Car-related puzzle involving dead battery and maybe rats

January 17, 2018 7:00 AM

Can anyone explain the following sequence of events involving my car, a dead battery, power steering, and potentially some rats? The car is a 2013 Honda Fit with low miles (it sits a lot, probably relevant):

1. Car battery dies. We later found an interior light on and the car sat for ~2 weeks, so this is the most likely cause. I'm supposed to leave for holidays the next day and so I just decide to ignore it until I come back.
2. After I return I'm able to jump the car using a booster battery (didn't have this yet in step 1). The battery is dead at this point, I have to put the booster into its override mode since it can't detect a battery at all. I go to drive it for a while; at first things seem normal, but power steering starts flickering/failing, which is pretty unnerving since this car is steer-by-wire. Eventually while pulled over somewhere, I discover that if I turn off the heat power steering works, it's sort of like turning on the heat causes a brownout or something, all the console lights dim as well (later I discover that headlights also have this effect too). I limp home. The manual suggests that if you get the power steering light, first try turning on and off the car and see if it still happens. The battery doesn't seem to have charged. Because it's 9F, I decide to wait a few days until I know it will be a lot warmer in hopes that it's just something to do with the extreme cold.
3. At this point a neighbor tells me that she's seen rats going in and out of the engine compartment. Mild panic, envisioning thousands of dollars of electrical repairs... (apparently Hondas in this model range use bio-polymers for wiring that animals sometimes like to chew.) The building owners have put out some poison / tried to take steps to minimize the rats.
4. A few days later, when it's above freezing, I do try to charge it again, and discover that (at least at idle) the effect of heat/headlights on power steering is quite deterministic. The battery holds a bit of charge but not much, and I don't feel comfortable driving it at speed. The battery's 5 years old so I figure it needs to be replaced in any case.
5. I take the car to a mechanic (the dealer). They replace the battery, find and clear the power steering failure code, and spend a fair amount of time tracing wiring. however, they don't find any evidence that rats actually chewed wires! There's some minimal evidence that rats were in there (and I've noticed since that when the engine's warm it kind of smells like animal piss), but no evidence that they've interfered with the electrical system or nested in there or anything. The car now works. Side-note: I didn't have presence of mind to have my car still running and show them the symptoms when I dropped it off, so I'm not entirely sure they believed/understood my description. They believed the code, though.
6. The car just continues to work normally??

I'd like to know if this is going to come back, and what steps to take about the rats. Is there something other than animals messing with the electrical system that could explain the power steering problems? Honda has some kind of pepper tape for wiring, but the mechanic didn't want to install it without seeing something that was actually chewed on. I'll try peppermint oil too, I guess, but I somehow am skeptical that that's going to intimidate Baltimore city rats. Right now it's sitting again for a couple weeks while I'm away, but this time in a non-urban airport lot where hopefully the rodent population is smaller.

posted by advil to Travel & Transportation (11 answers total)

I don't have any answers about what's going on, but if your car is ever damaged by rats your insurance might cover it. I had a chipmunk chew through a gas line and I called my insurance about it. They covered it in full, including a replacement rental. (though I had replacement coverage on my insurance. YMMV)
posted by bondcliff at 7:06 AM on January 17, 2018 [1 favorite]

It's not clear why you're still thinking that rats caused the problem, given that the wiring has passed inspection and replacing the old battery seems to have corrected the issue.
posted by jon1270 at 7:07 AM on January 17, 2018 [2 favorites]

Best answer: Sounds like your battery may have frozen while it was dead. This is often a permanent death sentence for car batteries.

If it has a full charge, your battery can withstand temperatures as low as 76 below zero. If it’s fully discharged though, (in other words, it has a charge of 12 volts or less), it will freeze at the same temperature that water freezes.
posted by solotoro at 7:15 AM on January 17, 2018 [3 favorites]

Response by poster: It's not clear why you're still thinking that rats caused the problem, given that the wiring has passed inspection and replacing the old battery seems to have corrected the issue.

Because otherwise I have no explanation for the power steering issue? I mean, I'd definitely prefer to believe that rats didn't cause the problem...
posted by advil at 7:31 AM on January 17, 2018

I had an identical battery failure (though I didn't try driving before battery replacement) - interior light causing complete drain in freezing temperatures and a battery that just wouldn't charge anymore. I also had an unidentified animal nesting in the engine compartment because the critter brought in pieces of bread O.o The car has been all right for two years now. I recommend getting the engine scrubbed clean amd knocking on the hood before starting the car. (I also have an idiot cat.)
posted by I claim sanctuary at 7:32 AM on January 17, 2018 [1 favorite]

Best answer: it's sort of like turning on the heat causes a brownout or something

Basically exactly that, as I understand it. Battery can't take a charge, your alternator's going overtime, your power steering shuts off when the alternator can't keep up with everything. You don't have a separate power steering problem. You had a temporary alternator problem because of the battery.
posted by Sequence at 7:36 AM on January 17, 2018 [9 favorites]

Best answer: Yeah, the initial dead battery was so damaged* it could not be resuscitated, at least to full capability. The battery/alternator combo couldn't run every thing at full load, as Sequence says, and that explains your symptoms. And also, why they went away when you dropped in a new battery.

*Possibly by the cold, possibly too long sat discharged, possibly just age, or a combination thereof. I would have made the same choice you did not to deal with it before travel, the new battery just isn't that big a deal.
posted by stevis23 at 7:59 AM on January 17, 2018

Best answer: The battery caused all the problems. It never charged correctly after the full drain, so didn't have enough muscle (basically) to run lots of electrical systems at once, because the car was basically driving on the alternator. Your brown out analogy is exactly right. This is why the car is working normally after the battery was replaced. The rats are a complete distraction/irrelevance if the garage found no evidence.
posted by Brockles at 8:36 AM on January 17, 2018 [4 favorites]

Best answer: The battery is dead at this point, I have to put the booster into its override mode since it can't detect a battery at all. I go to drive it for a while; at first things seem normal, but power steering starts flickering/failing, which is pretty unnerving since this car is steer-by-wire. Eventually while pulled over somewhere, I discover that if I turn off the heat power steering works, it's sort of like turning on the heat causes a brownout or something, all the console lights dim as well (later I discover that headlights also have this effect too)

Batteries have an internal resistance, like everything else (lights, etc.). When they are flat, this is much higher. That means that when your battery is low, the alternator has to work harder to deliver enough current to run everything and charge the battery.

Alternators are not magic - the amount of current they can generate is directly related to engine RPM. The faster the engine goes, the faster the alternator goes, and the more power it can put out. In the future, don't drive at 25mph to charge the battery, get on the freeway and shift down a gear or two and tach the engine up. The faster the engine goes, the more power the alternator can produce.

Batteries don't just provide power to start the car. They also act as capacitors to help deliver current, and even out spikes in power draw (like using the brakes, or turning on high beams). The alternator cannot respond immediately to instant increased demand, so this causes the voltage to fluctuate at that moment. The inverse happens on the other side - you get an overvoltage spike when the draw goes away. This is why a dead battery is often followed by a bad alternator - those spikes in load are really bad for the alternator. I wouldn't be surprised if you find you need that replaced soon.

Power fluctuations have all sorts of knock on effects for the sensors and such (this comment is too long already, but I'm happy to explain it), and I'm not surprised you saw much weirdness driving around on a flat battery. In the future, if the battery is flat, get the car started and run it at 12-1500 rpms (your foot on the gas) for a 10-15 minutes before going anywhere. Then run for 30-40 at highway speeds (~3000 rpm). Or put a good battery charger on it.

TLDR - Flattening a battery like this can permanently damage the battery. Driving around with a flat or disconnected battery is REALLY bad for the electrical components in the car, especially the alternator and various computers and sensors.
posted by Pogo_Fuzzybutt at 8:57 AM on January 17, 2018 [3 favorites]

In my experience, you only ever find out that you have a charging problem when it's cold, dark, and rainy, and all of a sudden your wipers don't want to move as fast and your headlights are dim. Electric power steering is just another thing to add to the list. (In Ye Olden Days, the power steering pump ran off a belt, so would fail in a different way.)
posted by Huffy Puffy at 9:25 AM on January 17, 2018

It's good that you replaced your battery. In my experience, when a battery freezes, you can sometimes get it going again by thawing and charging it. You think, "great, I don't have to buy a battery". Then, in April, at some very inconvenient time, it turns into a brick.
posted by H21 at 11:17 AM on January 17, 2018