Hi Lugnut,
For once we agree!

Step 1. Read and record all available OBD info (eg Flash) and reset CEL.
Does problem return?

If CEL reappears

Step a. What codes are showing. The same?
Step b. What conditions prevailing when the CEL reappeared. Comparison with original occurrence. From "flash" or personal memory
Step c. Are the O2 sensors cycling correctly? i.e. voltage and cycle time.
,,,,,,,,

 

Hi Sleepwalker.
Please tell me a little more about this please.

........"in the case of S600 W220 for example, if the oil from pressure sensor goes up to the ECU, all O2 sensors registers the fault."

 

of course it never happen to other engine except S600 which i only make as an example.

whenever the B40/2 is faulty and leaking inside, the oil will easily go inside the wiring harness and other component's connector such as engine control unit, air mass sensor , knock sensor, oxygen sensors, ignition coils and cylinder shutoff.

many of these cases i have seen and can only be fixed by replacing the B40/2.

it's so strange on how the oil tunnels through the small and tight wires, but it does. sometimes you will find the engine control unit half filled with dirty engine oil

[IMG]local://upfiles/1/3489D9624C9541D18D7F12FD9855E1C9.jpg[/IMG]

 

Thanks Sleepwalker.
So the failure mode is oil in the ECU/Control Unit/Connectors.
Presumably the oil and possibly water will creep up the wire harness due to pressure difference between the ends aided by capillary action.
Very interesting.
Water tracking along the harness and causing corrosion at connectors / ECU is now my No1 cause for electronic problems.
In the UK any such water is usually contaminated with road salt (NaCl) which exacerbates corrosion.
Why don't the manufacturers squirt silicon RTV or similar to discourage this on harnesses which travel from wet to dry zones?
Think I may take this issue up with the industry somewhere.