Error code reader
Many of the ECUs in the XM can store and replay error codes when asked. Usually, they are read and cleared using the Lexia diagnostic system originally used by the dealer garages (copies of this system are available on the Net from Chinese vendors now).
Although the Lexia is much more capable than a simple error code reader (it has access to all vehicle susbsystems and can not only check stored errors but measure many parameters and actuate various parts), there are times when a simple code reader can also be of help. It's very easy to build such a code reader for Series 1 XMs and it's even easier on the Series 2 because all you need is a piece of wire. On both cars, you need to connect a specific pin of the diagnostic connector to the ground. However, Series 1 has the connectors inside the ECU box in the engine bay, Series 1 houses them nicely behind a flap under the steering wheel. On the Series 1, a LED with a series resistor will display the codes. On the Series 2 you don't even need the LED: the dashboard diagnostic light will do the same.
There are four ECUs to read out: engine, suspension, air conditioning and ABS. The process is always the same: turn the ignition on. Within three seonds, connected the appropriate connector pin to the ground for 3 to 5 seconds. The LED or warning light will display the start code 12 (by flashing once, pausng a little and flashing twice).. Now proceed with the wire, connect it to ground again for 3 to 5 seconds, and the error codes will appear one after the other, always using the same pattern: flashing for the tens, pausing, flasing for the ones. You reach the end when the end code 11 is displayed.
At this point, you might clear the accumulated codes by connecting the pin to ground for 15 seconds.
Easy. But the connector is deep down, you have to locate the pin, the warning light is up on the dashboard and you have relative tight timings to ensure. So, if you plan more than trying out once for the fun of it. it pays off to build a little tool to help with the testing.
As there are four ECUs to read, we can have four pushbuttons in a little box, all wired to the corresponding pin, ready to connect to ground. The schematic is so simple it hardly needs description:
All that can be housed in a little box. You can buy a Lexia replacement cable cheaply online and use its connector.