P0093 - Fuel System Large Leak Detected (2001 model year). Always change your truck's fuel filter when this or any rail pressure codes appear.

There's a specific fuel-rail pressure test that examines the pressure at 2000-RPM and again at 3000-RPM. The difference between actual & desired fuel-rail pressure must not exceed 20-MPa, as measured with a Tech II scan tool.

If the difference between the actual & desired rail-pressure exceeds 20-MPa, the GM service test procedure winds its way through the various possibilities for a low rail pressure, such as a high fuel return rate(s) due to faulty injectors, a leaking fuel-rail pressure relief valve and concludes with either an FRP (Fuel Rail Pressure) regulator or high-pressure injection pump replacement. The test set used to measure injector fuel return rates utilizes a series of graduated cylinders that allow for a precise measurement of fuel return flow for each bank of injectors.

Jim