P0204

Code P0204 indicates the engine control module (ECM) has detected an electrical malfunction in the fuel injector circuit for cylinder 4. The ECM monitors each injector circuit for proper resistance and current flow, and when cylinder 4's readings deviate from the expected parameters, this diagnostic trouble code is set.

The symptoms are similar to other single-cylinder injector faults: rough idle, engine misfires, reduced power, and poor fuel economy. On a four-cylinder engine, losing one cylinder means 25% of your power is gone, which will be very noticeable. On larger engines like a V6 or V8, the effect may be somewhat less dramatic but still clearly felt as engine roughness and vibration.

Start diagnosis by checking the cylinder 4 injector connector — unplug it, inspect for corroded or damaged pins, and ensure it clicks firmly when reconnected. Use a noid light to verify the ECM is sending pulses to the injector. If pulses are present, the injector itself is likely faulty. The swap test (moving the injector to another cylinder) is the quickest way to confirm. Replacement injectors for most vehicles cost $50 to $150 each, and the swap typically takes 30 minutes to an hour for accessible cylinders.

Severity

Symptoms

• •Check Engine light is on
• •Engine runs rough and misfires
• •Noticeable power loss
• •Increased fuel consumption
• •Engine shaking or vibration
• •Difficulty maintaining steady idle

Likely Causes

Estimated Cost

Common Fixes

1. Replace the cylinder 4 fuel injector
2. Repair or replace damaged injector wiring harness
3. Clean or replace corroded injector connector
4. Swap injectors between cylinders to confirm the fault

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