A while back I saw a thread with a link to the BAT Auto Technical Code listings. It is a good article in terms of how to obtain the fault codes using the various interfaces on the car.

My particular car is a 1990 300 SEL. I have been successful using some of the more obvious codes to troubleshoot problems such as a bad EGR valve which corresponded to a specific fault code (16).

My question is how do you corellate the more obscure codes or codes that appear in combination to actual fault procedures? Is there a cross reference that has this information or do you have to develop your own approach based on automotive systems knowledge?

Just today I got two faults codes together: F/C 11, Air Injection System; and F/C 17, O2 Sensor Signal. I'm not sure where to begin troubleshooting. I know I can check the O2 sensor duty cycle on the test connector X11/4 on the left fender but how does that relate to the Air injection?

Thanks for the help,
Motorhead