W203 A209 CAN BUS junction access made easy.

[hofnerpres1]

Whilst chasing the all too common no key turn - no start fun and games, the need will arise to monitor and measure the voltages, resistances at the point where all the engine CAN C feed wires to the modules meet - X63/4 which on the RHD W203 chassis is incarcerated in the RH sill wiring channel right up front by the accelerator pedal. Remove the fixing screw in the centre of the side trim panel and wrestle free. The sill cover is just held down by rather hefty clips so carefully lift it from the front and ignore the sound of tortured plastic - it can be a pain. Grovel around inside the channel and find the 100mm long black box with all the Green and Green/White twisted wires coming from it. The individual plugs do release on neat clips so it's easy remove a few which will allow you to release some from the knitting pattern that the factory created - this will then allow you to reposition things much closer to yourself and do some diagnosis. The odd man out is the three pin one - the brown is an earth and this GN GN/WH pair go to your ECM. There is still a problem getting safe access to all the tiny pins so get onto ebay and order a pack of JSL male and female two pin connectors which we model aircraft folks use to connect One Cell Lipo packs. They are a perfect slide-on fit on the spare sockets at the junction. For maximum points, use them to make an extension lead and leave the small female socket end poking out from the re-assembled side panel. Instant access to the most vital system on your car. It's doubly useful on a Mercedes since the CAN C output at 4 and 16 on the OBDII port is behind a gateway in the Ignition module Black Box of Death ( EIS )- Voltage and resistance readings are futile - it just outputs code which only your scanner can read.