We use the locally generated photovoltage in carbon nanotubes to image potential modulations produced by defects. The correlation with spatially resolved spectroscopy of the disorder-enhanced Raman band allows us to locate the defects and to determine their effect on band bending. The defects produce local potential maxima, which are consistent with trapped electrons near the tube. An offset photovoltage is generated when the laser populates metastable traps in the oxide. Previously uncharged defects can thus be imaged. To demonstrate the versatility of the technique, we show that tube-tube junction at the base of nanotube loops can be electronically characterized.