2010 Honda accord EX-L 2.4 L 4 door auto trans. Intermittent crank no start. When it is running occasionally it looses all power for less than one second then comes back before the engine stalls. Currently the engine will crank but no start and has been that way for about a week. There is no spark and there is no fuel pressure. The fuel pump does not kick on when the key is first turned on. OBD II scan when the car was running showed P0685 ECM/PCM Internal circuit malfunction (Power control circuit). Currently when the scanner is hooked up OBD II scanner is unable to communicate with ECU.
we have looked everywhere for a loose connection or corrosion / bad ground. I am unable to find a good circuit diagram to trouble shoot power supply to the PCM. I am also unable to locate a main relay that would supply power to the ECM. Does an 8th gen accord have a main relay? If so where is it? I have replaced what Honda is calling a “relay unit” under the hood fuse box. I have been watching countless you tube videos trying to find a “main relay” for the 2010 accord but no luck. I have been trying to trouble shoot the working with a multi meter but I can’t find any good schematics on the 2010 Accord. I do not know for sure that the ECM is bad. Several places online state that a bad ECU is unlikely. Is that accurate? Any help is greatly appreciated!!

 

An update. Turns out after having a 3rd party (non dealer) test the ECM, it tested “bad” and non-repairable. The tech testing it said that he has a nick name for the P0685 code “The death code”. The tech also said the ECM is now junk or essentially a “paper weight” . So we are looking for a replacement from and junk yard and a way to program the immobilizer after install.

 

have you tried to repair the module alot of times faults can easily be repaired cheaply strip it down and check for a shorted cap worth ago and would save $$$$ ive done a few board level repairs to bad modules in the past

 

Threw in the towel and took it to the stealership. They found a broken wire between the ECM and the relay unit. $630. Not as bad as it could have been.