P0204 Code: Injector Circuit/Open - Cylinder 4

Quick answer

• What it means: The Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an electrical malfunction, specifically an open circuit, in the fuel injector circuit for Cylinder 4.
• Severity: Moderate to high. While you can usually drive a short distance, driving with this code for an extended period can cause severe damage to your catalytic converter and engine.
• Most common cause: A failed or clogged fuel injector on Cylinder 4, or a damaged electrical connector/wiring leading to that injector.

What the P0204 code means

The official OBD-II definition of P0204 is "Injector Circuit/Open - Cylinder 4."

In plain English, this means your vehicle's main computer (the PCM) is having trouble communicating with or controlling the fuel injector responsible for spraying fuel into the fourth cylinder of your engine.

Modern fuel injectors are essentially electromagnetic valves. The PCM sends a precise electrical pulse to the injector, which opens the valve to deliver a metered amount of atomized fuel into the intake manifold or directly into the combustion chamber. The PCM monitors the electrical resistance and voltage of this circuit. If the voltage drops outside of the expected parameters or if the circuit loses continuity completely (an "open" circuit), the PCM triggers the P0204 code and illuminates your Check Engine Light.

Common symptoms

Because cylinder 4 is essentially being starved of fuel, the symptoms are usually very noticeable. You will likely experience:

• Illuminated Check Engine Light (CEL): Often flashing, which indicates an active, catalyst-damaging misfire.
• Rough idle and engine vibration: The engine will feel unbalanced because one cylinder is not contributing power.
• Engine misfires: You will likely feel a hesitation or jerking motion, especially under acceleration.
• Lack of power: The vehicle will feel sluggish and unresponsive.
• Poor fuel economy: The engine computer may alter fuel trims in other cylinders to compensate, resulting in wasted fuel.
• Stalling: The vehicle may stall when coming to a stop.

Common causes

Ranked from most likely to least likely, the common causes for a P0204 code include:

1. Faulty Fuel Injector (Cylinder 4): The internal coil of the fuel injector can break down over time, creating an open circuit internally.
2. Damaged Wiring or Connector: The wiring harness routed to the cylinder 4 injector is exposed to extreme engine heat and vibration. Brittle wires, chafed insulation, or a loose, corroded connector are very common.
3. Open Circuit in the Wiring Harness: A break in the wire anywhere between the PCM and the fuel injector.
4. Clogged Fuel Injector: While less likely to cause a circuit code than an electrical failure, a severely clogged injector might draw incorrect voltage/current, sometimes triggering a circuit code.
5. Failing PCM: Extremely rare, but the internal driver inside the PCM that controls the cylinder 4 injector can burn out.

How a technician diagnoses it

As an ASE-certified master technician, diagnosing a P0204 involves systematically testing the electrical circuit and the injector itself. Here is the process:

1. Scan and verify codes: We connect a professional-grade scan tool to read the DTCs and review freeze-frame data to see the exact engine conditions (RPM, engine load, temperature) when the code set. We also check for related misfire codes (like P0304).
2. Visual inspection: We closely inspect the wiring harness and the electrical connector at the cylinder 4 injector. We look for melted wires, rodent damage, or a connector that isn't fully seated.
3. Noid light test: We disconnect the electrical connector from the cylinder 4 injector and plug in a Noid light (a specialized test light). We then crank the engine. If the Noid light flashes steadily, the PCM and wiring are sending the correct signal, meaning the injector itself is internally faulty. If it doesn't flash, the problem is in the wiring or the PCM.
4. Injector resistance test: Using a digital multimeter (DMM), we measure the internal resistance (Ohms) across the two pins of the cylinder 4 fuel injector. A healthy injector usually reads between 10 to 18 ohms (depending on the manufacturer). If it reads infinite resistance (OL) or is significantly out of spec, the injector has failed and must be replaced.
5. Circuit continuity test: If the Noid light didn't flash, we use the DMM to check the wiring from the injector connector back to the PCM. We check for a 12-volt supply on the power side and test the ground pulse circuit for continuity to the PCM.
6. PCM driver test: If the wiring is perfectly intact but the PCM is not providing a ground pulse to the injector, we suspect a failed injector driver inside the PCM.

Typical repair cost

The cost to fix a P0204 code varies based on the root cause and the make/model of the vehicle. Some engines (like certain V6 or V8 transverse setups) require removing the intake manifold to access cylinder 4, which increases labor costs.

• Fuel Injector Replacement: $150 – $400+ (Parts: $50–$150 | Labor: $100–$250)
• Wiring or Connector Repair: $100 – $200 (Parts: $10–$30 | Labor: $90–$170)
• Intake Manifold Gasket replacement (if manifold removal is required for access): Adds $100 – $250 to the labor total.
• PCM Replacement and Programming (Rare): $500 – $1,200

Can I keep driving with this code?

No, it is highly discouraged. While the vehicle might start and move, you should not drive it any further than a safe spot to pull over, or a short limp to a nearby repair shop.

Driving with a dead cylinder pumps unburned oxygen into the exhaust system. This can confuse the oxygen sensors, causing the engine to dump excess fuel into the other cylinders. Furthermore, if the injector is stuck open (less common for an "open circuit" code but possible in some electrical failures), raw fuel will dump directly into the exhaust, which can melt your catalytic converter in a matter of miles. A $200 injector repair can easily turn into a $1,500 catalytic converter replacement.

Related codes

You will frequently see these codes accompanied by P0204:

• P0304: Cylinder 4 Misfire Detected (Very common companion code).
• P0201, P0202, P0203, etc.: Injector Circuit/Open codes for other cylinders.
• P0269: Cylinder 4 Contribution/Balance.
• P0420: Catalyst System Efficiency Below Threshold (Can trigger if raw fuel damages the converter).

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