How do l get low def lite,no start counter and code 16cf00,18b400,15b700,131e00,17900 to reset.

The error code 520538-4 indicating a short circuit to ground in the DEF heating element is a serious issue and can affect the performance of the vehicle. The DEF system is critical for the vehicle to meet emission standards and should be addressed as soon as possible.
Since you have already replaced all of the DEF system components and even the ECU and the problem still persists, there are a few other things that you can check:

1. Wiring harness: Check the wiring harness that connects the DEF heating element to the rest of the vehicle's electrical system for any damage or loose connections.
2. DEF Pump: The DEF pump may have a failure that causes the DEF not to flow properly.
3. DEF Dosing Unit: Check the DEF dosing unit for any clogs or damage.
4. DEF Quality: Make sure that the DEF being used is of the correct quality and specification.
5. Software update: Check with the dealer or the manufacturer if there is any software update available that can fix the issue.

It's highly recommended to have a professional technician diagnose and fix the problem as it's a critical emission component and might cause further issues if not addressed properly. The technician can use a diagnostic tool to check the system in more detail and locate the exact problem.

I would think the def level sensor is not operating properly.

I doubt it but that is just my opinion

I would suggest it may be a dirty or clogged fuel filter or gas tank sending unit inside the gas tank. Try replacing the fuel filter first, if that does not work, you may need to pull the gas tank and clean it. God bless your efforts.

Highly doubtful. You're best off taking it in to have the codes read to find out what your transmission problem truly is.

This problem in a Ford is caused by a defective fuel gauge sending unit inside the fuel tank, the tank must be removed to replace the sending unit.

Hi: It Sounds like you Either Have a bad Connection on Your Gauge or the Sending Unit which is in Yout Gas Tank.Your Fuel Pump and Sending Unit Are Located In Gas Tank.Check and Make Sure your Connections are Good and Clean 1st. But it Really Sounds like your Sending unit has Gone Bad.To Replace Sending Unit You'll Have to Drop The Fuel Tank,Empty As Much Fuel as you Can Either Drive till its empty. Holding your Tank Up is 2- Metal Straps with Threaded Bolts and Nuts, Spray with WD-40 And Let It Set awhile Cause Normaly the Are Dirty. Then Take Eiter A Deep Well Socket if it will reach the Nuts,Or Use A Wrench -Remove BOTH NUTS And also at the Filler Tube You'll Probally have a2-3 Screws you'll need to Take Out. Your Tank Should Come on Down.NOTE: Don't PULL the tank out Until you take your Wire Connects Off Remember Which ones Went where. Then Slide Tank out Away From Vehicle, On The Top Of Tank where you remove the wires where thers a Metal Retaining Ring, You'll need to Spray with wd-40 and Remove that Ring,Buy taking a Screw Driver and small Hammer and Tap it out Going Counter Clockwise. After its Off you will be able to Remove the Complete Fuel Pump Assembly. All you'll Need is to Remove Sending Unit.Since Fuel Pump Was Working Right.See if your Auto parts Store has only the Sending unit.if not try Dealership, Hopefully You Won't Have to Replace the Complete Unit. Hopefully this will help you. Please Let Me Know By Voting for me on the Quality of Solutions i've Given you,And Leave a Testamony if You Will. Thanks From The WYOCWBOY

good question, but they are not related, they are on 3 completely different circuits and un related in anyway, the gas guage is most likely the sending unit in the gas tank is defective, the check engine light will require a trouble code test of the system, any Kragen or Autozone can do this, it's free.

Hi, this could be cloged injectors ,have them cleaned or add a good fuel injector cleaner it should help.....good luck........