Connecting to a car with ODB-II

Our Opel/Vauxhall Corsa B (engine X10XE, 55KW, 1.0l, 12V) has a problem: it lights up the MKL (“Motorkontrollleuchte”, the engine control/warning light) when we’ve been trying to accelerate on the Autobahn. In order to diagnose the problem, I wanted to connect to the on-board control unit and read the error code. Unfortunately, connecting to this unit proved to be a mess. It took me a while to realize that we have the only model of Corsa B where you cannot read the error code with a paper clip: the car has a modern interface standard to all cars nowadays, called ODB-II. You cannot read ODB2 data directly, you have to connect to it using a computer.

OBD-II adapter from for connecting to the onboard control unit of many cars. For Opel/Vauxhall, you have to us a multiplexer to switch between different pins. On the left, the ExpressCard adapter that allows to connect without timing problems.

The reader required for this can be quite costly – a couple of thousand Euros for the top-of-the-line standalone units. Well, I wasn’t keen on spending more than my car is worth, so I bought a Open Hardware/Source kit from Amazing site with really knowledgeable, helpful people. I’ve paid ~20€ for the kit including cable, casing etc.

Unfortunately, the interface needs a serial port ans is extremly sensitive to timing (as so many low-level programmers/adapters are). But who the hell still has a real serial port on their laptop? I ended up buying severals adapters just to realize that anything USB-based does not work, and that most extension cards for laptops are based on cheap USB-to-serial adapters. Obviously, ExpressCard/PCIe<->USB<->Serial does not have the best timing properties. I found one chipset that does real PCIe<->Serial conversion, it’s the Oxford OxPCIe952. Any card based on this chipset should work with the ODB-II adapter mentioned above (and any other as far as I can tell). I payed about 20€ for the ExpressCard on eBay.

With the adapter, I managed to connect to the engine control unit alright, which allowed to read and delete the error code (P0103). Now I just have to find the reason for this error code…

PS: There’s unfortunately no open-source project for Opel available, but there is a demo version of the common OP-Com software. The ExpressCard adapter works out of the box with Linux (Ububtu 10.4) and Windows (XP).

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