What is OBD2?
OBD2 is the standard diagnostic system in nearly every petrol and diesel car built in the last 25 years or so. It lets one adapter read the engine computer of any car that has it: the fault codes, the readings, and the results of its own emission self-tests.
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What OBD2 is
OBD stands for on-board diagnostics. While you drive, the engine computer checks the systems that affect the exhaust emissions. When it finds a fault, it turns on the check engine light and stores a fault code.
OBD2 is the standard that makes this readable from outside: the same 16-pin socket within reach of the driver’s seat, the same small set of communication protocols, and the same requests and codes on every car that has it. That’s why one adapter and one app can read cars of very different makes.
EOBD is the European version. It uses the same socket and protocols, and as a rule it’s required on petrol cars from 2001 and diesels from 2004 in the EU. In the US, OBD2 is required on cars and light trucks from model year 1996.
How the car talks
Most newer cars use CAN, a fast network. Many older European cars use the slower K-line protocols (ISO 9141-2 and KWP2000). The adapter in the socket finds out which one your car uses and translates for the app.
What it can read
The standard defines a set of services, each for one kind of information. Read My Car uses these:
- Stored codes
- Confirmed faults. Usually the check engine light is on with them.
- Pending codes
- Usually seen once, and stored if they happen again.
- Permanent codes
- On cars that have them: faults the car hasn’t yet confirmed as repaired. They can’t be cleared with a scan tool.
- Freeze frame
- The readings saved when a fault was set.
- Live data
- What the engine computer sees right now, such as engine speed, coolant temperature, fuel trim and battery voltage. Only the readings your car reports are offered.
- Emissions readiness
- Whether the car’s emission self-tests have run since the codes were last cleared.
- Vehicle information
- The VIN, where the car reports it, and on some cars the engine computer’s name.
Clearing the codes is a service of its own. It also resets emissions readiness and erases the freeze frame, so Read My Car asks you to confirm it first.
What it can’t read
The rules only require emission-related data. So generic OBD2 reaches the engine and often the gearbox, but not the rest of the car.
- ABS, airbag, body and comfort modules use the manufacturer’s own protocols and need a tool for the make, even though many cars use the same socket for them.
- Manufacturer-specific codes (such as P1xxx) can be read, but their meaning depends on the make and model.
- Read My Car reads and clears; it can’t run actuator tests, regenerations, relearns or coding. Those need a tool for the make.
Reading a fault code
The first letter is the system: P for the engine and gearbox (powertrain), C for chassis, B for body and U for communication between modules. Codes starting with P0 or P2 mean the same on every car.
Questions
Is EOBD the same as OBD2?
Practically, yes. EOBD is the European requirement, with the same socket, protocols and generic codes. A tool that reads OBD2 reads EOBD.
Can OBD2 read ABS or airbag faults?
Not generic OBD2. It reaches the engine and often the gearbox. ABS, airbag and body modules need a tool for the make.
Can reading the codes change anything in the car?
No. Reading is harmless. Clearing the codes does change something: it resets the emissions self-tests and erases the freeze frame, which is why Read My Car asks you to confirm it.