Hello All,

The Check Engine Light came on my 1990 300E Base Model, 3.0L.

I have a California Model so it consistantly blinks Code 17 or Code 18, occassionally both.

I replaced the Oxigen Sensor and the Idle Air Control valve - nice new components. This didn't fix it. I adjusted the air fule mixture with a DVM until I got half the battery voltage. This worked fine for about 10 months, no Check Engine Lights.

This week the Light came back on with the same 17 or 18 code displays. However, this time I only get 6.12 volts between pins 2 and 3 of the X 11 connector with the key on and the engine running or key on with engine not running. The mileage is pretty much the same, about 17.8 mpg and runs fine.

I swapped overvoltage protector, as I had a spare and nothing changed in the voltage.

What can be causing the voltage to drop in half like that?

Thanks