Alarm Malfunction Mystery

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by echase, Jun 8, 2009.

  1. echase

    echase New Member

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    I'm totally stumped, but I'm, not a Prius tech, I don't even play one on TV (or the internet). My prius seems to have become possessed this evening. Perhaps poltergeist, or that thing from the movie "pulse"

    Here's the relevant info, perhaps brighter minds will prevail where I have failed:

    My 08 Pkg 1 started sounding alarm at semi-random intervals late tonight while parked in my garage. Here's my troubleshooting so far:

    1. Survey area, interior of vehicle, no intruders, animals, large insects. Problem recurred in ~20minutes. :cool:

    2. Open/close all doors, hood and hatch. Power cycle vehicle. Problem recurred in about 1/2 hour. :confused:

    3. Google "prius alarm problem". Remove plastic sunglasses from sunglasses tray. Problem recurs while walking away from vehicle.

    4. Leave drivers side door open, wanting sleep, willing to risk discharging 12v battery. Problem recurs in about 5 minutes. (What the heck!?... the door was OPEN, how does the alarm go off in this state) :eek:

    3. Remove battery from FOB to rule out malfunctioning panic button. While opening the fob the problem recurs a few times! I'm thinking must have been the panic button. Problem recurs in less than 5 minutes. :eek:

    4. Fumble around the low voltage battery trying to figure out how to unhook the darn thing. Alarm goes off many times during this process, thinking bad battery contact? Can't figure out how to unhook the darn thing. :confused::confused:

    5. Fumble around fuse box looking for a large main fuse of some sort. Can't find one. Alarm goes off in my face a few times. Ears still ringing. (And it sounds so wimpy from the cabin.) Waiting for sleepless neighbors to start using colorful language. :mad:

    6. Wife recommends leaving key in ignition. Alarm shuts up. :cheer2:

    Also, ran the internal diagnostic to check low-voltage battery charge. It displays 12.4 with minimal load, 12.1 with AC running in "ON" mode. When powered on to "READY" it displays 14.5 volts, which seems a little high for charging, but I could be wrong. Like I said, I don't know a lot about this stuff, but I'm fairly handy with Google.

    Any Ideas?
    :confused::(:confused:
     
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Does your Prius have an aftermarket alarm installed? I haven't heard that the factory alarm has a problem with false triggering.

    If you wish to disconnect the 12V battery for temporary relief, the easiest way to do that would be to remove the negative terminal connector where it bolts into the body. This assumes that you have a metric socket of the correct size (probably 10 mm).

    An alternate disconnection method is within the main relay/fuse box near the inverter. You would have to remove the nut below the red cover of the dedicated positive jump start terminal, and take the positive cable off the stud. Then close the cover so the cable cannot contact the stud.

    The 120A MAIN fuse is located within the 12V battery red positive terminal. When the red cover is removed, the fuse is visible in the fuse block below the cover. However it probably would be easier to disconnect the negative terminal as described above.

    Sounds like a dealer visit is in order, after you've caught up on your sleep. Good luck.
     
  3. dogfriend

    dogfriend Human - Animal Hybrid

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    I was going to suggest a loose ground wire at the 12v battery. Either that or the 12v battery in its death throws.
     
  4. echase

    echase New Member

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    The car is eight months and 7,000 miles old, seems premature for 12V end-of-life. Also clock keeps correct time, which to me indicated contact had been maintained.

    Alarm is original, without breakage sensors.
     
  5. dogfriend

    dogfriend Human - Animal Hybrid

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    I agree, but it isn't impossible - batteries can have internal defects - I had a battery fail after about one year in another vehicle because the installer hammered the battery terminal onto the post and cracked it internally.

    My suggestions come from the previous observation that alarm systems tend to go nuts when the proper voltage is not maintained and / or the voltage drops intermittently.

    I would check that ground wire from the 12v battery to the car body to make sure the connections are tight.
     
  6. echase

    echase New Member

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    Will do!

    I take it that the observation of normal voltage according to the onboard diagnostics does not rule out a bad battery? Also, the clock is keeping time, but perhaps it has a backup power source for minor interference.

    Wierd. The problem did not recur for several hour this morning. We'll see about tonight.
     
  7. echase

    echase New Member

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    So far the Prius has been sleeping soundly. Perhaps the hybrid gods have been appeased?
     
  8. dogfriend

    dogfriend Human - Animal Hybrid

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    Or your neighbors figured out how to silence it permanently. :madgrin: :D
     
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