P0204: Injector Circuit Malfunction Cylinder 4

What P0204 tells you, and what it does not

The computer commands the injector for cylinder 4 to open for a specific pulse width and checks the driver circuit for the matching electrical response. This code sets when that specific injector's circuit does not behave as commanded, which the computer can isolate to cylinder 4 because each injector has its own driver line. It points to a wiring, connector or injector problem on that one cylinder rather than a shared fault.

The code sits in the fuel injector circuit area and is reported by the comprehensive component monitor. It names the circuit or the condition where the computer saw a reading outside its expected range. It does not name a failed part, and several genuinely different faults set this same code, which is the whole reason the causes below are ordered rather than listed.

What people usually notice

• Misfire on one cylinder
• Rough idle
• Flashing or steady check engine light
• Loss of power
• Uneven exhaust note

What causes P0204?

The causes below are ordered by how often they turn out to be the answer, cheapest and most common first. That order matters more than the list itself: the expensive component named in the code text is very rarely the first thing to replace, and working down from the top is what stops a fuel injector circuit fault becoming an expensive guess.

Corroded or unplugged connector at that injector is the one to rule out before anything else. That connector is the easiest and cheapest thing to inspect first.

Working out which cause it is

Start with freeze frame. Engine RPM and load at the fault show whether the fault only shows up under acceleration or boost. That snapshot is taken at the instant the code set, and it is the single most useful piece of evidence you have, which is also why clearing the code before reading it is such a costly habit.

This code is diagnosed by watching values change rather than by reading the number again, so the tool has to stream live data and hold freeze frame. Live injector pulse width or a fuel trim comparison between cylinders confirms which side of the circuit failed.

The order worth working in

• 1. Corroded or unplugged connector at that injector: That connector is the easiest and cheapest thing to inspect first.
• 2. Chafed wiring between the computer and that injector: A wire that rubs on a bracket or valve cover can wear through with age.
• 3. Failed injector solenoid on that cylinder: An injector coil can fail internally after years of heat cycling.
• 4. Carbon buildup fouling that injector's spray pattern: A partially clogged injector can draw abnormal current and trip the circuit check.
• 5. Damaged pin or terminal at the computer connector for that circuit: Less common, but a bent or corroded pin at the computer produces the same symptom as a wiring fault.

What P0204 means for driving the car

Short trips are okay, but a dead injector on one cylinder causes a genuine misfire that can damage the catalytic converter if driven far under load.

This is a severity 3 of 4 code, which means continuing to drive normally risks damage that costs considerably more than the repair in front of you. Treat the lamp as an instruction rather than a notification.

What does it cost to ignore P0204?

Running one cylinder with a bad injector circuit means that cylinder is either flooding with fuel or running dry, and either way raw fuel or unburned air reaches the catalytic converter and shortens its life.

There is also the diagnostic cost of waiting. Freeze frame data, pending code history and the readiness monitor state all describe the fault as it was when it set, and all of it is lost the moment somebody clears the code to make the lamp go out.