what does the code Po420 on a Toyota Prius after a $580.00 tune up mean?

Question

Hello,
My engine light came on I took it to Auto zone to be tested. The codes came up: Cylider 1,3,4, all the same code which are 661,662,663,664. Took it to the dealers to be fixed and gave them these codes. I did copy them for my records. When I picked the car up after the tune up which was MOC1121 Fuel Injection,MOC1961 Fuel Induction, MOC1161 Cooling System, 00272SLLC2,MOC1031 Transmission C, 00289ATFWS,9008091184 Spark plugs and #580.00 dollrs later I was driving home twenty mins from the dealers the check engine light came on again. The dealer was closed so I went to Auto Zone and Advance Auto to have the check engine light checked out. Both places came up with the same codes which are:C1241-Low battery voltage or high, C1249 Open Circut in stop light switch, and Po420 Catalyst Stem Eff below threshold Bank 1. The dealer still has the car and said to me that they have to check with the reps @ the system we use to clean out fuel systems. What does that exactly mean? Thank you April

Answer 1

What octane fuel are you using? if you are using low octane fuel that could cause this issue. A fuel system cleaner and 91 octane fuel from Shell is a good first step for P0420.

C1249 is related to the bake light, either there is a bad bulb or the brake light switch (is behind the brake pedal) is bad.

C1241 (low battery positive voltage or abnormally high battery positive voltage) is set off by a voltage drop to the ABS relays. Its possible C1241 caused this issue, I would check to see if the bulbs are working and if they don't come on when pressing the brake the brake switch might be bad.