Four problems related to wiring have been reported for the 2004 Toyota Prius. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Toyota Prius based on all problems reported for the 2004 Prius.
I purchased this vehicle in December 2012. Ever since I have had this Prius, I have had issues with the front drivers side headlight turning off randomly. Whenever I turn the car on, both headlights are always on, but while driving, the drivers side headlight turns off. I took it to carfix in garner, nc and they thought that it could be the headlight, so they recommended changing it. I ended up having it changed by a family friend because it was cheaper to do it that way. The headlight was still giving me problems after being changed, so I took it to the leith Toyota dealership in raleigh, nc and they said that the headlight that I purchased from autozone was not the correct type of headlight, so they changed it again. Even after they changed it, the headlight was still going on and off randomly. I took it back to the Toyota dealership today and they said that it sounds like some kind of wiring issue. I have done some research on the issue and have seen recalls for 2005-2009 Prius' for the same issues, but since mine is a 2004 it does not fall into the recall category. I believe that it should based on my issue compared to that as well as the number of other complaints on the internet and blogs that I have found.
Water intrusion caused corrosion of the main engine wiring harness which caused a fault in the auxiliary 12v battery and has made the vehicle undriveable. Toyota cannot determine the source or cause of the water intrusion even though I have brought in the vehicle for routine maintenance since I purchased it and I have complained about a problem which is related to the auxiliary 12v battery several times in the past. This seems to be a flaw in the 2004 Prius design.
Have a 2004 Toyota Prius. Less than 40,000 miles on the car. Was driving on the freeway and it suddenly died for no reason. Toyota dealer said it was a computer malfunction and could not guarentee it would not happen again. Very upset about this as it is a new car I paid a lot of money for.
Dt; last summer was driving down highway at about 45-50 mph and one of the engines went out, and the car decelerated and finally stalled out. Parked by roadside ,and had to be towed to dealership. Serviceman did a computer correction, but did not record this because it happened at night. Again about 2 months ago the engine went out, car slowed, and would not restart. Had to be towed to dealership. The car was returned without explanation. Afraid this may happen again.