Hello everyone,
You all helped me with my ailing 1994 Park Avenue that runs great now thank you! However, every now and again I'm getting the 18X signal failure code; only at start up and if I turn the car off and start it again it isn't current. I wonder if this doesn't contribute to my wierd gas mileage. My Park Ave. with the 3800 series is getting 28-30 highway and 18-20 around town. It seems like a huge difference to me and was wondering if something was causing this? My 1994 9C1 driving the exact same routes gets 19-22 highway and 15-18 around town. Thoughts?
Thanks, Bryan

I believe the code you are referring to comes from the crankshaft positioning sensor. If it is not a hard code I would say that somewhere along the circuit there is a fault. Check the circuit first then check the sensor itself. Through research (not quoting this) you would also be recieving a 3x signal code if the sensor was bad.

I'm not 100% sure we can say the 18X might be missing and the 3X should automatically be missing. This sensor contains two paths for the signals..it'* possible one is bad and the other is still functioning. Unless the +5V is missing from both.

The mileage sounds on the mark to me. Mileage depends on your city driving. A person living in NYC is going to get poor mileage while someone in Enfield CT (both being cities) will get much better mileage.

OK thanks guys,
I guess the gas is nothing to worry about and I'll troubleshoot the crank sensor. When I start the car up and the light comes on the car shifts a little different than when the code is not present. I tested this when the light was on the car was shifting at higher than normal RPMs and rougher than ussual. I put it in neutral shut it off, started it again and no light and no odd shifting. The code only seems to occur if I get in and start the car immediately; if I get in and wait like 1 or 2 seconds it doesn't come on.
Thanks, Bryan