2000 GMC Sonoma P0200 and P0304 Codes: Diagnosis and Injector Overfueling Concern
My 2000 GMC Sonoma has reached 201,000 miles and is currently showing fault codes P0200 and P0304. I've confirmed spark delivery to all cylinders, and the #4 spark plug is wet with fuel while all others are dry and normal. The engine runs roughly, feeling like it's operating on only three cylinders. I tested the resistance of injectors 3 and 4 using a multimeter, both reading between 2.4 and 2.6 ohms — within acceptable range. Given this, I'm wondering if injector #4 could still be overfueling despite passing the resistance test. Has anyone else experienced these two codes on a 2000 GMC Sonoma? Any insights into possible root causes or diagnostic steps would be greatly appreciated. Thanks for your time and advice, Steve.
This sounds like a wiring issue, with injector #4 being the most likely culprit. Try unplugging the #4 injector and perform a KOEO (Key On, Engine Off) test. With the engine off, one wire should show 12V — typically the common power wire. Check if the control wire is grounded or has voltage; verify continuity between the injector and PCM using an ohmmeter. This will help isolate whether the issue lies in wiring or a faulty injector. GTG.