Date registered: Aug 2002
Vehicle: '85 2.3-16 '99 C280 '11 GLK350
Location: Scottsdale, Arizona, USA
Mentioned: 0 Post(s)
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RE: Testing oxygen sensor - 89 300e
Using a digital voltmeter with reasonably high impedence (20K ohms or so), you can measure the voltage output of your O2 sensor while it's connected to the computer, with the car warm and running of course. Just find the single wire connector coming from the sensor that goes to the computer - not the one that has two wires, that's the preheater on some sensors. Set your meter to a range near 1 volt - the sensor's output falls in the 0-1 volt range. Ground the (-) probe to a chassis ground or the battery, and clip the (+) lead to the sensor output. You should be getting a reading in the neighborhood of 0.45 volts, fluctuating a bit up and down. If you get no voltage or a low voltage, your sensor needs replacement.
BTW, the 300E (and the 190E) uses the same Bosch sensor that's used in the BMW, Saab and Volvo. But more importantly, it's the same as the sensor for the 1990 Ford Mustang 5.0L V8 (Bosch PN 13942) which has the requisite metric threads (with a little Anti-seize already on them). The only differences between the Ford sensor and the Mercedes sensor is 1) the end connector; 2) name of the car it goes into - based on the salesman's computer database; and 3) PRICE!!!!!
If you're buying the sensor from a non-Ford parts dept (Autozone, NAPA, PepBoys, etc.) they may tell you they have more than one sensor for the Mustang application, since Mustangs had two sensors, so don't let the parts guy sell you two for your non-existent pony car.
The sensor is the three-wire type, (with two white heater wires), To fit, cut off the Ford connector and solder the existing Mercedes connector on to it (while matching wire colors), and install. .