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It's not so difficult...
You want to measure the voltage between pins 2 and 3 at the X11 connector (drivers side of the engine bay - round, black plastic, screw off top)
Since your multi meter does not read duty cycle you: [1 - (V{pin 3}/V{max})] x 100% = Duty Cycle
When I read duty cycle I have to put the + terminal of the multi-meter in pin 2 and the - terminal in pin 3 or I get an inverse reading.
I have never tried it reading DC Volts and dividing by the max voltage... so I'm not sure which way you align the poles to obtain the correct reading. To determine which way to align the MM you should first take a reading, engine off, key turned to on position (assuming your car is not a california car)... then your equations correct answer should be 70% constant voltage (85% for california)
When you do the actual test your Engine should be fully warmed up and ideling...
If the reading fluctuates the o2 sensor could be functioning but may still be bad (lazy or out of range) note what voltage the reading starts at and where it moves to over about 5-7 minutes time.
If the answer is a constant 50% the o2 sensor is definatly bad
Post your results if you have any problem interpeting them or get unexpected results...
P.S. If you end up replacing o2 sensor you can solder a 1990 mustang 302 sensor (about $40.00 US) onto your existing connector and save $70+ over mercedes OEM.
P.S.S. I hope all my info is correct, if not I hope someone will jump in and correct it.
Last edited by A264172; 12-16-2005 at 09:21 AM.
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