Mystery alarm-like tone from under the hood

originally posted by: Mandroid7

Here's another one to check.

link

the box is located on the drivers side firewall, the thread in that link is pretty good.
good luck

That's a pretty big help, this photo shows it almost in the same spot, though it's shaped slightly differently. I assume it's just a variation between year designs & the same thing either way, though, placement's fairly standard.

originally posted by: rickymouse
a reply to: Nyiah

That sounds like it may be the headlight switch left on signal. Does it make this sound when the keys are in the ignition?

Took me a second to get what you mean here, I somehow thought you were talking about turn signals. It's a push button start, not sure if it makes a difference in diagnosing, but there you go.

When the car is on, it does make the alarm-like noise. As long as the brake is lightly depressed or fully depressed when the car is running, then it does not make the noise. In between those, it does (makes for an annoying drive)
Like I said though, it still makes the noise when it's shut off, and the only way to make it stop is to disconnect the battery. So running the car or not running the car, if the battery's hooked up, or you're not caressing the brake right, it does it.

Take the butt end of a screwdriver and tap on that thing. Not too hard, but just a few taps. If it is some sort of buzzer, it would be controlled by a solenoid, maybe the solenoid is stuck on. The solenoids are usually in a fuse box somewhere, they are probably marked in your book or on the cover of the box. If it is stuck on it will keep running, and that is not uncommon, even with a fuel pump.

a reply to: drewlander

No , I can't find a vid link, just that image.

It sounds like that unit has problems by itself and the door sensors fail and trigger it.

The brakes making a difference is weird though. May be coming from actual abs actuator "brake booster pump"

I wouldn't think the draw from the brake lights would be enough to stop it.

If the pump has a pressure switch failing, it may sense the booster as being too low and over run the pump when it's not really needed, but pressing the pedal, jacking with the pressure may be enough to trigger the failing sensor.

Hard to gremlin hunt from here, but I'd start with the ghetto stethescope, aka short garden hose and try the brake/booster assy, then the power steering assist pump, then the firewall alarm box thingamajiggerdohicky.

I found something that might be pertinent. If the ABS motor is buzzing, it could be from a stuck solenoid that controls the ABS motor. I ran into a site which mentioned pulling the ABS solenoid and checking if it quits, apparently most times it is a stuck solonoid. Being that the brake peddle effects it, I decided to check if it had something to do with the ABS system. I do not know where the abs motor is in that car, it looks like a brake reservoir in that picture though, it could be around there.

The ABS solenoid should be in the fuse box. Switching it with another solenoid like the horn solenoid if they are the same number might be a way to check it.

To isolate the fault ,locate the fuse box and start removing fuses until the sound stops.
Description of what the fuse controls is usually listed in the user manual ,
or you can Google it.

I had something similar in a VW, it was a high pitch squeel and it ended up being something like a relay or some other electrical component that was a square box about 1" square and about 2" long with 4 metal connectors that plugged into a harness. I pulled it out and never had a probelm, no lights came on and the car still functioned. Never figured out what it was, kind of odd that it wasn't needed (hope it isn't an airbag sensor or something....) Mine was under the dash near the fuse panel.

I'm sure you're already familiar with this site: Nissan Altima Manual.

I'm definitely no expert when it comes to working on cars. However, given the operating sequence you report when operating the brake pedal, the following seems like a simple diagnostic to try that might help you narrow down the problem.

There are lots of diagrams. Many of them appear to be redundant. However this schematic seems to be somewhat applicable:

The stop lamp switch is connected to the fuse block through a 10A fuse #7.

When when the brake pedal is depressed, the switch opens and power is no longer fed to the Body Control Module. So, the default condition of the switch is closed, meaning that whenever the brake pedal is not depressed, a constant voltage is fed to the control module. This on/off state would seem to correspond to your experience with the high pitched electronic sound.

If you pull out fuse #7 and the sound stops, that may indicate you have a problem with the BCM. I'd say that probably means replacing it. However, I would suggest you consult with your mechanic before investing that kind of money in a new control board. Also if you do not replace this fuse after this test, you will not have brake lights.

It occurred to me that because of the two different locations in the travel of the brake pedal that silences the noise, it may be related to the cruise control system. A quick tap of the brake pedal deactivates the cruise control, however it remembers the last speed. Pressing "resume" reactivates cruise at the previously set speed. However, if the brake pedal is significantly depressed while in cruise mode, the cruise control erases the last stored speed and you have to perform the full setup again.

Hope this at least gives you something else to look at.

-dex

a reply to: Nyiah

Hi Nyiah,
It might help with the diagnosis if the guys are made aware that the inside of the car got soaked just before this?
(Sunroof was left open in a heavy downpour).
I'm not an expert, but I strongly suspect (due to the soaking) that there will be an electrical short-circuit somewhere inside the car, which is providing an earth-path (ground) for one or more of the many alarm buzzers on the car.
It may also be that the soaking has actually damaged an electrical component or circuit and that has triggered an alarm buzzer to sound?
The mechanic should be able to plug in a fault-code reader which will identify which circuit/component is at fault.

Good Luck!
G

a reply to: Gordi The Drummer

I'd wager it's unlikely. None of the electronics on the dash got wet, and the driver's side was bone dry. The passenger side seats & floors took the brunt of that. The passenger seat and rear seats aren't electronic in any way, the only seat that is is the driver's seat.
The fabric on the doors didn't even get wet, it all came in at just the right angle to run off the seat & to the floor (and fill the console) I'd entertain the possibility, if it weren't for a layer of pollen in the car from the last week (pollen's been a little ridiculous) that was completely undisturbed all over the dash & gauge shield. The pollen was only disturbed when I braced myself on the dash drying out the center console (which is essentially just a cup holder) I'd expect even rain splatter to disturb that and leave traces such as drip runs or droplet marks, but there is nothing.

I'll certainly give you credit for mentioning the impromptu interior bath, it wasn't even on the radar as a cause, but it doesn't seem like there's enough evidence. Nothing that was wet has any electric components.

To update, my husband said that when he hooked the battery back up overnight to close the windows & sunroof (rain came through again) that the noise did not occur that time. We can't figure that one out :/

a reply to: Nyiah

OK, cool - just seemed like too much of a co-incidence to me.

a reply to: Nyiah

Well, the nice thing is that if the moisture that reached the inside of the car is causing the problem, one it dries out, the problem will probably go away. That's a lot cheaper than having to replace one of the computer modules.

DC systems tend to be more forgiving of moisture incursion than AC systems once they have dried out.

Maybe that's why your husband didn't notice the problem last night.


-dex

Figured since you all were so helpful about this one that you'd appreciate an update from this morning's mechanic appointment.

Turns out the culprit was a simple loose wire related to the ABS system. At least it was just that and nothing more expensive to replace/fix! It's fixed now and the guy even tossed in a free oil change for the hell of it (he really had nothing to do this morning)