P0204

Injector circuit/open, cylinder 4.

The computer detected an electrical problem in the control circuit for injector 4. The code does not prove that the injector itself is faulty.

What should be checked

An interruption, abnormal resistance or poor connection may prevent the module from controlling the injector.

In plain language: The electrical current may not be coming correctly to the indicated injector.

How to check it: Inspect visible damage and check feed, continuity and control only with the correct diagram.
Before correcting it: No terminal bridges or voltage applications without knowing the circuit. The correction is decided only after locating and confirming the defect.
Related components: This path may involve the indicated injector connector, wiring, power supply, ground, or terminals. None has been confirmed.
When to stop: Go to a professional to measure the circuit if you don't have the right diagram and equipment.

The controlled component or the electronic stage that activates it may not respond as expected by the module.

In plain language: The injector or whoever activates it may not be responding, but the code doesn't say which one.

How to check it: Follow the electrical and functional test of the manufacturer before removing any fuel components.
Before correcting it: Don't change the injector or the module based on the code alone. The correction is decided only after locating and confirming the defect.
Related components: This path may involve the indicated injector or its driver stage inside the control module. Neither has been confirmed.
When to stop: Pressurized fuel and module testing shall be kept in trained hands.

Choose the make and open its official portal to find the manual, diagrams, cylinder arrangement, and bulletins for the exact vehicle.

Availability, registration, and cost depend on the manufacturer. The link does not grant permission to copy the manual.

Understand which emissions-related service information manufacturers must make available for purchase.

Explains regulated access in the United States; it does not contain the vehicle-specific diagram or make the manual free.

Audi A3 Quick Reference Specification Book — Audi of America / archivo NHTSA. It supports the punctual definition of the code; It does not identify a cause, a part or a repair.
Frequently Asked Questions About On-Board Diagnostics — U.S. Environmental Protection Agency. Supports the safety difference between a fixed breakdown lamp and a flashing lamp; It doesn't diagnose the cause.