Hi, this is Bo, an auto expert on RepairPal's Car Genius team!
It sounds like your Kia Soul is having some frustrating issues with acceleration. The P0420 code points to a problem with the catalytic converter, while the P0121 code indicates a potential issue with the throttle position sensor or its circuit.
Since you’re experiencing a loss of acceleration, it could be linked to the throttle body or sensor malfunctioning. When you turn the car off and on, it temporarily resets the system, which might explain why the pedal works again for a while.
You might want to start by checking the throttle body for any dirt or debris and making sure the wiring and connections to the throttle position sensor are secure. Also, inspecting the catalytic converter and ensuring there’s no blockage could help resolve the P0420 code.
If these steps don’t solve the issue, it might be best to have a professional diagnose it further. They can check the sensor and exhaust system more thoroughly.
If you need more advice, have other questions, or need to find a certified repair shop in your area, just let me know! Call us at 877-913-1554, and we'll gladly find you a certified RepairPal shop in your area!
