07ARDI

My daughter was driving along, normal weather, normal driving. Car electronics dropped to zero and said"goodbye" like she shut the car off. It only happened momentarily. I went to see what happened and found that her Positive battery cable was pretty loose. I though ahhh that must have been causing the issue. A few days later, it happened again and set the code P0685 as well as a check emissions light.
I looked for any loose or damaged wires, checked battery cables and attachments, checked and pushed on all fuses and relays jiggled all wiring looms and wires that I could get to. wiggled and checked ground straps. No obvious reaction or changes to the car. Drove fine for a day or two then did it again. I noticed that if it is idling I can almost make it die by flipping on the headlights.(putting excess electrical load on but not always)
Code was PO685 said ECM/PCM power relay control circuit /open
Battery is about 6 months old. Shows 12.6 volts sitting in the morning with nothing running.
When running I noticed that it started at 14.01 then dropped as it ran at idle then would jump around and then settled down to a low of 12.9. (Not sure if that has anything to do with the Decoupler on the front of the alternator)
I also used my cheap scanner to do an alternator test which had me run the car with headlights on at 2000rpm. After the test it said alternator was good and within specs.14.3volts
Is there a relay that is possibly suspect? Is there an ELD on these? I have seen people in the older Honda community mentioning a problem with that.
Other than that. I think I might be looking at trying to find a ECM/PCM whatever Acura calls it. I assume it would need to be flashed or programmed by a dealer if I swap one in.
ANY HELP WOULD BE APPRECIATED!!!!! Thank you.

ATTACHED is a video at :35 seconds you can see that the power suddenly drops out and then comes back on.

Tomtwtwtw

Unfortunately while the code points to the PCM/ECM, really it could mean some sort of short or disconnect somewhere in the electrical system. Does the car start strong (fast crank/fast fire up)? Any other electronics that cause the blips (radio, seat heaters, power windows, etc)?

07ARDI

Seems to crank and start at normal speed. Not like if the battery were low.
It seems like there are some clicks, pops coming from the radio. The DVD Nav unit hasn't been able to find the disk since we have owned it. I have cleaned the disk and the laser on the DVD drive but it only finds it on rare occasions. Otherwise it doesn't seem to shut down when I suddenly start, the radio, power windows seat heaters or other electronics. I did however wonder if it had something to do with the fans or AC clutch or something clicking on the associated relay. But haven't seen a real pattern.

Tomtwtwtw

Hard to say then...I did have a similar issue some years back, but it ended up that my positive terminal had corroded so bad to the point where it could no longer maintain a solid connection to the battery. This was not long after I got the car and didn't realize that the previous owner must not have ever checked the terminals. Replaced the positive cable and all was good. But, in your video it all seems pretty clean, at least from what I can see.

07ARDI

So I just took off my battery terminals and gave them a very thorough clean, Took the ground strap off that is attached to the bell housing/trans and cleaned that up real good as well. Re- attached everything. Seemed like maybe it was different ran in the driveway for about 20 minutes fine, drove around without issues. came back, took it out again and it started doing it again. Pulled into the driveway, put it in park flicked the headlights on and died. Something weird about when it pulls power for accessories. When it did it when we were driving it was not a result of flipping on the headlights. I will keep looking and trying and let you all know if I figure anything out. In the meantime any suggestions Please fire away. Thanks

07ARDI

Well sad and frustrated to say I have not got this figured out. Just to make sure I pulled the alternator out and swapped it. No change. Pulled the entire center entertainment section apart and looked at all connections and grounds in there. Nothing of particular concern. Left the radio and seat heaters disconnected as well as the Bluetooth unit just to make sure one of those items weren't causing the issue. I see a lot of chatter in Honda and others regarding the ELD (electronic load detector) In many cases it looks like a replaceable part, but with the 1st gen RDX I am not seeing it in the fuse box like it is in the others. Any body have any thoughts or experience with that.
I feel like at this point I need to probably swap the ECU, but I am not sure if I do that if it will run in order to get down to the dealer to have them initialize it or reconfigure it to work with my car VIN.

Any HELP is appreciated.

deepa1600

Check this video

07ARDI

THANK YOU DEEPA. This was the problem I think. She is driving again today. So fingers crossed. I think that was the fix. You guys are GREAT

07ARDI

crud..... Spoke to soon. drove it this morning and it is back to the same thing. I will keep looking and let you kno if I find a different problem or solution.
.

07ARDI

I wanted to circle back on this and give my experience.I got a wiring diagram and traced every ground I could find in the car. Cleaned and re mounted all of them. Then replaced the ground from the battery to the chassis where it mounts. I then used my scanner and cleared all of my codes. So far I think I have this intermittent power loss taken care of. Unfortunately, there is still a very strange audible electric pop that occurs at startup. I haven't heard it, but it also happens from time to time while driving( this is according to my daughter. I am going to remove the amp and DVD nav unit again and try without them connected for awhile and see if it continues. I don't think it was doing that when the amp was out when testing before.

JCash23

I’ve had a few issues prior to last nights events when my car voltage dropped to 12.3, the car started jerking without acceleration and accessories all flickered before the car could die I was able to pull over and park. Prior to last night events I’ve had issues with low voltage and multiple dead batteries, led to Po685 code, check engine & check emission system lights coming on. I’m having another new refurbished alternator put in as well as another brand new battery, three days ago I replaced a non existent ground cable that was so far gone you couldn’t tell one was ever there to begin with, I’ve changed the AC relay to the upgraded one. Prior to last night my alternator tested bad and my battery was to hot to be tested on two separate occasions prior to finding and replacing the ground wire.

Do you think I should replace those three relay in the video? Should I replace the ECM or should I retrace the grounds,clean reinstall all wires and cables? I’ve felt alot of heat radiating from the engine area into my interior cabin but havnt been able to find a solution or a cause of where or what’s causing the heat issue since the Ac / Heat unit is off. I did also notice that my voltage drops as soon as I turned AC on which led me to change the relay after I installed the new ground cable, although the ground cable has given me higher normal voltages readings of 14.1, 14.2 it drops significantly to 12.1 with the Use of the AC even after I replaced the ac relay. I’m Hoping with the new refurbished alternator and the brand new battery install that the new ground cable and upgraded AC relay is going to fix all my problems…. If you have anything to add I’d be appreciative of your knowledge since you’ve experienced the same code and similar issues. My Bluetooth is disconnected, the Hfl is also disconnected and the alpine amp is as well. I believe I did have a used ELD replacement done about 6 months ago but the problem never fully corrected and the ground wire was just discovered and corrected 2 days ago.

07ARDI

Hey JCash23,
Sorry to hear you are having similar problems its frustrating and difficult to nail down. Which ground wire did you replace. There are several on these things and I can't emphasize enough that they are need to be good and clean. Voltage variations occur while the car is running can be a result of your ELD electrical load detector. From what I understand the voltage changes based on the demand. To what degree it happens and is normal is another thing. I would suggest checking the voltage changes now that you have the Battery, alternator and Ground fixed.
Hopefully, the new alternator, battery and ground cable fixes your issue. Replacing the Relays probably wouldn't be a bad idea but if they are going bad it is probably a symptom not a cause in my opinion. You can test relays, but it might be worth doing it and keeping the others handy if you need one in the future. Keep me posted I am interested to hear what you find.
Also don't underestimate the battery cable connections. Make sure they are clean, tight and making good contact.

JCash23

I’m

This is what was left of the ground wire that’s been replaced
going to recheck everything again this weekend, I’ll keep you posted, I did order the three AT pressure switches too, I believe I read that a failing one could set off some voltage issues. I’m pretty certain the original weren’t ever changed, I’ve only had the car since March 22 and have been doing little PM at a time, since purchasing. Thank you for replying back

07ARDI

Ha, yep that looks pretty bad. Interested in hearing more about the AT pressure switches. Keep me posted. I will add anything that I find or think might be helpful from my end too.
.

yanga001

Hi There,

So from another make of car we tend to have positive battery cables go out which leads to similar behaviour to what you are stating. Alternators have a rated amperage output and should be able to support a vehicle with little to no voltage drop in an ideal setting. The conductors have a resistance of close to zero and V=IR so with high currents we see a minimal voltage drop. What can happen as connectors corrode and wires corrode is that the resistance increases. Now looking at V=IR we can see an increased resistance will result in a voltage present on the wires. Alternator with its regulators output 14.1 - 14.2 V of potential difference between the ground and the positive output. In a perfect world, the current flowing out goes to the devices that require it (AC, electronics, ignition etc) and comes back. By design the voltage drop should be minimal. What may be happening in your case is a loose connection is now increasing our R between wires so when we increase our load and therefore current, we have a phantom voltage existing on our wires. To test this may be a bit difficult as you need to check the difference in voltage between the alternator positive contact and the battery positive contact. This should be zero, but can substantially increase if a positive battery cable goes out.

The summary of the above is bad wires or corroded wires can result in voltage drops which result in lower charge and power to the remainder of your system.

TEST PROTOCOL:
i) check voltage under no load at battery
ii) check voltage under full load (heaters, ac etc) at battery
iii) check voltage at alternator output
iv) check voltage between alternator output and battery positive terminal

If i and ii are the same then no issues
if i and ii differ by more than 1 V then I would say you need to go to test 3
if iii and ii are different during a full load test then its likely you have a bad cable
if iv is greater than 0.5V then you have a bad cable, note this should be zero.

Hope this helps