Date registered: Aug 2002
Vehicle: 190E, 400E, SLK350
Location: Chesapeak Bay
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Okay, here is my update.
I unplugged the CIS temp sensor and the reading between pins 2 and 3 jumped to a steady 9.8V. The pulse wave widened on scope accordingly. This tell me that without the temp sensor in circuit the CIS goes to the other extreme.
Basically one extreme resembles the wave with the ignition on and engine off even if the engine is warm, that is the DC reading is 2.9V. The other extreme is when the temp sensor is out which brings the reading to 9.8V.
The happy medium should be something in between with fluctuations due to the O2 sensor.
Having observed that I measured the resistance of the temp sensor while the car was warm. I got about 800 to 900 Ohms between the poles and 400 Ohms via ground.
Reading the CIS troubleshooting guide, I should have between 290 and 370 Kilo Ohms to ground.
I think the sensor is shot!