Driving (or, trying to…) a 5sp manual 2001 Honda Civic. It has had some electrical issues in the recent past, currently has a nearly new battery (~3 months old), and a new alternator less than 1 year old. Lately, the battery repeatedly drains overnight or over just a few days. It will start and run fine with a jump, and I just took it on a 3 hours drive and it handled it with no problem, so this pretty definitively rules out the alternator (which is new anyway).
My first suspicion was a parasitic draw, but when I try to measure it, nothing! Here’s what I did: unhooked negative battery terminal, and used a multimeter to measure current from the negative cable to the negative terminal. As far as I can tell, there is NO current being drawn when the car is off (should I be suspicious that it is 0A?). When I first connect the multimeter, it will show ~100mA which quickly goes down to 0mA after a few seconds (even in uA range, it is 0.000…). To make sure the multimeter worked, I turned on a few car lights, the radio, etc. when the meter was connected and the current indeed goes up.
My first thought was a bad battery, but I took it to Walmart to get tested, and it tested fine… Remeasured it after it was charged and tested, and still 0 amps. This made me think that maybe the ground connection is bad, so I tried testing the connection with the meter, but it seems fine (relatively low resistance, meter beeps when touching to ground cable terminal and chasis mount points).
I’m kind of at a loss here… not the alternator, not the battery (assuming a Walmart test is definitive), but no draw of any kind when the car is off. However, there is no current measured at uA scale when stopped… which is weird to me. Any thoughts?
A better diy’er test for the alternator is: before first start of the day the battery posts should measure about 12.6 volt. Immediately after starting the engine they should measure 13.5-15.5 volts.
re: parasitic draw, no current measured. an 01 civic I’d guess would be in the 15-50 mA range. my older corolla measures around 6 mA as I recall. Perhaps the current scale you are using on your meter doesn’t register to 50 mA. 50 mA = 0.050 A. make sure you are using the dc, and not the ac current mode.
When you turn the radio and increase the volume a little louder than you’d normally listen, what’s the drain then? caution, turning on a high current device like the headlights could damage the meter when it is in-series w/the battery like that. When I’m checking the corolla the way I tell the meter is working is opening the door, which turns on the dome light. the dome light is maybe a 5-10 watt light bulb, so a little less than 1 A. (1000 mA).
ground connection: does the parasitic current measurement change if you connect the meter to the chassis ground rather than to the battery ground cable?
There’s one weird possibility that can drain the battery w/no indication of parasitic draw. That’s if the battery is coated with a conducting film, like old battery acid. The current will drain right from the positive terminal to the negative terminal across the surface of the battery. cleaning the surfaces of the battery w/a weak solution of sodium bicarbonate and a flush w/plain water can help w/that.
My guess is there’s a ground problem and/or the alternator isn’t working 100%.
This is not so uncommon, depending on where the battery is. But this battery is only 3 months old, so not likely unless it’s gotten or getting wet or dirty.
re: parasitic draw, no current measured. an 01 civic I’d guess would be in the 15-50 mA range. my older corolla measures around 6 mA as I recall. Perhaps the current scale you are using on your meter doesn’t register to 50 mA. 50 mA = 0.050 A. make sure you are using the dc, and not the ac current mode.
I tried several of the different scales (from A to uA, and even in the uA scale there was nothing), but good point about DC vs AC… I’ll need to check again making sure I was in the right mode.
I will do the other sanity checks for the alternator and testing the meter with some things powered on and get back to you!
re. the battery, there actually was a fair bit of wetness underneath the battery (I think it was just moisture, not acid I hope…)
The way you can check if charge is being lost over top of battery: put red probe on positive battery terminal, black lead near but not on negative terminal. If there is voltage, clean top of battery with baking soda and water. Don’t get carried away and douse the battery with solution, too much is bad.
I’ll bet the running voltage is low.
There’s no parasitic drain because a branch of the B+ “always on” has an open circuit.
Does the radio retain its presets?
Could be just a blown fuse.
Where’d the replacement alternator come from?
It drains every night?
I’m an idiot, and the multimeter I’m using defaults to AC current. When I switched it to DC, sure enough there was about 90mA draw when everything was off. Started removing fuses and it was the ABS motor circuit that was the culprit.
Anyone know where to start with diagnosing electrical issues with the ABS system?
I think you’re gonna have to acquire an ABS capable scan tool for your car to do much in the way of diagnosis yourself. The ABS systems on cars these days often stay powered for a short while on even when the key is off, for self testing purposes. But should turn off within 30 minutes max I’d guess. Make sure you are waiting 30 minutes after you turn things off before assuming you have an ABS malfunction.
Note that it would take quite a while to drain a good battery at 90 mA. Most fully charged batteries have about 30 amp-hours of useable charge, and it would take nearly a full 24 hours to drain even 2 amp-hours from the battery at the 90 mA drain rate.
Good to know re. the drain rate. I suspect the battery hasn’t been fully charged until recently (when we got it tested), given the drain. I think it is usually sitting about a week before it is unable to crank, so I suspect the drain is the main issue.
When I did test the drain earlier today, it was after the car had been sitting turned off for two days (negative lead disconnected, to prevent anymore drain). So I think the ABS malfunction is real (that, and the ABS light turned on a while back, right before I started experiencing these drain issues).
Are there any auto supply stores that will scan the ABS system??
When you installed the meter in the negative battery connection that powered up the car’s electronics again, and when that happens all the computers including the ABS computer goes through a reset procedure. Best to wait 30 minutes after that to determine phantom the drain current.
Thanks all for the help so far. I’ve finally had time to get the ABS code scanned.
The first scan showed two codes:
15-1 Right Rear Wheel Speed Sensor Open Circuit
54-1 Fail Safe Relay Failure
However, the mechanic restarted the car, and scanned again, and only the first code (15-1) showed up on this second scan. When I told him I’d like to check/replace the faulty sensor myself, he recommended to also replace the relay at the same time. I’m not entirely sure where this relay is, or whether it actually needs replacing, given that its code was inconsistant.