I've been chasing a problem on my sons '98 explorer. Check engine light came on. Hooked up OBDII reader with live scan. Read error codes 0171/0174 which are lean codes for banks 1&2. Ran live data scan to check long term fuel trims and bank 2 was at -100%. Checked ALL four O2 sensors and all of them are at 0.0 volts. Have checked all vacuum lines and no leaks. But, what makes me suspicious is reading of 0 volts. We should be able to get some voltage.

Am going to check for manifold gasket leak but engine runs smooth at idle. Any thoughts out there? thanks in advance

 

Your 98 might be different, but on my 97 the only things wired to mini fuse 11 are the 3 02 sensors. If your owners manual shows "hego system" check that fuse.

The fuse is in the power distribution box.

 

I see you must have the sohc, or a V-8 but it's still mini fuse 11 (15 amp) wired to the 4 02 sensors.

 

Thanks for the responses. I should have stated that I checked the fuse. Fuse is good, verified voltage at the fuse and at the output of the fuse as well.

 

Now that i think about it the voltage from fuse 11 is only used to power the 02 heaters to bring them online sooner.
The output voltage is generated by each sensor & is only around .1 to .8 volts or thereabouts. Each 02 is wired to a seperate pin on the PCM. Why your scanner is'n't seeing any output voltage is a mystery to me.

But if the codes are correct the common point for lean on both banks would be the MAF sensor. I would try cleaning it & go from there.
Some Ford engines have a common problem with a vacuum leak at the PCV valve. That would cause it to be lean on both banks also.

 

Another thing to check with lean codes is fuel pressure and checking it is VERY simple. Theres a valve in the fuel line that looks like a tire valve. screw a gauge on and see what you come up with.

 

I've checked fuel pressure, 35 lbs. solid (new pump about 2000 miles ago). Checked PVC hose and valve, all functioning ok.

Bought MAF cleaner yesterday and will try that tonight. Thanks again. I appreciate the info.

 

Yeah, with good fuel pressure & no vac leaks cleaning the MAF just might do the trick.

 

regardless of what the engine is doing, the O2 sensors should be displaying a varied voltage fluctuating above and below .450V

If they are completely dead, then you need to start by looking for voltage at the wires to the O2 sensors first. It's unlikely that all 4 sensors have died at the same time. Also, double check your readings by checking in global OBD instead of vehicle specific, just to make sure they aren't reporting improperly to the scan tool for some reason. There should be power to the O2 sensors with the key on engine off. If you aren't getting that much, then the heater circuit isn't getting power and you need to look into that first.