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Thread: Battery Testing using VCDS

  1. #1
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    Battery Testing using VCDS

    As a result of trying to determine the cause of my handbrake/auto hold issues I have been looking at the battery voltage. I unnderstand that the electronic handbrake circuits are sensitive to battery voltage.
    During my auto scans using VCDS, the battery voltage is reported as being 11.9-12V. VCDS battery testing shows the state of charge to be 70%.
    My question is this- does VCDS report the actual voltage reading at the battery terminals, or does the voltage get regulated somewhere in the car to a nominal 12V and this is what is reported?
    Car is nearly three years old with an AGM type battery, which was fully charged using a CEK 5.0 Smart charger about a month ago.
    Last edited by niggly60; 05-19-2019 at 02:59 AM.

  2. #2
    Verified VCDS User Zenerdiode's Avatar
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    Quote Originally Posted by niggly60 View Post
    Car is...
    What model?

    Depending on what interface you use; the 'VBatt start/end:...' at the end of an Auto-Scan is what the interface measures itself at the DLC. There may be some volt drop over the fuse and wiring from the battery, through the fuse panel to the DLC. Other voltages that may be monitored in Measuring Values or Freeze Frame data of individual modules - are that individual module's interpretation/measurement of voltage. By the very nature of electrical principles, if the module is a heavy consumer of power, its reported battery voltage may indeed be different to other modules.

    The CTEK 5.0 is a fantastic charger (I have one myself) however, because its output is only 5A (and modulated to de-sulphate battery plates etc.) you need a different device if you are maintaining your electronic handbrake. I'm only guessing - as I don't know hat kind of car you have - but you'll probably need something in the order of a 20A continuous output if doing brakes.

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  4. #3
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    Thanks for your reply zenerdiode.
    In response to your questions- my car is a 2017 VW Tiguan Mk 2 4WD 2.0L diesel.
    I have had issues with the handbrake and auto hold not releasing on occasions- each episode lasting a week or so, with no apparent set of circumstances indicating a cause.
    My dealer finds nothing on test and indeed- the car behaves when it goes in to be checked!
    So I purchased a VCDS cable etc. with the hope of finding an underlying cause. My latest theory relates to battery voltage and this is what I was looking into with VCDS.
    About a month ago I measured the voltage across the battery with a multimeter and it read 12.4V
    I then charged it for about 5 hours with the CTEK until it got to stage 7. The brakes have again been playing up and that is when I went into VCDS and it told me the battery was at 70% charge with a voltage of 12.0 shown at the end of my Autoscan.
    Do you know if it is possible to do some more involved testing of voltage levels- perhaps within the ABS controller?

    UPDATE: Just measured battery standing voltage with a multimeter and it's 12.2V Engine running 14.8V
    Last edited by niggly60; 05-19-2019 at 06:56 AM.

  5. #4
    Benevolent Dictator Uwe's Avatar
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    For continuity, reference this thread:
    https://forums.ross-tech.com/showthread.php?18510

    In order to accurately assess a battery's state of-charge based on its voltage, you have to measure its voltage directly at its terminals while there is no load on the battery at all, and preferably after that battery has been "at rest" (with no load or charge applied) for an hour or two.

    VCDS can't really do that. The voltage VCDS shows will generally be lower than the actual battery voltage due to the voltage drop in the wiring, fuses, relays, and such between the battery and the DLC (or module). In addition the battery itself has an internal resistance, which will drop the voltage at its terminals more-or-less proportionally to the load on the battery at any given moment.

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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    Thanks Uwe.
    I have just measured the battery terminal voltage after the car has been sat overnight- 12.2V ; It was 14.8V with the engine running. Given the battery was fully charged about a month ago and I have no extra equipment added, it does seem to be a bit low.

  7. #6
    Benevolent Dictator Uwe's Avatar
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    14.8V with the car running is not "battery voltage" but "alternator voltage".

    I agree the if the car was shut down overnight, and there were no loads applied, 12.2V seems low; that's approximately 60% SoC, maybe a bit less. Is it safe to assume that you're measuring this with a meter, directly at the battery?

    What kind of driving does this vehicle see during a typical day?

    I would also try to measure the battery voltage before you go to bed, and then again the next morning, to see if perhaps there's an undue drop indicating an excessive drain from the car.

    Lastly, pull the battery History data and post it here.
    [Applications]
    [History Data]
    http://www.ross-tech.com/vcds/tour/history-data.php

    -Uwe-
    The engineering problems are likely insurmountable. It would be like proposing to land a rocket booster section on a barge floating in the middle of the ocean.

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  9. #7
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    Yes, that was with a multimeter, across the battery terminals.
    My typical daily commute is 10 miles each way- a mix of urban and motorway driving. Heated seats and screens are not used that often.
    I will investigate the battery history data and get back to you.
    Thanks again.

  10. #8
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    Battery history file:

    Code:
    ;;Sunday,19,May,2019,14:53:46:03359
    ;                Address 19: CAN Gateway
    ;Control Module Part Number: 5Q0 907 530 AM
    ;  Component and/or Version: GW MQB High   128 1265
    ;           Software Coding: 030500041F087300FB07225E0A0F00010001050000000000000000000000
    ;            Work Shop Code: WSC 01357
    ;                      VCID: 7CA00149866BB617C25-8028
    ;
    ;History Data
    
    Record 1/16: No-load voltage underranging
    2019-05-19-14:50*01.0*03*00782***
    2019-05-19-12:48*14.6*03**
    2019-05-13-15:22*00.0*03**
    -------------:--*--.-*--*-----***
    -------------:--*--.-*--**
    -------------:--*--.-*--**
    -------------:--*--.-*--*-----***
    -------------:--*--.-*--**
    -------------:--*--.-*--**
    
    Record 2/16: No-load current overranging
    -------------:--*---*---*--.---*-------------*-*--*-----**
    -------------:--*---*---*--.---*-------------*-*--**
    -------------:--*---*---*--.---*-------------*-*--**
    -------------:--*---*---*--.---*-------------*-*--**
    -------------:--*---*---*--.---*-------------*-*--**
    
    Record 3/16: Shut-off stage history
    2016-09-19-18:05*T*0*089*055*0-0-0-0-1-0-0*_*0*00.0*00.0**
    2016-09-15-17:00*T*0*088*056*0-0-0-0-1-0-0*_*0*00.0*00.0**
    2016-09-15-13:23*T*0*088*056*0-0-0-0-1-0-0*_*0*00.0*00.0**
    2016-09-14-17:22*T*0*089*057*0-0-0-0-1-0-0*_*0*00.0*00.0**
    2016-09-11-07:24*T*0*092*058*0-0-0-0-0-0-0*_*0*00.0*00.0**
    2016-09-09-11:19*T*0*091*057*0-0-0-0-0-0-0*_*0*00.0*00.0**
    2016-09-08-08:01*T*0*091*055*0-0-0-0-0-0-0*_*0*00.0*00.0**
    2016-09-06-15:51*T*0*088*056*0-0-0-0-0-0-0*_*0*00.0*00.0**
    2016-09-06-15:13*T*0*091*060*0-0-0-0-1-0-0*_*0*00.0*00.0**
    2016-09-05-14:06*T*0*089*058*0-0-0-0-0-0-0*_*0*00.0*00.0**
    
    Record 4/16: Battery change history
    2016-09-01-00:04*03*068*JCB*1111111111*09986*03995*0000*0000*0000**
           0000000km*02*068*JCB*1111111111*10000*00004*0000*0000*0000**
           0000000km*01*068*JCB*1111111111*09999*00000*0000*0000*0000**
    
    Record 5/16: Energy-critical vehicle states
    -------------:--*-*--.---*--.--*---*--*---.-*-----*-----*------*-------------*-*-*-*--.-*--.-*---.-*--*--*--*--*--**
    -------------:--*-*--.---*--.--*---*--*---.-*-----*-----*------*-------------*-*-*-*--.-*--.-*---.-*--*--*--*--*--**
    -------------:--*-*--.---*--.--*---*--*---.-*-----*-----*------*-------------*-*-*-*--.-*--.-*---.-*--*--*--*--*--**
    
    Record 6/16: Energy balances (last 10 trips)
    2019-05-19-12:51*031*+18*+000.3*00.00*0.00*000**
    2019-05-18-14:40*037*+30*+000.3*00.10*0.00*000**
    2019-05-18-14:02*038*+28*+000.5*00.20*0.00*000**
    2019-05-18-12:58*037*+25*+000.4*00.10*0.00*000**
    2019-05-18-11:56*037*+22*+000.4*00.30*0.01*000**
    2019-05-18-10:56*037*+19*+000.3*00.20*0.01*000**
    2019-05-18-10:20*038*+18*+000.3*00.10*0.00*000**
    2019-05-18-10:14*039*+18*+000.1*00.00*0.00*000**
    2019-05-17-18:39*038*+28*+000.5*00.10*0.00*000**
    2019-05-17-18:07*038*+28*+000.7*00.10*0.01*000**
    
    Record 7/16: Energy balances (last 10 standing times)
    2019-05-18-14:46*031*+006.3*022.0*00.3*00.2**
    2019-05-18-14:15*037*+000.2*000.3*00.0*00.0**
    2019-05-18-13:10*037*+000.2*000.8*00.0*00.0**
    2019-05-18-12:14*037*+000.2*000.7*00.0*00.0**
    2019-05-18-11:09*037*+000.2*000.7*00.0*00.0**
    2019-05-18-10:30*036*+000.3*000.3*00.0*00.0**
    2019-05-18-10:18*037*+000.2*000.0*00.0*00.0**
    2019-05-17-18:48*039*+000.3*015.5*00.0*00.0**
    2019-05-17-18:16*038*+000.2*000.3*00.0*00.0**
    2019-05-17-12:51*037*+000.3*005.2*00.0*00.0**
    
    Record 8/16: Battery manipulation (e.g. charging)
    2019-05-18-10:15*4*04*00*00*99*2019-05-17-18:49*03**
    2019-05-17-18:07*4*04*00*00*99*2019-05-17-13:09*03**
    2019-05-17-11:20*4*04*00*00*99*2019-05-17-06:37*03**
    
    Record 9/16: Battery aging
    2016-09-02-00:47*100*100*100*054*00000*12.80*+22*02*03*12.70*00000*00000**
    2020-09-29-16:05*100*092*074*041*02697*12.40*+23*04*03*03.05*00221*01103**
    2018-05-16-16:05*091*091*078*039*02601*12.50*+23*04*03*03.15*00211*01056**
    2018-04-18-16:05*100*090*076*041*02456*12.50*+23*04*03*03.10*00200*00998**
    2018-03-21-16:05*093*091*090*046*02264*12.70*+16*04*03*03.20*00187*00911**
    2018-02-21-16:04*094*093*088*044*02144*12.60*+13*04*03*03.20*00175*00852**
    2018-01-24-15:32*093*094*080*037*02067*12.50*+12*04*03*03.10*00169*00826**
    2017-12-27-13:31*095*093*087*039*01993*12.60*+02*04*03*03.15*00163*00800**
    2017-11-28-16:05*093*092*080*039*01924*12.50*+14*04*03*03.20*00154*00755**
    2017-10-31-16:04*094*094*077*039*01835*12.50*+19*04*03*03.20*00141*00696**
    2017-10-03-16:03*094*094*076*039*01717*12.50*+22*04*03*03.10*00130*00645**
    2017-09-05-16:03*100*093*083*046*01547*12.60*+24*04*03*03.15*00113*00549**
    
    Record 10/16: Dynamic energy management
    -------------:--*-*---.-*-----*-*---.-*-----*--.--*-------**
    -------------:--*--*--.-*--.--*---.-**
    
    Record 11/16: Recuperation
    2019-05-18-14:46*000*000*000*006*0035*006*00.1*00.4*074*037*075*037*01*00588*00827*01483*01481*04841**
    2019-05-18-14:15*000*000*000*013*0123*013*00.1*00.7*074*037*075*038*01**
    2019-05-18-13:10*000*000*000*010*0085*011*00.1*00.6*075*037*076*037*02**
    2019-05-18-12:14*000*000*000*017*0160*018*00.2*00.9*075*037*076*037*02**
    2019-05-18-11:09*000*000*000*012*0118*013*00.3*01.0*076*036*076*037*03**
    
    Record 12/16: Start-Stop
    2018-03-01-15:39*1-0-0-0-0-0-0-0**
    2018-03-01-15:20*1-0-0-0-0-0-0-0**
    2018-03-01-15:15*1-0-0-0-0-0-0-0**
    2018-03-01-15:14*1-0-0-0-0-0-0-0**
    -------------:--*---------------**
    00004*00000*00000*00000*00000*00000*00000*00000**
    -------------:--*---------------**
    -------------:--*---------------**
    -------------:--*---------------**
    -------------:--*---------------**
    -------------:--*---------------**
    -----*-----*-----*-----*-----*-----*-----*-----**
    2018-09-10-08:32*2*059*024*+21*04*025*+29.95*14.7*1**
    2018-06-01-14:43*2*059*026*+23*04*025*-32.67*11.9*0**
    2017-09-07-10:29*2*054*020*+27*04*025*-99.99*10.6*1**
    2017-04-21-13:08*2*056*020*+18*04*025*-31.85*11.7*0**
    2017-04-13-07:45*2*058*024*+19*04*025*-19.53*11.9*0**
    00000*00007*00000**
    
    Record 13/16: Sporadic alternator faults
    -------------:--*---------*---.-*-----**
    -------------:--*---------*---.-**
    -------------:--*---------*---.-**
    
    Record 16/16: Vehicle energy balance
           0038760km**
    00396*01919*01641*00008*00000**
    08723*00282*00092*00014**
    16983*01120*00001*00000**
    00972*01281*00167*01293**
    02144*01272*00296**
    00000*00000*00000*00000**
    00000*00000*00000*00000**
    00102*00011*00002**
    00009*00001*00001**
    00002*00000*00000**
    00164*00195*00206*00200*00181*00119*00203*00149*00108*00193*00000**

  11. #9
    Verified VCDS User Zenerdiode's Avatar
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    Quote Originally Posted by Uwe View Post
    For continuity, reference this thread:
    https://forums.ross-tech.com/showthread.php?18510
    Sorry Nigel, didn't see your other thread. Thanks Uwe. Again, forgive my ignorance, but I don't know where the battery is housed on your Tiguan. (In the boot or under the bonnet?) However, either way, when you open either, you will 'wake-up' some of the systems in the car. In my own experimentation I found the BCM2 could pull nearly 15A just by opening the door; however the car gets very frugal with power (drawing the order of a few mA) when it goes to sleep properly.

    So what I'm saying is; in addition to Uwe's suggestion above, if your battery is in the engine compartment, leave the bonnet open but click the latch to ensure the car goes to sleep properly when you leave it overnight. Obviously the same with the boot - if it's in there. You need to set the alarm and lock it with the apertures open so you don't wake it and start consuming current when you go to measure the next morning.

    Hill-hold and the EPB look for an engine torque value from the ECM on the CAN bus. They also require the seatbelt to be fastened. Don't rule out having a dodgy microswitch on your belt buckle...

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  13. #10
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    Thanks zenerdiode. Not sure I can leave the car with the bonnet unlocked in my neighbourhood, but I appreciate your suggestion.
    With regards to the seatbelt- I feel sure I have moved the car around on my drive with no seatbelt on, so perhaps the buckle switch is not an issue.
    I'm pulling what's left of my hair out trying to solve this as my wife has previously refused to get in the car with me as the failing to release the autohold or handbrake has caused me some issues at junctions and whilst parking.
    Uwe- any clues among the battery readout?

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