One problem related to o2 sensor has been reported for the 2004 Toyota 4Runner. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2004 Toyota 4Runner based on all problems reported for the 2004 4Runner.
While driving, the cel (check engine light) came on and the vsc trac and vsc off lights came on as well. Apparently Toyota disables vsc when the cel is triggered. In my case, the 2 times it has occurred has been due to emissions related failures (1st time the cat failed, 2nd time one of the O2 sensors failed). In the 1st case, I immediately took the vehicle to the dealership as I was approaching the end of the emissions warranty. They made the repairs and cleared all the codes so wasn't aware that the vsc system was actually disabled. The 2nd time (O2 failure) I replaced the failed O2 sensor, the cel has cleared, however the vsc lights are still on and vsc is disabled. I have serious concerns that Toyota disables key safety systems due to emissions related failures especially given the inherent stability problems with SUV's. If I'm on a trip with my family and an O2 sensor fails, or a catalytic converter fails, or the gas cap fails, key safety systems that help keep my family and I safe should not be disabled! I think this deserves an investigation.