My car has been putting out a little black smoke and using too much gas since I got it. The CEL has never come on and the scanner revealed no codes.

I put the scanner back on it this morning and looked at Live Data and the first bit of data said, "Fuel Sys 1 CL-Fault" which means it's running in closed loop. I checked the MAF and ECT and was fine and was looking around in the engine compartment and noticed the wire to the coolant level sensor under the reservoir was disconnected.

Now the scanner shows the ECU is in open loop mode and the engine is no longer puffing black smoke and is more powerful.

Is it normal for low coolant or a disconnected wire to the level sensor to keep the ECU in closed loop and put out no DTC's?

I was lucky to spot it because I had no idea to look there other than just browsing all the engine compartment.

 

If the wire was grounding out, it is very much possible. I would not worry to much and just be happy you fixed it.