Oh, that's not a good code to have. The service manual does say to check for loose terminals at the "IGP line connectors" so it means checking the IGP (Power Source) for the PCM which is Connector B, terminal number B3, a yellow/black wire at the PCM. Unfortunately, if the power feed to the PCM is OK then there are only two possibilities for that code. Either the PCM needs to be updated or it needs to be replaced.

Since you're seeing some other flickering lights it makes me think a loose connection somewhere. It looks like fuse No. 23 (7.5A) in the driver's under dash fuse box feeds that terminal at the PCM, as well as the the PGM-FI main relay, PGM-FI subrelay (LAF), the main relay fuel pump, and the electronic throttle control system relay. It also feeds the fuel injectors, the CMP sensor and the CKP sensor so there's a lot of stuff on it. It's also possible it could be a battery cable issue, too.

Hope that helps. It could be something simple, just hard to find or something complicated and expensive.

 

Thanks so much john. Does that mean unplug the PCM connector B and throw a multimete on the yellow/black wire and turn the key to run? also, your saying fuse 23 could be the culprit?

I will also cleant the battery terminals but that means loosing the code... the battery (genuine honda) was manufactured 11/11 and under the hood IS filty... like its been that many northern winters since under there was washed. I actually clean my engines, but no judgment to the previous owner as they were early and often with the maintenece.

The strange thing about this whole thing is that it was fine for probably 220 or more of the 261 mile drive home. I noticed the lights maybe 45 minutes from home... then switching to the highbeams causes the blip, and that got worse and worse every time for the last 10 miles. I had though alternator, but at idle, its exactly as it should be

 

I think I'd save unplugging the PCM for a last resort. I'd check the voltage on that fuse, maybe even change that fuse, though changing it might cause it to lose the codes...I'm not sure what power source keeps the computer memory alive.

If it were me, I'd replace that battery. It's nearly 7 years old and you said it's been sitting for a while. 12.7v means it has a surface charge on it. Put a load on the battery by turning the headlights on high beam, ignition on, HVAC on, etc. for a few minutes and see what it drops to. Regardless, I wouldn't trust it at its age anyway. I'd clean the terminals while you're there.

Not sure you can pick one up locally but a memory saver is handy for battery changes. You plug it into the data connector and plug the other end into another power source (jump pack, another car, etc.) and it will keep everything powered up while you change the battery.

 

John,

Thank you! Before I got your response, I loosened but did not disconnect the battery terminals, rotated back and forth to grind away corrosion, and retightened. I also inspected fuse 23 and swapped it with the tpms fuse for kicks. I also taped gently on the huge relay under the hood that is screwed down with a Philip’s (assuming that’s our ecm relay) and drove maybe 8 miles. I did everything that was causing the issues yesterday (headlights on with the radio ad a reading lamp, kicked high beams on and off) and there is zero issue. Engine light still on but thinking it will go off after 50 miles. Strange... I mean, awesome if it never happens again but I’ll wonder for the rest of the time I own the thing if it’s goinf to leave us hanging on a road trip or something. It was after 200+ miles of continuous driving


I found a memory saver supposedly at advance auto parts and it plugs into another car’s cigarette lighter. $22 worth a spot in my tool box. Especially given that my 2002 Lexus has auto up and down windows/sunroof/mem seats and it’s a bear to reprogram all of that.


So if I ended up getting a new ecm, it’s easy to put in but would need to be programmed. I saw a video on soldering 2 chips from the old one to the new one. I fixed or washing machine’s motherboard similarly but wouldn’t want to try it with a $100 used part that, if fails later, leaves my wife on the side of the road. Any idea how I would have it programmed to my key?


COULD this have just been gross battery terminals? And could an alternator act funny only after being warm/running for extended periods of time but be fine cool at idle?

Thank you very much

 

It's possible it could be any of those things. There is no "ECM relay," however. The code description in the factory service manual doesn't have the word relay in it. Code descriptions in generic scan tools are often hit and miss. The code is likely correct but the description isn't. Knowing exactly what sets the code would be helpful but Honda doesn't publish that. They just check the IGP line connectors and then update the PCM and if that doesn't fix it then replace the PCM.

On PCM replacement if you go used you can't swap over the maintenance minder and mileage data. If you go new then it can be transferred over. Even my Autel scan tool has the option for doing it but I've never tried it. The other issue after swapping the PCM is programming the keys. I've never done either with my scan tool.

 

Yikes. I have heard locksmiths can do the keys but by mileage data do you mean the odometer? This isn’t good. Wonder what Honda gets to do it?

I am going to clean the battery terminals and put that anti corrosion stuff on them. Perhaps if that doesn’t work it would make sense to use electronic components cleaner on the 3 ECU connectors? Also some anti corrosion spray?

Hoping for batter terminals

 

Mileage data isnt only on your odometer, but also saved in PCM..

Change your battery, come on now, it is 7y.o.. Old battery can do many things, even cause a fire.

 

Yep, change that battery.

Yeah, the vehicle won't start until the new PCM is programmed and the keys reprogrammed. I might be wrong on the odometer and the MM data. Now that you mention it, I think it's actually saved in the gauge cluster module.

 

Monday I can get a blemished understate battery for like $45. I’ll probably do that. My positive terminal won’t tighten enough. I’ll need to replace that

I cleaned the terminals. Engine light didn’t come back and lights aren’t flickering but it hasn’t been more than 15 miles or so

Can an alternator overheat or act up under long/big loads but not under normal/small ones? It reminded me of when I lost my alternator on my old Solara 80 miles form home and had to keep above 2,000 rpm or stall. Windows auto rolled down cause of jamb protection no wipers. No nav. Awful

 

Can an alternator overheat or act up under long/big loads but not under normal/small ones?

Alternator with loose mounting bolts ( bad ground connection ) can do a lot of things, including fried PCM. Check these bolts. Check the alternator itself, make sure it is not autozone alternator. Used car can be full of surprises.

 

On your positive battery terminal, that's actually not a problem with the terminal. For whatever reason the original battery in the vehicle has a larger positive terminal than the replacement batteries. Go to Advance Auto or Autozone and get a battery terminal shim. It just drops over the terminal and you tighten the cable over the top of it. It allows you to tighten down your cable properly. Almost nobody does this but pretty much every Honda needs this:

 

On your alternator question, it's possible this could happen but I wouldn't expect the symptoms you saw from it. Worst case is that the alternator stops charging but your battery voltage would still be 12.6 or more at those intermittent drop outs. It shouldn't affect the power feed. A loose terminal or corroded connection could easily drop it more than that.

 

Found the shims. They’ll be going on soon. I am not naive enough to blindly believe that this is a fluke, but I honestly think it was terminals. I haven’t replicated the issues but I’ve only driven maybe 20 miles since I bought it

 

I'd definitely replace the battery, add the shims, clean the terminals, clear the codes and drive it and see what happens. I would exhaust everything before changing a PCM.

 

That’s what I am hoping for. Batter and shims are for sure. Before I the pcm, I will take off the harnesses to it and clean them with electronics component cleaner. Then do some multimeter investigation (not my strong point) and leave the pcm for last. Really hoping and praying it was just the terminals. Before I did the pcm I would do an alternator as well


This van is just so, so, so clean if it does have a major issue it still is worth it. This thing was maintained with an open checkbook at a Honda dealer

 

Sure will check them. Would be shocked if it’s not oem... these people went to the dealer for every little thing.

Really just hoping it’s the terminals. They were nasty. Looks like the engine bay was filthy with road salt. Cleaned it. Looks new

 

If, at some point, you do decide to disconnect the PCM, Honda recommends you jump the SCS line before doing so. That means jumping the #4 and #9 pins of the DLC. Then you can safely unplug it. The PCM is still active even with the key off so jumping those pins makes sure the PCM isn't doing anything when it's unplugged.

I bet a new battery and clean terminals will fix it. PCM issues are so rare and with that thing sitting for so long it is highly doubtful it has a bad PCM. I wouldn't even replace the alternator just yet.

 

Which is SCS and DLC? Not familiar with those acronyms. And I am really really hoping so. We sold our home and are moving in with family for 6-8 months to wait out the “bubble” or buy from a family member who is upgrading, so the driveway garage situation is tight. The extent of my electrical experience is having built my own wiring harness from scratch for my 1950 with the stock diagram as a baseline. This is way above me BUT that’s an opportunity to learn.

I’ll be getting a battery today. Won’t be another Honda- shame this car is 100% honda and I’ll be changing that - but interstate will have to do

Thank you very much

 

Which is SCS and DLC? Not familiar with those acronyms.
Thank you very much

 

So it’s the obd2 thing? Thanks!


So I got a new battery. An interstate with a “blemish” so $46 for brand new with a 6 month warranty. 860cca as tested when I left. The new battery didn’t need the post shim... but the genuine Honda one I took out did. Weird

There have been no electrical gremlins since. Praying it was the corrosion on the terminals because last time it was after a couple hundred miles of continuous driving before it happened. If that’s the case again, it’s on a road trip with my bride and minions


I’ll report back

Appreciate it guys

 

Guys,

I am almost convinced it was the batter/terminal. Just will always been in the back of my mind until the van makes a 500 mile trip without a problem, because it started after 150 miles of driving. If that’s the care (I mean if it comes back after hours of driving continuously), i’ll Assume it is an overheating alternator.

This was a scary experience - amplified by the fact that I just got the car and so much is riding on it - literally.... the love of my life and 2 kids i’d die for without question. Money is also extremely tight lately and having just been through the accident, my nerves are SHOT. Anyway, I think I know why the terminals were so dirty... the previous owner bumped something with the bottom corners of the bumper.. one is just scratched, the other was pushed in (I popped it out). In doing so, it lowered the bumper and grill probably 1/8th of an inch and that allows road spray under the weatherstrip on the front edge of the hood. No big deal, I can fix it. every panel on this car is original and near perfect. the front bumper needs love. May put a temporary extra weather strip on it until I have time to remove the front bumper, repair the small crack from the dent, paint the scratches and clear the whole thing. then reassemble correctly.

thanks for all the help through this.

 

I agree with your diagnosis. PCM's rarely fail so whenever you suspect a problem with the PCM, keep looking. Replacing the battery and cleaning the terminals is the first thing to do. Then just drive it. If it happens again then get deeper. I think you're probably fixed, though.

 

Hope so! Thank you for your help through it.

 

Just in case anyone else is experiencing this issue, documenting my experience here -

2005 Odyessy EX / base model
Throwing code P0685

Issue started when I had a bad motor mount, every time I let off the throttle the car would very quickly power off and back on, radio would take a second to reset. Eventually, it stopped being that consistent, and completely randomly would happen instead. Issue eventually seemed to have went away after I replaced the front motor mount. Engine light would come and go as it pleased.

Issue came back recently and now only happens if I flip my high beams on, nothing else causes it at the moment. Inspected battery connection and ground conncetion and they seem fine - going to take off the connections, clean them, and replace the relay soon to see if the issue persists. Firestone told me my battery tested bad a year ago but it has been working fine and tested fine when I went to Autozone to get it tested, will replace the battery if the issue persists. I suspect they were trying to sell me a new battery because I keep going there for the lifetime alignments.

Will update as soon as I clean the connections and drive it a while.