Bhavin

Hello everybody,

I have 2009 TL SH-AWD (keyless version w/tech). I removed HFL/BT unit based on all the research, car was able to start, and still battery died over night (car was dead in morning). While HFL could be the problem, something else is also drawing much power and its still killing my car while it's off.

To be exact, fuse #15 (name: Back Up) under hood seems to draw the most at 0.8amps while car is off. If I remove this fuse, car won't even do anything (no electric power to anything)... pressing start button does nothing.

Therefore I can't remove this fuse, but would like to track all sub-components, sub-fuses to see what's drawing the current.

Does anyone have power distribution (fuse connections) diagram for my car type? Please send me so I can debug this issue further. Such diagram would help me check every subcomponent that is connected to fuse #15.

Picture of my fuse box under hood is attached. Please help if anyone has experienced exact same issue before... or have the diagrams I need.



Thanks.
Bhavin.

dgy

The name suggests it powers the ECU memory (and other standby systems).

... which would be consistent with its use to power the standby parts of the electronics (the electronics have to "examine" the start button to know when you are pressing it; it's not like a light switch in a house!)

Well, you can remove it and see if the symptoms change. If your problem lies elsewhere, then the fact that you can't "do anything" won't interfere with that diagnosis.

First step is to put a figure on how long your battery "lasts" without fuse 15 in place. If it still dies, then likely 15 isn't the (sole) problem.

[If someone can comment on how much current they see from fuse 15, then you could get an idea as to whether or not your 800mA is a "good" number]

Note that you can get a general idea of where current is flowing if you have a sensitive DVM and a pair of sharp probes: connect one to the battery positive and pierce the insulation of a conductor known to be at +B. Voltage drop will be proportional to current passing through the cable from battery to that point.

But, these will be very small voltage differences. E.g., an 18AWG wire is about 6 milliohms per foot. So, if there are 5 feet of wire between you and the battery terminal (which is pretty easy without even passing through the firewall), that's 30milliohms. An amp would show up as 30millivolts drop (800mA would appear as 24mV). Yes, a painful way to check but possible without any documentation. (connectors passing through the firewall are a good place to probe -- access the connector pins on the backside of each wire as it passes into the connector)

You can also probe to see which conductors are carrying current when the car is "on" and contemplate whether or not they should STILL be doing so when power is "off"!

Showkey

Not sure where your at in the skills and tools ???

There are 100’s of YouTube videos in finding parasitic draw. Each one has tips and tricks. Guessing circuits or devices is good not choice. Careful measurement and isolation is required.

VERY short course :

You need ammeter preferably a DC clamp on version. In series ammeter will great if used exactly and correctly……..it will toast the meter or meter fuse if used in the wrong setup.
You need to understand measuring amps and milliamperes. Understand normal draw is 25-70 milliamperes or .025 to .070 amps. Understand the meters scaling or auto scaling. Decimal point and two or 3 digit display.
You need to setup the car to correctly measure the draw……….by getting all the modules in the car into sleep mode. Doors and hood locks armed, etc

Aftermarket wiring like lighting, radio, amps, alarm and remotes start kits are notorious.

dgy

"Careful" is a misleading term as it implies accuracy. In general, any fault will be "significant enough" that accuracy isn't necessary. [U}Care[/U] is required just to keep track of what you are actually measuring -- and the conditions under which the measurement is being made. E.g., if you've got a door open so you can drape your feet outside the car while you poke around under the dash, then anything powered up by that door being open has to be made note of ("Ah! I found the parasitic drain! It's in the overhead convenience lighting circuit! )

Clamp-on meters tend to need a fair bit of "working room" owing to their size. If you're trying to isolate a single conductor in a taped (or sheathed) harness, this may be impractical.

It also requires interrupting the power to the circuit being examined while you "replace" the fuse with the ammeter. And, as you are more likely to accidentally short the far (load) end of the meter to chassis while poking around (than the circuit would normally expect to encounter such a short), you really want to make sure you keep the fuse in the circuit IN ADDITION to your meter (so, if you DO touch the other probe to something you shouldn't, the fuse is still there to protect the circuit). This tends to make things a bit harder to juggle.

This is why I prefer looking at IR drops, instead. It requires a bit more thought (and basic arithmetic skills) but is considerably safer -- the meter operates in high impedance so not likely to damage anything (nor require interrupting any circuits).

First step should always be THINKING about the problem. Have you changed the car's configuration -- esp recently?

Showkey

It was the quick version.

Use the clamp on the negative terminal.measure all the draw…..not under the dash.
Accuracy often trips up the DIY. Example two digit clamp on measuring. .03 amp passes but it could be .030 to .039 which still passes.
Door open or hood open trick the switch by close the latch with the doors open.

Thermal for the DIY is asking a lot.
Votage drop over individual fuse is another technique……….but………again require accurate tool and measurement.

Honda ETM …….Electrical Troubleshooting Manual would be resource to see and understand every wire every connector, every module.

dgy

That gives you total quiescent draw. "Oh, my! Something is drawing power and killing my battery!" (but, we already KNEW that!)

You want to be able to see WHERE the current is being drawn. So, you need to be able to look at each "branch circuit"... downstream from the fuse block.

"Thermal"? WTF??

"IR" is Current (I) times Resistance (R) which resolves to the Voltage drop across that resistance. I.e., the more current through a particular resistance (like a WIRE), the larger the voltage drop across that resistance.

To get bigger values (on meter), you want to find bigger resistances -- longer lengths of wire to monitor the voltage across (the length of).

An 18AWG wire has about 6 ohms per 1000 ft (at ambient temperature). So, 0.006 ohms per foot. If you look at two points that are 5 feet apart on that wire, there will be 5 * 0.006 ohms (0.030) between those points. For a 10 ft length, there will be 0.060 ohms. If there is 0.8 amps flowing through that 5 ft length of wire, there will be 0.8 (I) * 0.030 (R) = 0.024 volts dropped along its length. A 16AWG wire exhibits less drop because the wire has a lower resistance per foot (0.004 ohms). But, you can still get an idea of where the power is flowing because most (modest) power carrying conductors will be similarly sized. (the wires feeding your headlights or starter will be larger and lower resistance)

That's the IR drop mentioned, above. Smaller ampacity fuses will have higher resistances -- so they melt easier. Power dissipated in a resistance is I * I * R (or I * V as V = I * R).

One needs to THINK about what you are seeing -- and why. The "backup" current should be ~0.050 - 0.1 A. That's about 1W of power (power is the measure of WORK being done per unit time... by whatever is using that power!) Your TV, computer, etc. at home draw ~1W when "sleeping" (waiting to be turned on).

The OP's observation of 0.8A is almost 10W! That suggests that something is "doing something" when it should be "sleeping". Something dissipating 10W will be REALLY warm. An old-fashioned "nigh light"/XMAS light bulb draws 4-9W... imagine holding one of those in your hand!

Take car out to an open space. Remove all electronic devices from your pockets, the glove box, console, etc. Turn car off. Wait for processor to go to sleep. Measure.

What happens (to the current on the BACKUP fuse circuit) when you bring your key fob up close to the door -- or the START button? WITHOUT trying to open the door or start the car.

csmeance

did you get any new windshield work done or Notice water leaking?

csmeance

Follow the white wire for fuse 15, unplug the module or check to see which one stays warm while the car is off, locked and in sleep mode.