Simon Manley

Honda Parasitic Battery Drain

This is a story about a Honda Civic with a parasitic battery drain that would deplete the battery to below eight volts in about two days. That’s a massive drain!

Attempts by other workshops to fix the problem were ineffective — real shot in the dark stuff to be honest — including installing a larger battery, randomly disconnecting lights and other accessories, and disconnecting the battery when the car was left idle for an extended period. And showing the customer how to do this so they could still use the car (insert rolling eyes emoji)

Oddly, no one performed a parasitic drain test with an ammeter to pinpoint the faulty component.

Initial Testing

The first step was to verify the customer’s complaint. I carried out a health check on the battery, which it passed – it was new. Then I checked the draw using a clamp meter to see what level of current I was dealing with. This isn’t the most accurate test, but it told me the size of the draw.

The draw on the battery was around 300 mA, which is quite substantial and should be easy enough to find. But as I continue testing, I noticed that the draw was intermittent. That can make it a little trickier — and maybe why previous attempts were unsuccessful.

Getting some real readings

At this point I connected an inline ammeter on the positive battery terminal. I used the Snap-On Vantage Pro because it has an amp graph — which I like — and it has a mini 10A blade fuse in case I turn the ignition on or whatever and pull too many amps — it’s easier to change this fuse than on other tools I own so I like the set up.

I noticed the 300 mA draw would come and go, so using a graphing meter can be helpful to show a full trace and if there’s a rhythm to the on/off or is it just a fault with no repetition. This method also allows me to lengthen the timebase and see what’s happening over a long period.

What I do in this situation is latch all doors — this is easily done with a screwdriver, or similar, pushed into the lock to simulate it closing and latching — now I can open them without waking anything up, like interior lights or fuel pump primes, etc.

This gives me the ability to access interior fuse boxes or other electrical components I may need to get to for testing purposes.

Finding the faulty circuit

With everything in place I can test the circuits for a culprit. I sometimes do this with an Amp Hound or with a normal Multimeter. The Amp Hound is a quick way of doing it usually — but I have had times were small draws were not seen — in this case with a larger draw I was sure it would work just fine.

It ended up taking a lot longer than it should as I noticed the draw would drop off quite frequently — which was frustrating — but eventually I pinned down a suspect circuit.

Now to find the cause

The draw on the battery is coming from Fuse 9 (F9) in the engine compartment fusebox. This is a 10 A fuse for Wash/wipe, Instrument cluster, central locking and audio system circuits.

When I first looked at this car I expected to see an aftermarket radio/head-unit — I’ve fixed so many battery drains by removing these units — but that’s not the problem here, the original factory unit is still in place.

Although not the case here, one lesson I’ve learned after years of chasing battery drains; the most common causes are aftermarket junk.

I’m at the point now where I have to make a decision and take something out of that circuit to see if the draw goes away.

The easiest to disconnect — and frankly the biggest suspect — is the audio head unit. It’s a bit of work as part of the dash trim had to be removed but it’s the most straightforward of the options.

Sure enough when I get it disconnected the draw disappears straight away. I’m excited and happy for this but there is an element of doubt, because the drain did go away and come back while I was testing earlier.

I left it overnight with my graphing meter connected on a really long timebase, when I came in the next day, the battery had maintained its charge and the graphing meter showed no signs of drains.

Conclusion and wrap up

On one hand I wasn’t surprised at the outcome — I’ve seen this before — and although I did find that it was (slightly) intermittent and not straightforward to find. It could have been found by the previous places if they just looked properly.

But they made assumptions as to what it could be, spent money on a battery that probably wasn’t needed — I don’t know how old that battery was and maybe it needed replacement for testing purposes, that is a reasonable thing to do — but just unknowingly unplugging this or that and then telling the customer to disconnect the battery overnight as a solution is, frankly, ridiculous.

Fuel Injector Waveforms and Information

This is a section of the SST 1500 manual on fuel injectors, their waveforms and some general information. These are photos of the pages — I am starting to scan them to create a PDF — but someone wanted me to send them this info so i’ve put it here for that reason.

I love that one of the pages has hand written info in ballpoint pen from the previous owner.

Expanding the diagnostic cart, old meets new

I made a mount for the SST to accommodate the Verus. I can also mount the Pico/Toughbook set up I have.

Using it in a real world situation will be the test but I like the idea of having this as a full diagnostic cart set up.

Monochrome Screens and Photos Don’t Mix Well

Trying to take photos of this screen is tricky; I assure you it looks fine to the naked eye, but my camera/phone is not happy taking them.

There are ways I could take it by setting my camera to manual mode and adjusting settings, but that also would require a tripod. I’ll set it up when I have it finished.

Anyway, it’s now running on A/C power. These machines were designed to run from the vehicle battery, and that’s fine once you have it hooked up to and are working on a vehicle. But I wanted to explore functions with some bench tests while I learn its limitations, and it’s just not practical to pull my car in every time I want to do that.

The answer was an AC to DC plug-in of some sort. This sounds easy, and it is, but getting the right power unit wasn’t easy. Partially because I wanted to go to a shop and pick it up, I’m tired of ordering online then waiting days to get back to the project, it just feels counter-productive. But it turns out trying to find a power unit locally, or even within a distance because I was prepared to travel, was counter-productive.

There wasn’t one to be bought anywhere except online. And prices varied hugely. I ended up finding one on Amazon on Wednesday night and even with choosing free shipping it arrived today (Friday), which was 3 days early. Glad I didn’t pay the 10.99 they wanted to guarantee delivery today, there’s a lesson in there. It’s all set up now and running on wall plug power.

I opted for an SAE J563 connector (cigarette lighter or accessory charging port) to fit with the power unit. It keeps it somewhat standard and fits well with the same connector I have in my power probe kit, so I can still hook it to a 12v battery if needed.

More photos on page 2