Hi, I'm new to this forum. I'd like some advice on making the O2 sensor warning light on the instrument panel turn off. The car at issue is a 1993 190E 2.3 automatic; this car is a "California emission" car. I was able to reset the warning light by pressing a button on a box in the passenger's foot well; however, a few seconds after the reset switch is pressed, the warning light would blink 7 times, pause, blink 6 times, pause, and stay on. The warning light comes right back on the next time I start the car. I've replaced the O2 sensor with a Mustang sensor and checked the air-fuel mixture. The voltage from the O2 sensor fluctuates from 0.2 volts to 0.8 volts. The X-11 pin 3 fluctuates at about 50% duty cycle. Thus, the O2 sensor and the air-fuel mixture appear to be good. Just today, I replaced the OVP relay out of desperation, but it didn't help. Now, I don't know what else to do. The car seems to drive fine, but I'd really like to make the light stay turned off. If something is faulty, I'll like to get it fix because something like this might affect gas mileage and I don't need to burn more gas than necessary--this little Benz requires expensive Premium gas. Thanks. Look forward to suggestions.

By the way, spark plugs, cap, and rotor were recently replaced--after the O2 sensor light problem. The ABS warning light is also On all the time, but I don't really care about ABS and unplugged the ABS computer completely.

When the O2 light blinks it is probably calling off fault codes 7 and 6. You will have to check the service manual to find out what they mean.

I believe these may be the correct codes.

Code 6 - Idle speed control faulty
Code 7 - Ignition system faulty

Do you have the original engine wiring harness? This may be your problem.

The ABS warning light may be attributed to a faulty brake switch above the brake pedal.

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95 E320 Cabriolet, 159K

Yes, I do have the service manual. However, I can't find anywhere that gives the O2 sensor light blink code. It has blink code for the diagnostic LED in the engine compartment next to the battery, and it has a diagnostic table for the X11-pin 3. But nothing about O2 sensor light; all the manual says is that the said light will come on the the system detects a problem with the O2 sensor.

Hi Kestas,
Where did you find those codes in the Service CD?

If the Idle speed control is faulty, wouldn't the idle RPM be off? Mine is perfectly fine at 800 rpm.

How should I begin diagnosing a faulty Ignition system?

Thanks all,

ks2004
1993 190E 2.3 Auto