Reverse polarity

[Rubywillow]

I have accidentally reverse polarity the car. Initially the car went completely dead. I have changed the main fuse and I now have electronics. However, I cannot start the car. It says check engine on the dash.
Checked all fuses and they are not the cause. Has anyone experienced this before?

 

[Ecmbuster]

No make, model, year or trim level indicated.
The best primary solution is to have a scan tool that is network capable, gather the recorded faults.
The scan will indicate what controller recorded the faults and which controllers are or are not communicating.
With a fuse panel layout, test the fuses for open (burned) circuits. A test light will be an aid.

https://www.amazon.ca/OctagonStar-Circuit-Systems-Continuity-Voltage/dp/B01HUZPTPS

Some circuits are also active with the key in the ON position, others do no require the key in the ON position.

 

[Rubywillow]

Hello, thank you for your reply vehicle is a Subaru XV 2018. I have checked all the fuses and it is not the problem. Thank for your advice.

 

[Ecmbuster]

Both fuse panels?

Fuse Box Diagram Subaru Crosstrek / XV (2018, 2019-...)

Fuse box diagram (location and assignment of electrical fuses) for Subaru Crosstrek (XV) (2018, 2019...)

fuse-box.info

Some times and not all the time, controller assume the role of SOS (Stuck On Stupid) for many reasons.
Try this with the key removed:
Disconnect both battery cables and attach a wire between both cable only.
This will drain capacitance learned values. Leave in that condition for an hour.
Reconnect both cables but be aware anything that was setup before (radio, clock,seats memory) will need to be reset again.
If the instrument lights are ON and still no start, make sure the transmission is in the P or N position and try again.
If the no start condition persists, the battery should still have 12+ Volts.
This is when a proper scan tool is used to access the network for related faults and or non communications within the network.
Why was the battery reverse connected?