Warning! Long post. I have to consult the brain trust on an item that's got me, as well as two repair shops, very frustrated with my 2013 Expedition Limited with 5.4L three valve engine. I've got about 165000 miles on the odo.
About a year ago a heater hose burst and soaked the passenger side of the engine compartment with coolant. After repairing the hoses I had a misfire on #1 cylinder. I replaced the coil to remedy. That day my check engine light came on with codes P0135, 141, 155 and 161. All these codes refer to O2 sensor heater malfunction. I replaced all four of the sensors W/O remedy. Also my fuel mileage took a nosedive from 18 MPG to 13.
Frustrated I took the car to a shop that had good reviews on the internet. I advised them of the events which led to the CEL coming on. As I expected they told me I couldn't use aftermarket O2 sensors so they installed Ford sensors. They also cleaned the intake system with some sort of a pressurized device. Still no remedy. Now they're saying the cats are plugged. The O2 sensor repair cost me $1400 and now they want another $2000 to do the cats. The cats do not inhibit acceleration, it still sets you back in the seats when you hammer it.
The ECU probably got soaked from the heater hose failure being right there on that side of the engine. I'm thinking The ECU is the problem but I hesitate to replace the ECU without some way to confirm my suspicions.
I would appreciate any comments on this issue.

 

Sounds like you got water(coolant) where it isn't supposed to be. Like the ECU connections at the firewall on "the passenger side of the engine compartment" for starters. I've had water issues with my o2 sensor connections as well, though it was on an '07 F150. For Zero money, disconnect battery. Touch positive and negative cables together(after they are disconnected) to erase memory. Then disconnect ECU and thoroughly clean/blow out connections. Look at all the pins to ensure cleanliness and positive connection. The negative battery cable should be the last thing you re-connect. It will take a while to re-learn how to run right.
My wife drives the same vehicle and it's finicky as heck with electrical stuff; especially the battery. I've had it do the most bazaar things never imagined because of battery voltage.

$1400 sounds high for O2 replacement but depending on where you live maybe. I highly doubt the converters are bad. I would take it elsewhere for another $100 opinion.

Fixing electrical issues can be a crapshoot. Most shops don't like them because it is potentially a rabbit hole that may not have a bottom. There's often other more lucrative work to be had, especially now when everyone is getting geared up for summer trips. A/C. tune up, trans service, etc <-- Gravy work $$