Q: Check Engine Light on code P3400 showing

Hello. This particular code indicates a performance issue with the cylinder deactivation system on bank 1. If you believe that all of the recent repairs are holding, then you may want to turn your attention the the solenoid and sensor of that deactivation system. To better understand what is causing the code, know that the PCM will deactivate cylinders to conserve fuel if the load is light on the engine. This is all controlled electronically with your engine input sensors.

If the engine is driving normally, it’s very likely an electrical issue. There may be an actual issue with the solenoids that control the flow of oil to those valves. There also may be an issue with the wiring to these solenoids. You can perform a visual inspection of these wires and terminals making sure they are clean, dry, and tight.