civic2007Ex

We have a 2007 EX with 190000 kM (118,000 miles) on the OD. It serves us as a toad while we Snowbird in AZ.


In the 10 years that we have owned the vehicle we have had about 3 to 4 episodes where the battery has somehow drained mysteriously over night or over a couple of days. We are on our 3rd battery, the current battery was purchased from a Honda Dealer 2 years ago.


Now for the latest episode, yesterday.


The vehicle has been parked (in an heated garage) and sat unused since September of last year. Two weeks ago I was in the vehicle to update the registration and I was particular in sensing the state of the battery. The battery was definitely in a good state of charge judging from the door locks, the interior lighting etc. I did not start the engine because there way no apparent need to test any further.


So, now, two weeks later, the battery is so dead that there was not a bit of voltage left to trigger a charger until I got the jumpers out and started the engine. The battery was dead, dead, dead and then some dead.


So, what are the chances of:


1. The door lock electronics are acting up and killing the battery, or maybe


2. The battery drain was caused by a defective AC clutch relay which would have been subjected to a vibration associated with opening and closing doors, once again, the engine was not started, or maybe


3. Something else.


I know there were no lights left on because I am very careful due to the history of the beast.


Thanks for any insight.

civic2007Ex

Is there an Omron Relay (PN 39794-SDA-A03) used with the powered door locks of my 2007 EX Civic?


If there is then I suspect it is the cause of a very intermittent unexplained battery drain.


Thank you.

civic2007Ex

OP Here.


After further research I am thinking the door lock circuitry could be involved and I have been searching for a "door lock relay".
All I can come up with is references to a "door lock module". Does anyone know where the "door lock module" is located in a 2007 Civix Ex 4 door sedan?

CraigW

iTrader: (1)

Pretty certain that relay is enclosed inside the MICU. Not replaceable as individual part. (only entire MICU)

ezone

This alone is the cause of your battery problem.

The car has several items that use very little current, but over time that little bit of draw will drain the battery.
Hell, if you just leave the battery sitting still for an extended period, even without it being connected to anything, it may still discharge itself.

Leaving the battery in a low state of charge will ruin it. It was never designed to be left that way, nor was it ever designed to be drained completely. The battery was designed to supply a whole bunch of current for a short time (run the starter) , then be recharged immediately by the alternator.

A lead-acid battery needs regular maintenance, which is periodic charging.

If you wish to leave your car sitting for months at a time, get a battery maintainer and keep it plugged in.

This is in NO WAY any sort of test, nor confirmation as to the battery state of charge.

The only thing this indicates is that the battery had just enough power to operate a few very low current electrical items.


Had you attempted to start the engine at that time, I expect the battery could not supply (roughly) 150 amps of current necessary to operate the engine starter for up to 15 seconds.

The very brief 2 amp load to run the locks and dome light is a far cry from 150 amps needed to run a starter.

Bet.

We have to test the batteries in all of the brand new cars on our lot every 30 days. Charge if necessary.
If the cars sit unused long enough, they will all drain their batteries sooner or later.

civic2007Ex

Thank you ezone, I value your input.


But, I do have 55 years experience in electronic hardware and have owned 3 different Honda Civics starting in 1990 so I think I am a good judge of the symptoms.


What I really need to know is what Omron Relays (if any) are involved in the locking and unlocking sequences, ie dome lights, horn, dash lighting etc etc

ezone

None.

The power locks and keyless entry controls have no external serviceable relays, the relays they do have are internal to and controlled from within the Multiplex Integrated Control Unit or MICU (one of Hondas body control systems, part of a network of control units throughout the car).

Horn relay is internal to the same MICU as are the relays/controls for headlight high and low beams, dimmer, daytime running lights, park lights, turn and hazard lights, flasher, interior lights, entry lighting....and more.
Then you should own a low current ammeter and know how to use it. Yes?

Prove you have a problem before wasting time and money needlessly.


With a good fully charged battery installed, connect the ammeter in series with either battery cable and find out what the true draw is, in milliamps.

Leave the windows down. Flip the rear seat down so you can see into the trunk
Remove the keys, make sure everything is turned off, close all the doors, use a screwdriver to close the hood latch (while leaving the hood raised to do your work).

Connect ammeter.
(My favorite for this is a clamp on inductive ammeter, an 'amp clamp')
If you have to break into the battery cable circuit to connect your ammeter, you will then need to wait for all of the control units in the car to 'time out' or go to sleep, switch themselves to low use state. This should take less than 20 minutes on an 07 model year Civic, probably more like 5-10 minutes.

Take readings. If your meter is quick to react, you can even 'see' the meter show the intermittent loads of the blinking red light on the radio, and the blinking red light of the car alarm in the upper gauge housing.

So your draw test results should be as follows:
Industry standard is 'less than 50 mA' for most cars on the road.
On a car like yours, I'd expect to see a draw of less than 30mA after all of the computers time out.


Now calculate how many days it would take to drain a fully charged battery with a 30mA constant dark current.
Then recalculate this length of time using a partially drained battery that is a couple years old and only has half its rated capacity-- instead of a new one.



--------------------------

Something else that could have happened.....let me toss this scenario out here:

All of the computers rely correct voltage from a good battery in order to do their jobs correctly, you would agree?
But since the car sat for 6+ months unused, the battery was weak, the battery was in a low state of charge, say maybe 9-10 volts--that is enough to work the power locks and dome lights, but.....
When you "woke up" all of the control units by opening the car, any of the microprocessor controls could have been adversely affected by the low system voltage and not done their usual job correctly, remained awake, unable to 'time out' correctly, left unfinished business on the data bus, etc.

This could have increased the amount of drain on the already weak battery.

I can't say this is what actually happened, but microprocessors do tend to freak out and do strange things when trying to operate using incorrect source voltage, and they sometimes go haywire with voltage spikes.

What's your background? (If you don't mind me asking.)

mcnoople

55 years ago vacuum tubes were commonplace. Maybe a vacuum tube has failed?

Where are omron relays used? Everywhere. They are used in fuse boxes that are replaceable. They are used inside of control units soldered directly to the circuit boards. Their failure rate when used to control circuits (other than AC clutch circuits) is tiny. They make a good relay, but it doesn't survive in the AC clutch circuit.

Your AC relay would not have engaged and and stuck on unless you started the engine and the HVAC control head decided to send a signal to the magnetic clutch.

Buy a battery maintainer, leave the battery disconnected from the car when it is going to sit for more than a month. Do those 2 things and your batteries will last for years. Park it and ignore it for 6 months and you WILL replace batteries every year or two.

civic2007Ex

I really do appreciate the replies.


This is the first year we did not do any Snowbirding AND the car is/was parked inside our heated condo parkade, so I was not concerned of freezing a low battery... The normal parasitic current in this car measures 7 mA (x 24 x 180 days = 30 Amp Hours).


Remember this problem has been with me for "3 - 4 times in 10 years" of ownership. On the previous failures it was an over night discharge.


Yes, I started out learning on vacuum tubes and germanium transistors. The National SCMP was my first microprocessor in the mid 70s.


When Bill Gates was doing his Tic Tac Toe game on main frames I was doing my Tic Tac Toe game in machine code with my Heathkit H8 micro interfaced to my Heathkit Dual Trace Scope as my game board. The only reason this was possible is because the Heathkit Scope had a beam ON/OFF control input.


My electronics career was in Industrial Electronics in the oil and gas industry. We installed our first solar powered well head control systems (gas wells in remote tundra) in the 90s. And my favorite line is "if you are going to talk about solar power then 90% of the discussion will be about batteries".

civic2007Ex

SO, maybe:


This latest experience could very well be the "low battery vs microprocessor" "well spoken" scenario by ezone.


The previous experiences could very well have been caused by the AC clutch relay. I am assuming the AC clutch is an inductive load without a snubber diode.


So, I think I will replace the AC clutch relay and go from there (and yes I will not push my luck with any more 6 month storage stints).

ezone

That's to completely discharge the battery, yes? (did not math)
But a half discharged battery may not be able to start the car.
So......you might figure 3 months or less before the battery needs to be jumped to start the engine.
Plus, a discharged battery physically deteriorates internally as it sits (google 'battery sulfation') and if left in a state of low charge long enough, may never fully recover.

Your assumption is correct according to the wiring diagrams, and I've often wondered why these engineers did not put a diode in the circuit for spike suppression.
The AC clutch field coil circuit is about the only thing that particular relay (Omron brand) commonly has issues on, and rarely any problems when the exact same relay is used with the dozens of other applications in the rest of the fleet.

There is service info about this, the updated relay is made by Mitsuba.
Honda part number for the Mitsuba relay is 39794-SDA-A05.

Clutch relay is position 12 in the diagram below: