[ZeroBoyWD]

1998 3.8 V6

I tried doing a few searches but I can't seem to find an answer to my issue.

Ok so a while ago I get a check engine light and pulled codes P0135 and P0155, both upstream 02 sensors fault. Since I had to replace both the downstream sensors 6 months back I figured it was much the same.
So I replaced both of them and left my battery unhooked for five minutes before taking it out, then pulled 4 codes:
P0135, P0155 and I don't remember the other two (Said I was running lean)

Replaced my fuel filter (Def. needed it), Cleaned out my air filter and MAF, fuel injection cleaner, checked my fuel pressure (38 PSI) and checked for leaks (couldn't find any, unless I'm looking in the wrong place).

Got the check engine again but I figured I hadn't driven enough to complete the test (Work has a tendency to cut my car time short) so I drove it for another tank (Not at once). Light was still on, only pulled the P0135/155
codes.

Left the battery unhooked again then took it out for an hour and a half drive, light stayed off the entire time. Shut the car off, took care of my DPS stuff, then started the car back up. No light. Drove ten feet, light came back on.

Still pulling only the 135/155. Not sure it makes a difference but I'm using my girlfriends Actron ODB-II PocketScan to pull the codes.

My inspection is up next week and I'm really trying to figure this thing out. Any help is greatly appreciated

[MustangLX-5.0]

Sounds like you either got a wiring problem or a blown fuse. It's definately not the O2 sensors. The codes indicate there is a malfunction in the upstream O2 sensor heater circuit. Meaning, the heater circuit within both 02's is either getting too hot (overload) , not getting hot enough or not getting any voltage signal at all. This could be a constant ongoing problem, or it could be intermittent. If intermittent, there could be a loose harness that momentarilly disconnects, or badly pinched or cut wire someplace. Constant, then it could be a blown fuse. The heater circuits are on a fuse, but the exact one I'm not sure. Let me look that up and Ill get back.

Does everything else in the car work? Gauges, indicator lamps, AC interior fan etc?

[MustangLX-5.0]

Well that rules out a fuse for the O2 heaters. Only the 94-95 5.0's have the fuse.

[ZeroBoyWD]

So you think i need to get a voltmeter and check out my wires? I should have mentioned that, yeah, it gets very hot under my seat. The floorboards are really hot after running for 20 minutes. Not burn you hot, just where you know that something is amiss.

[Skymarshal]

Do you have any drivability issues? It almost sounds like you have unburned fuel downstream from the engine from a misfire or stuck injector or some other issue. That would overheat your O2 sensors and the residual fuel will burn in the catalytic converters, creating the heat you say is abnormal. Try having someone hold the engine at a mid rpm while parked and see if it looks like the cats are getting unusually hot.

If no drivability problems, then a wiring problem is what I would suspect...