Two problems related to engine have been reported for the 2003 Toyota Prius. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2003 Toyota Prius based on all problems reported for the 2003 Prius.
Warning light comes on and manual says do not operate vehicle, park immediately. This happened on my 2003 Toyota Prius in December. Fortunately the dealer was open and when reported said it was not a big deal, the care was drivable and should be brought in for service. In service found master warning light codes p0300, 301, 302, 303, 304, -3191, p33101, c1202 then noted "found warranty enhancement to clean throttle body (eg9016. 5 01. 99). Was never notified of this issue and was parked in dangerous location while attempting to ascertain what steps to take in light of the "do not operate vehicle" warning in the manual. Same situation arose in our 2002 Prius this date and awaiting results of dealer's analysis (although when the light went out they said we could just as easily cancel the service appointment). In both cases service departments seemed familiar with problem (and my service advisor referred to it as a "silent recall". ).
2003 Toyota Prius -- in cold weather the cars computer does not act properly and will shut down the engine.