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Alarm system compromise illuminates check engine light?

Discussion in 'Technical Q&A' started by ActionFigure, Jul 6, 2010.

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  1. ActionFigure

    ActionFigure Formula Junior

    Sep 2, 2005
    440
    Cary NC
    Full Name:
    Matt
    #1 ActionFigure, Jul 6, 2010
    So here is something of a head scratcher. I am driving my 98 355 spider in downtown Raleigh and am going about 30 mph and am about 20 minutes into my drive. The check engine light comes on. I take the car to my mechanic and the only fault his OBD reader is getting from the ECU is that the alarm system was compromised, or something to that effect. Basically it is reporting that someone tried to access the car while it was locked and the event was recorded in the ECU. The really odd thing is that I hardly ever lock my doors as the top is always down anyway, so there was no attempted access while the car was locked AND the fault illuminated the check engine light which is something it should have never done, it should have just been a recorded event AND it happened while I was driving my car with the doors unlocked (and moving at 30 mph makes it a challenge for anyone to try to break into the car anyway). When he acknowledged the fault in the ECU with his reader the check engine light went out. That was the only fault in the ECU. So, maybe as I was driving along someone else was unlocking their car with a fob that was close in frequency to mine that my car "heard" and thought that someone was trying to breech the security system while we were moving and that really wigged out the ECU and it lit the check engine light? Has anyone ever seen this behavior and figured out why it tripped the light? Was it just my car being cranky and getting even with me for driving it in 95 degree heat?
     
  2. windsock

    windsock Formula 3
    Rossa Subscribed

    Nov 29, 2006
    1,162
    #2 windsock, Jul 6, 2010
    Last edited: Jul 6, 2010
    Alarm system did not cause your check engine light. likely the aftermarket code reader is not retrieving all the codes or providing a incorrect definition. Resetting the errors likely cleared whatever error was present. What was the actual error code? It will likely return if nothing has been addressed. best of luck
     
  3. ActionFigure

    ActionFigure Formula Junior

    Sep 2, 2005
    440
    Cary NC
    Full Name:
    Matt
    #3 ActionFigure, Jul 6, 2010
    Sorry, I should have been more specific. It wasn't an OBD II reader that just grabs and displays a numeric code so and you can clear it. It has the software that works in real time with the ECU so that you can read voltages, mixture, etc. It did not generate a code, it specifically spelled out the verbage for an alarm system compromise which when specifically cleared turned off the check engine light. Yea, weird.... I know.
     
  4. tazandjan

    tazandjan Three Time F1 World Champ
    Lifetime Rossa Owner

    Jul 19, 2008
    39,318
    Clarksville, Tennessee
    Full Name:
    Terry H Phillips
    #4 tazandjan, Jul 6, 2010
    Matt- A generic reader like that is not getting any read-outs from the Alarm ECU and the Alarm ECU will not illuminate a CEL. You need an SD1 or SD2 to see that kind of information, or at least an ST-05.

    Your car has the same Alarm ECU as the 456s and 550. None of them will illuminate a CEL light. Your Alarm ECU has the ID and a rolling code memorized for each of your remote fobs. The odds of any other fob having something the ECU would recognize are virtually nil. There are lots of 315 Mhz signals out there, but none are going to get into your Alarm ECU, and even if they did, you would not get a CEL. Signals you get from the Alarm ECU are series of beeps from the siren and flashes on the LED, all of which should be explained in your Alarm Manual.

    http://www.ricambiamerica.com/product_info.php?products_id=280987

    Taz
    Terry Phillips
     
  5. windsock

    windsock Formula 3
    Rossa Subscribed

    Nov 29, 2006
    1,162
    #5 windsock, Jul 7, 2010
    Whatever you are using retrieves the error from the motronic unit, as an numerical error, based on the numerical error your scanner laptop provides a definition from a internal definition table. I suspect the definition in your table is wrong or you retrieved an error for the immobilizer being active which is a common error and will be stored if you attempted to start the car without dissarming the alarm, a common occurance. This is not what turned your check engine light on.
     
  6. f355spider

    f355spider F1 World Champ
    Owner Rossa Subscribed

    May 29, 2001
    18,055
    USA
    #6 f355spider, Jul 7, 2010
    Sounds like the next step is to post the actual code your scanner was reading, and we can try and decipher it for you. I have a list...the file is to large to post here as an attachment. Email me and I can send it to you.
     
  7. ActionFigure

    ActionFigure Formula Junior

    Sep 2, 2005
    440
    Cary NC
    Full Name:
    Matt
    #7 ActionFigure, Jul 7, 2010
    Sorry, there is no code generated to pass on since the interface to the ECU that was used was an ST5 (here is a link for this USD $15,000 item for clarification: http://www.rockboundrovers.com/catalog_3.html). The thing interfaces with software in real time so there is no code to cross reference, it verbally tells you what is in the ECU. I hope this helps, sorry that I was not clearer in the beginning as it would have avoided the confusion about codes and such and kept the thread a bit neater. I hope this helps and thanks for the suggestions.
     
  8. f355spider

    f355spider F1 World Champ
    Owner Rossa Subscribed

    May 29, 2001
    18,055
    USA
    #8 f355spider, Jul 7, 2010
    Matt, as others stated, if the CE light was illuminated, there should be a "P" or diagnostic code stored. The alarm cannot trip the CE light.
     
  9. tazandjan

    tazandjan Three Time F1 World Champ
    Lifetime Rossa Owner

    Jul 19, 2008
    39,318
    Clarksville, Tennessee
    Full Name:
    Terry H Phillips
    #9 tazandjan, Jul 7, 2010
    Last edited by a moderator: Sep 7, 2017
    Matt- The ST05 will read codes stored in the Motronic ECU. It has some of the functionality of the SD2, which will do the same thing. Unlike the SD2, though, the ST05 does not interface with all the ECUs including Alarm ECUs. Here is a list of what the ST05 can do for your car.

    Taz
    Terry Phillips
    Image Unavailable, Please Login
     
  10. lndshrk

    lndshrk Formula Junior

    Nov 7, 2003
    753
    SLC, Utah
    Full Name:
    Jim Conforti
    #10 lndshrk, Jul 8, 2010
    The illumination of a check engine lamp, more correctly referred to as a MIL (malfunction
    indicator lamp) only occurs when an emissions-relevant fault is detected by an emissions
    ecu (engine or transmission mostly).

    If the MIL illuminates there will most certainly be a code stored within the ecu.
     

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