Q: Code P0051 shows up on my 03 Nissan Frontier SE crew cab. I have replaced all plug wires, plugs, rotor, cap, cabin filter, air fi

Oxygen sensors do not work until they reach a certain temperature. The electric heating element helps the sensor come up to temperature faster so that the engine can go into closed loop operation more quickly. P0051 says that there is no voltage at the sensor heater so the engine will take a few more moments to go into closed loop operation. You probably will not notice any symptoms other than the check engine light. Replacing the O2 sensor will often solve this problem, but if the issue is upstream, say in the wiring harness or the heater relay (another common failure) changing the sensor will not help. If you have changed the sensor and still get the code, you will have to do a point to point check of the wiring harness to see where the interruption of power is located. You can have a professional do this for you at your convenience by contacting Your Mechanic. They can send a technician to your home or office to check out your Nissan and let you know just what it;s going to take to solve your problem.