Are you sure it's a P0216? The reason I ask is because that code isn't listed in my service manual.
There is a P0261 listed which is a #1 injector circuit low code. If it's a P0261, that means the injector circuit is being pulled low or short to ground.
Possible causes could be a shorted #1 injector, the wiring to #1 injector chaffed and shorting to ground or possibly an internal fault in the ECU.
Since ECU's are very expensive, I would start with testing the injector and wiring first.
To test the injector you can measure the resistance with an ohmn meter and compare it to the other two injectors or the specs in the service manual. It is possible for the resistance to check out OK cold, but once the injector warms up to operating temp it could fail.
In this case you could swap the #1 injector to another cylinder. Then clear the code and run the engine to see if it resets the same code or if it follows the injector to the other cylinder and sets a different code.