Chrysler Repair Questions? Ask a Mechanic for Answers ASAP
Hello and thank you for your question,The code C121C can be set due to a leaking EGR tube gasket which is very common . There is a lip seal on the EGR tube where it seals to the plenum that will can fail and leak . The seal will fail in the plenum causing a small vacuum leak if the seal is not installed properly. Be sure to check all EGR components when these trouble code set. I would start first with checking this.