New method of parasitic draw testing leads to diagnosis of battery-killing Honda
While employed as a sales representative for a diagnostic tool manufacturer, I remember coming across a particular gentleman to whom I was trying to express how important it was for us to keep changing along with the vehicle technology confronting us. If I recall, he went by the nickname “Cooter” (hi Sam!). In a way that I thought he would comprehend, I strived to express how doing things the old-fashioned way on modern vehicles simply doesn't work. I mentioned computer-controlled alternators and then he interrupted me.
Vehicle Information: 2015 Honda Civic Si
Engine: Rice Burner 2.0L L4 DOHC
Trans.: Manual, 5-Speed
VIN: 2HGFG4A57FH704743
He took offense to what (I believed at the time) was an educational opportunity, and let me know with a reply of "Are you calling me stupid? You think I AM stupid, don’t you? I've been doing it this way all my life! I don't need to be spending my hard-earned money on your high-priced equipment!”
Of course after that there was no point in continuing to convince him that sometimes employing the old fashioned ways may not be a wise choice and they may actually cause more problems than they solve. There was simply nothing I could say to “Cooter” that would help him understand he could improve the way he was diagnosing vehicles or to get him to consider other ways that would accurately and efficiently diagnose today’s vehicles.
As I was leaving his shop, I remember him trying to tell me that “no equipment could tell (him) the alternator was faulty any better than” the method he uses. He said if he “disconnected the battery cable while the engine was running then he’d know one way or the other.” Yes, I cringed when I heard that. Hopefully, you did too when reading it.
What would you do if someone told you there's an easier, more efficient way to do something that you have done the same way for a long time with excellent results? I’d say “prove it!” In most cases there's no reason to change the way we are doing things as long as they work and provide us accurate information. There are circumstances however, that make you have to change — maybe against your will!
It really doesn't matter what brand of vehicle you are working on when you are trying to address a "parasitic drain" (also called a “parasitic draw” or just a “draw”). The problem is usually that the vehicle’s battery has gone dead with no reason, within an unreasonable amount of time.
This may be that day!
In the “old days,” to diagnose a parasitic draw — on a vehicle with the key off — we would disconnect a battery cable and put a non-powered test light in “series” or in other words, between the cable end and the battery terminal. If the light lit, we knew we had a draw. If the light didn't, either the problem was intermittently occurring or we knew that something was probably left on and has now been turned off. Once sure there was a draw, we would disconnect one fuse at a time until the test light didn’t shine anymore. A long time ago the fuse blocks were fairly simple and usually identified the whole circuit each fuse protected so we knew which system was affected and would start working towards the component at fault – isolating items that fuse fed.
After electrical systems became more complex it became imperative we had to have accurate service information that included electrical wiring diagrams. With the advent of “Maxi” fuses providing many smaller fuses with protection then came the time when multiple circuits could be protected by one larger-capacity fuse. We would begin the tests the same way (test light attached at the battery), but then we’d disconnect the high amperage rated fuses one at a time. Once we identified which of the higher amperage fuses were carrying the parasitic load (draw) then we’d pull those lower amperage fuses that were protected by it one at a time.
Some of the more nerdy among us folks would install an ammeter in series instead of a test light. I found knowing how many amps draw I had helped me eliminate some circuits that could have been suspect. For example, a draw higher than one amp could not be caused by a glove box light staying on. However, do you know what problem I found when employing an ammeter into a circuit with an unknown amount of amperage flow? Yes, sometimes my meter’s fuse would blow and those weren’t cheap! Alas, I learned to use an inductive ammeter I repurposed from a farm tractor, attaching it to one of the battery cables prior to disconnecting it, and then I had a good idea how many amps I was probably dealing with before attaching my ammeter. I blew far fewer meter fuses when I did that!
Drain caused by computers?
In addition to the higher number of circuits being added to the vehicles were also computers. The “standard procedure” we were following to diagnose parasitic drains at that time was found to sometimes result in us having to write on the work orders “NPF” (which stood for “No Problem Found”). Unfortunately, very soon thereafter we had to recheck the same vehicles again and again. What was happening was a module or component was causing a draw until the battery was disconnected! They would “reset” and work as designed for a while. As soon as we placed our test lights in series, the problem was gone. Sometimes we were fortunate enough that the problem causing the draw could be recreated while the test light was still connected, most times we couldn’t.
This phenomenon was the reason we had to change our method. From that time until today, anyone that's got to address a vehicle that has a parasitic drain would typically grab a DVOM (Digital Volt and Ohm Meter) and an inductive Low Current Probe (LCP). The probe is used so that a battery cable doesn’t have to be disconnected and fuses do not need to be removed to find an affected circuit. If an excessive current draw is detected at a battery cable on a modern vehicle the combination of DVOM and LCP greatly reduces the potential for a circuit to be disturbed, thereby ensuring if the draw is caused by a module, it will continue to do so until we isolate it. We can use the LCP on circuits protected by any size fuse and work our way from the battery to the component just like we did in the “old days” using a test light.
The Halloween Honda story
I was recently called into a mechanical repair shop because a vehicle's battery was unintentionally discharging so quickly that the vehicle would not restart if it sat overnight without a charger. The vehicle owner did not correlate this problem to the collision shop repair because that had been done several months prior without any problems occurring like this since.
As if it were timed for Halloween, this 2015 Honda Civic with a Rice Burner 2.0L L4 DOHC engine and manual five-speed transmission had been repainted the “perfect” color. Several months prior to seeing the vehicle for my first time this vehicle had been in a collision resulting in extensive body work. At first I was unaware why it had been repainted that color, thinking to myself it may have been a combination of things — that the owner must be color blind and the body shop doing the job wanted to get rid of a bad purchase (lol). Turns out that “Pumpkin Orange” was the color the owner actually wanted! Well, as the saying goes, to each his own.
Anyway, I begin all of my parasitic draw diagnostic routines by checking the state of health of the vehicle's battery first. I have been burned in the past by testing systems that were acting unusual only to find their voltage was right at the border of being acceptable. Modules have a way of acting unusual without proper voltage or ground.
Having confirmed the battery state of health (Figure 1) was at 80 percent, I deemed it acceptable for further testing so long as a battery charger was attached. I proceeded to connect my DVOM and LCP to check for the draw. Seeing a 200 milliamp draw made me start considering things like a small light and other small draws. I stared at my DVOM display long enough to see a momentary display of close to 500 milliamps. It was that momentarily higher display that caused me to use the min-max function to see whether or not there was something surging in the circuit. And, yes there was.
I thought it best for me to use the Pico scope to graphically depict the amperage in order to help me analyze this parasitic draw. I'm very thankful that I did. The image captured (Figure 2) looked almost like an injector voltage waveform!
The image displayed made me somewhat confused at first. Realizing I was up against some sort of a controlled circuit, I decided to sit inside the vehicle and just observe. I was expecting something to turn on or give me a sign. Initially, none of the courtesy or dome lights were turning on, none of the gauges were flickering and the instrumentation was not displaying anything unusual as.
The thought occurred to me to cover the windshield to stop the outside light from coming in. That was the key in diagnosing this vehicle's problem. I was able to see flashes of dim light displayed on the driver information center/navigation system! It was then I decided to head for the radio fuse and put my low current probe on that circuit. That was exactly the same image as what was displayed at the battery. I’d found the culprit. Now what?
I found in the Service Information a procedure for a “Self-Test” that could be run on the Infotainment system. Surprisingly, every part of all the very extensive tests passed!
I felt it was time for a visual inspection of the unit and removed it from the vehicle. On the bench it was evident – water damage! Once the problem was identified, the customer acknowledged the windshield had been broken in the crash several months ago, and the vehicle was left exposed to the elements for many days with that condition present. We concluded the navigation audio/infotainment system had been subjected to water damage after the windshield had been broken during the collision but wasn’t showing signs of damage until rust had set in and affected certain circuits internally. A replacement unit resolved the parasitic draw. After the navigation audio/infotainment system had been replaced with a used unit, the Security light is the only draw (Figure 3).
So, in this case, as happened to me several decades earlier, I learned of a new way to help me diagnose a parasitic draw. Using a DVOM I was only supplied a digital representation of the fault, which proved to be woefully inadequate. Using a scope instead of a DVOM, I graphically displayed the circuit condition, which completely changed the direction in which my diagnosis was headed.
Again, I cannot stress enough the importance of having accurate service information when attempting to diagnose this condition (parasitic draw). A wiring diagram and sometimes a wire routing diagram as well as component location information, can make diagnosing a parasitic draw much easier!
