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Thread: VW 2005 mk4 Jetta - Hood Latch Question

  1. #11
    Verified VCDS User Zenerdiode's Avatar
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    ...and that's at the connector near to the headlight? Does it look clean, without corrosion? Photo?

    If so, your next port of call is the connection to J393 - at T15/1. If you can, use a back-probe and get a connection to the terminal in chamber 1. Test its voltage with respect to ground. Short it to ground whilst viewing VCDS MVB. Unplug the 15-pin connector, test from terminal 1 (T15/1) and T2a/2 on resistance.
    Last edited by Zenerdiode; 08-12-2019 at 02:14 AM.

  2. #12
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    Hi Zenerdiode, to answer your qeustion, yes it is the hood latch switch connector plug near (in my case) passenger side (right) headlight. See photo:



    With it unplugged you can see the spade terminals appear to be without corrosion, no green corrosive stuff you had mentioned earlier. See picture:



    Corrosion was one of my first thoughts, so I actually de-pinned the signal wire (brown/red) to inspect the crimped spade connector and all looked good, very nice clean connection. I actually did not do the same however for the ground (brown) wire. I will do that next. High resistance from this wire to ground makes me think maybe bad ground connection in the headlight harness where it tries to find ground, or the wire itself is compromised?

    Before I go tearing the front dash apart to find J393 (this will have to wait until at least next weekend), would it be appropriate to simply add a new ground using a wire tap off of the brown T2a/1 wire to a chassis point in that location? I know this is not the "proper" fix, but is this a logical approach?

    lastly, not sure what you mean by a "Back-probe" ? Thanks again

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  4. #13
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    Actually, thinking about it more, adding a new ground from a wire tap off of brown T2a/1 wire would not help the situation, as I still do not have voltage present at the T2a/2 pin....correct? Its a mute point to fix the ground when I do not have the voltage I should have coming in...

  5. #14
    Verified VCDS User Zenerdiode's Avatar
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    Ah, thank you for posting the pictures; they are indeed worth a thousand words.

    Yep, ~5Ω is a little high, but we know that doesn't need addressing yet, as shorting T2a/2 directly to ground isn't toggling the indication.

    Back-probing is where a connector remains connected to its receptacle; (so all other power, ground, sensor and actuator wires remain connected) and a thin probe is passed into the connector to the pin under test, from the back of the connector. I appreciate it is not always possible with the style of wire seals on some connectors in harsh environments, but with J393 being inside the cabin, it maybe just possible.

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    Hi Zenerdiode,
    Okay I now understand what "back-probing" is. I was actually wondering that this morning how I am I supposed to test T15/1 voltage at J393 with respect to ground with it still plugged in....now it makes sense! I will order a "back probe kit" from good ole trusty Amazon.

    So hopefully this weekend I will perform the next logical tests to trouble shoot this issue:
    1) Test T15/1 voltage with respect to ground. What should I expect to see in the measuring block whilst shorting it to ground?
    2) Unplug 15 pin connector and confirm signal wire continuity by measuring resistance from terminal 1 (T15/1) to T2a/2

    Will report back! Thanks again!

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    Also, could anyone shine a bit more detail as to what the physical connection point of "B161 - Connector (anti-theft warning system) in wiring harness interior" is....looks like.....location....? This Saturday, I plan to first backprobe T15/1 at J393, if I do get voltage there with respect to ground, my next thought is there is something going on with this "B161" connector.... as I believe (will confirm) I have voltage at T8/1 on the radio 8 pin connector. Thanks!

  9. #17
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    ^^^^rbb1485: I know nothing about the mk4 Jetta, but I am enjoying (in a perversely voyeuristic way) reading your unfolding story with zenerdiode. It's a kind-of master-class in fault diagnosis - very well done indeed!!!

    Anyhow - enough of the hagiography (as the saying goes) - with my opening comment as a caveat (i.e. my ignorance in matters Jetta related), here's an extract that might shed some light on your question



    If I read your WD correctly, B161 looks like one of these "welded connections" - I think. As to where this little beastie is in the car's wiring loom - I'll leave that answer to someone who actually knows the car intimately!!

    Don
    VW Golf MkVII (MY13) - A3 8V hatch (MY17)

  10. #18
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    The exact location of those points is not given in the wiring diagrams unfortunately, only the general location (dashboard wiring loom or interior wiring loom for example).
    Current:
    2018 Tiguan AD Highline 2.0 BiTDI 240hp > Stage 1+ 328hp
    2016 Polo 6C Highline 1.0 TSI 105hp

  11. #19
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    Hi all, thanks for the feedback! Well on to the next troubleshoot tests results:
    1) Test T15/1 voltage with respect to ground --> Using my new "back probes" i was able to measure voltage at T15/5 (oddly enough the red/brown wire was in terminal 5 location, not 1 as the WD shown) and i got 0.01V, and the MBV of the hood switch F120 showed "OPEN" the entire time......confirmed I had a good ground by testing another terminal and got 12V.

    2) Unplug 15 pin connector and confirm signal wire continuity by measuring resistance from terminal 1 (T15/1) to T2a/2 --> The resistance dropped to nearly 0ohms (~0.5ohm) so I believe the 0.5mm red/brown signal wire is intact and OK

    I then removed the CCM entirely from the vehicle, and opened it up to inspect for any water damage, corrosion, and oddly enough it looked very clean, all good solder joints, etc. Below are the actual photos:





    So I guess my next step is to match a used CCM from a wagon and picked one up from ebay or something, any other thoughts? Thanks again

  12. #20
    Ross-Tech Employee Dana's Avatar
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    Make sure that Radio is fully seated/locked into the dash. If memory serves one of the locks on the right side is directly tied to the switch that powers your hood latch switch.

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