I believe it means at least one of your Oxygen (O2) sensors has gone bad. A 1999 Camry has three such sensors (on at least the V6 engine). The car will still run basically fine, but a couple of things might happen: 1) you might notice lower gas mileage and/or engine performance and 2) you could potentially shorten the life of the catalytic converter. Also, if you live in a state that requires a regular smog (emission) check, the car will most likely not pass.
The computer has detected a fault with one of the electronic components and is warning you to run a diagnostic test.
The 2013 Toyota Camry has an inline 4 engine.
The 2004 Toyota Camry has an inline 4 engine.
The 2014 Toyota Camry has an inline 4 engine.
The 2010 Toyota Camry has an inline 4 engine.
The 2009 Toyota Camry has an inline 4 engine.
The 2011 Toyota Camry has an inline 4 engine.
The 2008 Toyota Camry has an inline 4 engine.
The 2005 Toyota Camry has an inline 4 engine.
The 2006 Toyota Camry has an inline 4 engine.
The 2001 Toyota Camry has an inline 4 engine.
The 2012 Toyota Camry has an inline 4 engine.