2004 Kia Rio P0271 and P0304 Trouble Codes: Diagnosis and Solutions
I own a 2004 Kia Rio with 155,000 miles. I'm experiencing intermittent engine performance issues indicated by OBD-II trouble codes P0271 and P0304. I've already checked the fuel injector (replaced with a new one), confirmed that the connector is not corroded, and inspected the wiring harness—no visible damage has been found. The problem occurs intermittently, especially during idle or while driving: smooth idle turns rough, and acceleration becomes sluggish or stumbles. I'm looking for guidance on the next troubleshooting steps to identify the root cause of these codes. Any insights would be greatly appreciated. Steve
The P0271 code indicates a circuit issue with the #4 fuel injector, while P0304 points to a misfire in cylinder #4. A noid light is highly recommended for diagnosing this issue. To troubleshoot: disconnect the #4 injector (KOEO condition). Check if the 12V power wire is receiving voltage and verify that the signal wire is properly connected to the PCM—look for an open circuit or grounding issue on the signal wire. This test helps isolate whether the problem lies in the injector itself or its wiring. For more details, refer to: http://www.obd-codes.com/p0271