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VW MKV-A5 Golf/Jettas Discussions area for A5/MkV Jetta/Golf (2005/2006 PD and 2009 CR).

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Old October 20th, 2012, 15:31   #1
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Location: Las Vegas, Nevada
Default Mk5 OBDII port and electrical system

I will start with my question and then explain why I ask it.

Question: Does the Mk5 OBDII port have a pin that is un-switched 12v power? In other words, is there a pin where the power does not go off when you turn off the key? (I thought about posting this in the OBDII scanners forum, but this is really not about scanners)

And now (as Paul Harvey used to say) - the rest of the story.

This morning I had to jump start my car. The battery was discharged (weak). There are two things new in my car. The first new thing is the battery, and the second new thing is a P3Cars Digital Interface (boost and EGT gauge). When I turn off the car the EGT gauge stays on for a few seconds and then goes off, so I know it doesn't go off immediately with the ignition. Something is apparently slowly draining my battery, and I surmise that it is one of three things:

1) My new battery is faulty
2) My P3Cars Digital Interface is slowly draining my battery
3) Something else is slowly draining my battery (a new problem)

I currently have a charger on my battery. My plan is to start unplugging the P3Cars device when I am not driving (it just plugs into the OBDII port) and see how the battery holds a charge. I am just curious if it is possible for a device plugged into the OBDII port can actually drain the battery when the car is turned off.


2009 Jetta SportWagen TDI (gone but not forgotten)
2018 VW Tiguan SE (I wish it was a TDI)
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Old October 21st, 2012, 13:24   #2
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Old October 21st, 2012, 18:54   #3
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Default Update (in case anybody cares)

Update (in case anybody cares)

What I have learned so far.

It is not items 1 or 2 (in first post)

I left the P3Cars Digital Interface unplugged and the battery still drained and failed to start without a recharge (this eliminates #2).

I went to the place where I bought the battery and they spent about an hour testing my charging system (all good) and load testing the battery (also good). This pretty much eliminates #1 as the cause

This leaves option #3 (something else is slowly draining my battery). I did a VCDS autoscan and found several new fault codes. One was a CAN gateway fault about no communications with telephone. The others were faults from electric window motors that said "No or Incorrect Basic Setting / Adaptation - Intermittent". I got this fault from both the driver's door and the right rear door. I also got a fault from the radio that said "Databus for Infotainment 014 - Defective - intermittent". I am going to ask the guys at Ross-Tech if any of these faults could keep some controllers from properly "going to sleep".

All of these faults were cleared and they have not come back (at least not yet). We shall see what happens tomorrow. I wanted to verify "sleep state current" (as per TSB 27 08 04), but I could not find a current measuring clamp that would work. Therefore we will play the "wait and see" game for another day. I have a stand alone jump start battery fully charged and in my car in case I need it.

Have Fun!

2009 Jetta SportWagen TDI (gone but not forgotten)
2018 VW Tiguan SE (I wish it was a TDI)
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Old October 21st, 2012, 20:15   #4
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TDI(s): 2010 jetta
Fuel Economy: best tank 50.6, worst 36

Don I think its your electric personality draining the battery. your need to swap poles so you charge the battery instead.
2010 jetta, 6sp man, & tdiclub plate frame ..build date 08-09
1956 Buick Special (my dad bought it brand new)
1946 Luscombe 8E
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