Diagnostics basics
Which diagnostic protocol does my car use: CAN, K-Line or DoIP?
Most current cars are diagnosed over CAN, on pins 6 and 14 of the OBD port. Older ones use K-Line on pin 7, and some recent models open part of their diagnostics or programming over Ethernet (DoIP). A reader that detects the protocol by itself saves you from finding out.
Reviewed by Daniel Morales, founder of Reprorace SL, on
How has the protocol changed over the years?
Early on, OBD allowed several protocols: K-Line (ISO 9141-2 and ISO 14230, also called KWP2000), CAN (ISO 15765-4) and, mostly on American cars, SAE J1850. Over the years CAN took over at almost every brand.
A car can have several buses inside: the engine may answer over CAN while a comfort control unit stays on K-Line. The newest models add CAN FD, which is faster, and some manufacturers use DoIP to diagnose or program over Ethernet.
How can I tell myself?
One clue is which pins the port has: contacts on pins 6 and 14 mean CAN; on pin 7, K-Line; on pins 3, 11, 12 and 13, possibly Ethernet. But a pin being there does not guarantee it is used for diagnostics.
The reliable way is for the reader to detect it when it connects, trying each protocol in order. The manufacturer's service information also states it for each model.
What about trucks and some American cars?
Trucks, buses and a lot of machinery use SAE J1939 over CAN, usually at 24 V. Some GM and Opel models also use a single-wire CAN (SW-CAN) on pin 1.
That is why a reader should list exactly which protocols and voltages it supports, rather than promising “all makes”.
General guidance only: every manufacturer and model has its own details. Always follow your vehicle's manual and, if in doubt, ask a workshop.
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See what your car is saying
The ECO-LITE detects the protocol when it connects and speaks CAN and CAN FD on two channels, CAN on pins 1/9, K-Line, SW-CAN, J1939 and DoIP, at 12 and 24 V.
Presale price: €129 · US$129
Frequently asked questions
Can a car use several protocols at once?
Yes. It is common for the engine to answer over CAN while other control units use another bus or other pins of the same port.
What happens if my reader does not speak my car's protocol?
It will not connect or will only see some control units. It does not harm the car, but you will not read those faults.
Is DoIP only for electric cars?
No. DoIP is diagnostics over Ethernet and is used on combustion and electric cars alike, depending on the manufacturer and model.