Q: 2004 Nissan Titan running lean any suggestions

The causes of lean operation, such as if you have diagnostic trouble code P0171 are easiest to pinpoint by looking at the secondary firing patterns on all cylinders. That will confirm if the too lean condition, that has caused a code to set, affects all or just a few cylinders, and in which bank of the engine. If not all cylinders are affected, test for defective individual fuel injectors. However, if all cylinders are affected, you would test, in turn: the fuel pressure regulator, fuel pump pressure, check for a clogged fuel filter, vacuum leak, faulty oxygen sensor(s) and faulty mass air flow sensor. Rarely, the cause will be a faulty powertrain control module. If you want these steps performed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a check engine light diagnostic - lean operation and the responding certified mechanic will get this resolved for you promptly. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.