I'm helping a friend repair a 2007 Civic Hybrid. We recently replaced the hybrid battery with one from GreenTec auto; however the vehicle still has a code U1221 and the 12v battery will not charge. I'm using a BlueDriver scanner to read the codes, so I'm not sure if it is fully compatible with the IMA system. I also replaced the 12v battery with a brand new one. I've done quite a bit of searching but don't seem to find many people with a U1221 code. Most have codes that start with a P. The hybrid assist and charge seem to be working, but the car dies after driving it a short while because the 12V won't charge. I checked the fuses in the little box of the battery and that the connection was tight. I'm looking for any troubleshooting tips or recommendation on a good code reader that works well with the IMA system.

 

Code reader is probably working fine.

U1221 - BCM module lost communication with DC-DC Converter.

Pretty extensive diagnostics troubleshooting U1221.

Check #3 fuse in under-dash fuse box, 10A. Could be wiring issue or failed DC-DC converter.

https://www.ebay.com/itm/OEM-Digital...9/282338335433

 

Thanks for the assistance. I checked the #3, but it's good. Sounds like I have some work ahead of me.

 

I am having the same issue, did you ever find a solution?