Home › Forums › Stay Dirty Lounge › Service and Repair Questions Answered Here › ’04 Honda Element – code p0721 after engine swap › ’04 Honda Element – code p0721 after engine swap October 16, 2019 at 8:12 pm #895103 DParticipant This solved my problem!!!!…a dumb mistake. Every honda I have ever messed with the plugs would only plug into the correct sensor or plug in. This element has been a whole new beast for me. I am used to the obd1 Acura integra and honda civics.