s details does that. Prefer a source for your model and engine, and be wary of a meaning found for another make.
- If you can’t find a reliable meaning, have a garage with the brand’s tool read it.
Can I keep driving?
The code alone doesn’t say. Go by how the car behaves: if the check engine light flashes, a red warning light comes on, or the car loses power, makes new noises or brakes or steers differently, stop when it’s safe to do so and get help. Otherwise, have it checked soon, especially if it might involve a safety system such as ABS or airbags.
Codes generic OBD can’t read at all
Generic OBD2 reaches the engine and often the gearbox. ABS, airbag, body and comfort modules usually answer only in the brand’s own protocol, so their codes, generic or not, need the brand’s tool. Read My Car says so on the Faults screen and names the tool where it’s known.
Fault codes explained here
- P0700Transmission control system malfunction (see TCM codes)
- U0100Lost communication with ECM/
PCM "A" - U0121Lost communication with anti-lock brake system (ABS) module
FAQ
What does the 1 in P1xxx mean?
That the code is manufacturer-specific: the make defines what it means, not the OBD2 standard. A 0 in that place, as in P0420, means a generic code with the same meaning on every car.
Why doesn’t Read My Car explain my P1 code?
Its meaning depends on the make and often the model, so a generic explanation could be wrong. The app shows the make and, where it’s known, the tool that reads the manufacturer’s description.
Is a manufacturer code less serious than a generic one?
No. The range only says who defines the code, not how serious it is. Go by the code’s real meaning and how the car behaves.