Today on the freeway going around 50mph I took my foot off the gas quickly to slow down for traffic (not braking though) and noticed the red 12v Battery light flashed for split second then went out, no other warning lights were on. Ten minutes later I did it again and the red 12v battery light came on for about five seconds then went out. Then Five or so minutes after that the CEL light came on (but not the IMA). This whole time the car ran fine totally normal. When I got to work I plugged my obdii scanner in and in addition to the usual P1600/P1433 codes there was a new one that said:
P1670 RCSD Signal circuit malfunction
I've been searching online and can't find a description of the P1670 for Hondas OR what "RCSD Signal circuit malfunction" is. Help!

I have a 2004 HCH A/T with 250k (rebuilt trans at 180K) and 6mos old 12v battery and I average 41-42mpg. The CEL & IMA light have been on (when i don't clear them) for a year now with the same P1600/P1433 codes always but IMA still works ok. I installed a Hybrid Automotive grid charger and went through the whole charge/discharge procedure and it didn't help anything, I'm sure my pack is too far gone to save.

 

P1433 is essentially the worst battery error you can get.

Once a pack gets bad enough, it starts to trigger other issues. One of them is sporadic DC-DC converter operation.

I've never heard of a P1670. Are you 100% sure it's not a P1570?

A P1570 is nearly a guarantee that you have a full-on cell failure, and it can definitely cause intermittent 12V charging issues.

 

Had to look through most of the service manual to find it, and it came up with a slightly different number.

In the Honda service manual I have it lists P1679 (not 1670) as RSCD Signal Circuit Malfunction in the Fuel and Emissions systems section, That links to a description in the PGM-FI system section. PGM-FI apparently includes all the motor related sensors like Camshaft position, brake booster pressure, engine coolant , MAP and so forth. The description goes on for pages describing tests on ECM connector E, TCM connector C, and MCM connector A. 26 steps in the check list. Near the end it suggests either upgrade the ECM, replace the ECM, or replace the MCM. Near the beginning it suggests that this could be a loose or dirty connection for one of those connectors.

I still don't know what "RSCD" is. It seems to be on ECM Connector E in position 27 (or maybe 17, the drawing is poor) and is a blue and white wire. There is also RSCDC on TCM connector C which is a black/orange wire.