P0204 OBD2 Code Guide
P0204 is a powertrain diagnostic trouble code. Use this hub to understand the plain meaning, the first checks to run, and which vehicle-specific guides may be more useful before replacing parts.
Injector Circuit Malfunction - Cylinder 4
Code P0204 indicates that the Powertrain Control Module (PCM) has detected an electrical malfunction within the fuel injector circuit for cylinder #4. This means the PCM is not seeing the expected resistance or voltage drop across the injector circuit during its operation. This could be due to an open circuit, a short to ground, a short to voltage, or excessively high/low resistance within the injector coil itself or its wiring. Symptoms often include a noticeable engine misfire, rough idle, reduced engine power, increased fuel consumption, and the illumination of the Check Engine Light.
Code verification standard
P0204 is published with SAE J2012 / ISO 15031-6 code structure plus OBD2 P0204 diagnostic context.
First checks
- - Read all stored and pending codes before clearing anything.
- - Save freeze-frame data so you know speed, load and temperature when the code set.
- - Inspect wiring, connectors, fuses, hoses and obvious leaks tied to the named system.
- - Compare live data against realistic values before buying sensors or modules.
- - Clear the code only after repair and complete a drive cycle to confirm it does not return.
P0204 diagnostic path
- 1Visual Inspection: Carefully inspect the fuel injector #4 connector and wiring harness for any signs of damage, corrosion, fraying, or loose connections. Ensure the connector is fully seated. Check for any signs of rodent damage to the wiring.
- 2Injector Resistance Test: Disconnect the electrical connector from injector #4. Using a digital multimeter (DMM) set to ohms, measure the resistance across the two terminals of the injector itself. Compare this reading to the manufacturer's specifications (typically 10-18 ohms). An open circuit (infinite resistance) or a short circuit (near zero resistance) indicates an internal injector fault.
- 3Circuit Integrity Test (Power & Ground): With the injector connector disconnected, use a DMM to check for battery voltage at one terminal of the injector harness connector (key on, engine off). Then, use a noid light or an oscilloscope connected to the other terminal and ground while cranking the engine. The noid light should flash, or the oscilloscope should show a clear pulse, indicating the PCM is providing the ground signal. If no voltage or no pulse, further wiring or PCM diagnosis is needed.
- 4Wiring Continuity Test: If the injector resistance is within spec and the power/ground signals are suspect, disconnect the PCM connector and the injector #4 connector. Use a DMM to check for continuity between the injector #4 harness connector terminals and the corresponding PCM pins. Also, check for shorts to ground or shorts to voltage in both wires.
Verify before repair
- - Repair or replace damaged wiring or a corroded/loose electrical connector for cylinder #4 fuel injector.
- - Replace the faulty fuel injector for cylinder #4 if its internal resistance is out of specification.
- - Diagnose and repair an open or short circuit in the wiring harness leading to the injector from the PCM.
- - In rare cases, replace the Powertrain Control Module (PCM) if the internal injector driver circuit for cylinder #4 is confirmed to be faulty after all other possibilities have been ruled out.
Vehicle-specific pages to check next
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