Alarm troubleshooting
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  1. #1
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    Alarm troubleshooting

    After a flurry of car repair/maintenance work last year, I took a break. I'm now trying to get back to solving my endless Alarm problem on my 99 Passat. I have no known water ingress, but I can't eliminate the possibility given the large number of passat owners that have had such problems.

    The alarm has been going off randomly for years . I can only avoid issues by locking the car without arming the alarm. Last year, the car was read with a VAG-COM and the only trigger was the hood sensor/switch. I identified a connector that went to the hood sensor, located near the front left headlight, and disconnected it. Unfortunately, the alarm continued to go off (if armed).

    Now I'm assuming the problem is either in the wire between the CCM and the hood connector, in the large connector at the CCM, or in the CCM itself. Prior to a few months ago, my bet was on the wiring because there were no other electrical problems. But recently, my sunroof has started to open randomly . I would have initially guessed that this may also be a CCM/wiring related problem, but I saw the thread about cleaning the electrical contacts on the sunroof switch. So the jury is out on the CCM.

    Anyway, before I rip the driver's side trim and carpet out and start troubleshooting the CCM harness, I wanted to see if anyone had any suggestions. I'm going to use a VAG-COM one last time to verify the hood is still the trigger. Also, if someone can provide a link to the CCM access instructions, I would appreciate it (I searched, but can't seem to find it).

    BTW, I haven't had a CEL in over a year because of all the help from everyone here! THANK YOU.
    Last edited by LineInTheWater; 05-13-2009 at 06:28 AM.

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  3. #2
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    I went ahead and started ripping things apart. I'm taking pictures along the way, in case anyone wants me to write up a "How to Access your CCM" tutorial (anyone interested?).

    I finally got to my CCM, and was able to pull it out from under the carpet (there is enough slack in the cable harness). My CCM is enclosed in a water (resistant?) black box. The wires, at first look, appear to be in very good condition. The connectors to the CCM (inside the watertight box) also look very good.

    Here is the pic:



    So now I need pinouts on these connectors. Anyone have these? Specifically, I need to know which connectors and which pins go to the hood sensor.

    *** IMPORTANT: Can I disconnect any of these connectors from the CCM?

  4. #3
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    OK, I found this on a another site. It clearly shows the pinouts for the two connectors on the CCM for the 99 Passat. I've highlighted the lines related to the hood switch. Does anyone know why the same wire appears to go to both the radio (lights) as the hood switch? This could have implications on my testing so far. Anyone? Also, it APPEARS that temporarily removing this wire from the connector would make it appear (to the CCM) that the hood switch (and possibly the radio?) is closed (and OK). Am I making sense here?


  5. #4
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    Looks like you've got a good start on things... Yes, you can disconnect that wire, I believe the hood switch closes to ground when it's open, same with the one built into the stock radio. A few thoughts, based on seeing issues crop up 'round here: I'd check the microswitch in the door lock mechanism for both the driver's and passenger's front doors - both the ones for door closure, and the ones for the lock open/ close sensing. They're a known failure point, and can set off the alarm. I'd also look at the factory made splices in the wiring harness between the CCM and up to the kick panel and dash area. Those can corrode and fail just from ambient moisture, even if you've not had any water intrusion issues. Also, check the ground (brown lead) in the kick panel area, possibly under the dead pedal, another known corrosion prone spot.

    As for your sunroof randomly opening, you most likely need to clean the contacts in the sunroof dial. It comes apart fairly easily, and you can use a pencil eraser to clean the contacts. Another relatively common issue on our cars...

  6. #5
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    soundguybob - As mentioned, the VAG-COM has always shown the trigger to be the hood switch. So, for now, that is where I'm concentrating. I'm going to double-check the triggers with the VAG-COM next week, just to be safe.

    Yes, I confirmed that the hood switch closes to ground when hood is open, and the switch is an open circuit when hood is closed. Based on the diagram above, it appears to me that the radio and hood are on the same wire - is this correct? Because this complicates matters. It means that the radio could also be causing the problem with an intermittent short to ground. Right?

    Can I safely disconnect the connectors from the CCM (in order to free the hood switch wire)? I don't need to disconnect the battery, do I?

    I will try to check the brown lead under the kick panel. Thanks.
    Last edited by LineInTheWater; 05-14-2009 at 08:11 AM.

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    Soundguybob - I see absolutely no corrosion, rust, fraying, etc of the wires in and around the CCM. Everything looks in good order, including the brown ground lead.

    Kinda feel like I'm talking to myself here. I've been doing a lot of searching and I have found other references to the radio and hood being on the same trigger wire. It is like the VW engineers ran out of inputs (8 max) and tied the two together. Nice design. So, instead of the the VAG-COM alarm codes indicating "hood contact switch", it should really indicate "Hood & Radio contact switch".

    I can't remember my factory radio ever being serviced (or removed to service something else). I do have a VAGUE memory of going to a stereo big-box electronics store like 7-8 years ago, and asking about a single-CD player. The tech came out to look at my car. Probably had nothing to do with it, but if my memory serves me, my alarm stopped consistently "chirping" (when armed) around that time. The intermittent alarm didn't start for a while after that.

    The radio may be a red herring. But I would really be kicking myself if my alarm hasn't worked for years because my radio wasn't seated properly. I just applied as much pressure to my radio as I could without breaking the plastic face. When I set the alarm, the car chirped - interesting, but not a good indicator, as mentioned.

    Does anyone have advice on removing the radio without "special tools"? I saw somewhere about using credit card strips to push down the sides and release the latches.

  8. #7
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    Update:

    I verified with multimeter that the radio trigger was directly connected to the hood sensor and CCM. So there is no doubt now. The schematic is accurate.

    I decided to permanently remove the input pin for the triggers at the CCM box. If this doesn't solve the problem, the only other culprit is the CCM itself. My fingers are crossed.

  9. #8
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    Another Update:

    Well, I expected to wake up in a panic - to the annoying "beep beep beep" of my alarm going off at 3am in the morning - fumbling to find the key in the dark and run to the window to disarm before my neighbors started yelling out their windows. BUT IT DIDN'T HAPPEN. I've had the alarm go this long before without triggering intermittently, but this is definitely a LONG time. It usually triggers within 5-15 minutes.

    Folks, I have several portions of writeups and pics, from last year and this post, that discuss troubleshooting the alarm (99 Passat and similar). I would be happy to put it all together and offer a comprehensive DIY. If anyone thinks this would be helpful, let me know.

    We'll see if my alarm holds up in the next few days.

  10. #9
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    No your not posting to yourself. Thanks for the posting and please let us know you finding in the next couple of days. We have been all over my car with alarm problems. To make a long story short we had intermittent problems with two sensors. The trunk sensor (would only trip under damp conditions mainly at night of course). Right rear door sensor would have never found it if we did not have to replace the door's mechanical lock.

  11. #10
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    BENCBEN - I also think the frequency of triggers was related to humidity and/or temperature. Maybe a bad solder joint or flaky connection somewhere between the CCM and the radio and/or hood (or maybe in the radio?). Hopefully not a bad solder joint inside the CCM!

    Another update: 24 hours and counting.... all quiet on the car-front. Have driven it today - rearmed the alarm several times. It will take me a week to believe this really worked.
    Last edited by LineInTheWater; 05-15-2009 at 01:50 PM.

  12. #11
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    I'm gonna bet that your issue was with the radio... glad you got it sorted out. A bad solder joint in the CCM would just cause the already open circuit to just be open, not close to ground, so at least in this case it's very unlikely that a bad solder joint would trigger the alarm...

  13. #12
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    Well, it has been 48 hours and NOT A PEEP from my alarm. Definitely the longest I've seen it go without triggering. I've made several trips with the car during this time .... had to stop myself halfway through my disarming procedure on multiple occasions. I'm almost at the point where I'm going to put everything back together. I think I'll give it a few more days (I know my luck).

    soundguybob - I'm guessing it is the radio too.

  14. #13
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    I'm declaring this fix a success!!

    I put everything back together this morning.

    It only took 7 years for the fix.

  15. #14
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    If only I'd done a search and read this post last night...

    My alarm stopped "honking on arm" so I took a peek at things via vag-com and the hood switch showed up as the culprit. I dismantled the hood latch and messed around with the micro switch with no results. Then I figured, the switch is 10 years old and must have failed, so I clipped it out and connected the wires together as a bypass until I could get a replacement. To my surprise, vag-com still shows the hood open (with that circuit open or closed)! Then it got dark out so I tabled further work till the next day.

    The first thing I did today was what I should have done before I clipped out the switch. I did a search on PW. So... the radio is also on that "zone" of the alarm. I'll bet thats where my problem is.

    LineInTheWater, thanks for the info. I bet I'll find the problem in no time now.

  16. #15
    Moderate Moderator Steve in Chicago's Avatar
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    Update: Replaced the hood latch sensor switch and re-seated the radio in the dash. Alarm went back to "honk-on arm".

    For anyone about to replace the hood latch switch, route the new switch harness along the same path the original harness used. I used additional zip ties to insure the cables along that run will stay out of the fan.

  17. #16
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    UPDATE: It has been about five months and .... MY ALARM STILL WORKS!!


    Steve_in_Chicago - glad my thread helped you out! Glad to see I'm paying back some of the great help I've received by others on this forum.

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    LineInTheWater. Really nice post. I have not had the pleasure of trying to fix my alarm issues yet. But it is next on my list of todos and wanted to know if you may have finished the DIY you mentioned making. I'm repairing the CCM wire harnesses tomorrow morning and I could use some help with this alarm.

  19. #18
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    Quote Originally Posted by Jim_S View Post
    LineInTheWater. Really nice post. I have not had the pleasure of trying to fix my alarm issues yet. But it is next on my list of todos and wanted to know if you may have finished the DIY you mentioned making. I'm repairing the CCM wire harnesses tomorrow morning and I could use some help with this alarm.
    Jim - I never received any feedback on a comprehensive DIY ... so I put it on the back burner. I have a DIY to get to the CCM (with pics) ... and I'd be happy to walk you through the other steps to troubleshooting the alarm. Let me know what I can do to help!

  20. #19
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    Having had this problem myself, I completely agree with the others who mentioned the stereo.

    As confirmed, the stereo shares the same analog security zone as the hood. (You could use this analog zone to wire in motion sensors and stuff if you know what you're doing...)

    If the OEM stereo is not seated correcty, it can randomly trigger the alarm and/or prevent the alarm from chirping on arm.

    It's happened to me twice. Each time, removing and reseating the OEM stereo fixed the problem.

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