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.

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.