How does cold bulb diagnostics work

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MVB_

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Trying to find anything I can read about cold/ hot bulb diagnostics. Thanks

Code:
Thursday,27,October,2016,13:39:19:05634
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 8.1 x86
VCDS Version: 16.8.3.1
Data version: 20161010 DS267.0
www.Ross-Tech.com


VIN: WVWEV71K18W28 License Plate: 10-27-16
Mileage: 73660km-45770mi   Repair Order: 



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: 1K (1K0)
Scan: 01 03 08 09 0F 15 16 17 19 25 37 42 44 46 47 52 55 56 65

VIN: WVWEV71K18W28   Mileage: 73660km-45770miles

01-Engine -- Status: OK 0000
03-ABS Brakes -- Status: OK 0000
04-Steering Angle -- Status: OK 0000
08-Auto HVAC -- Status: OK 0000
09-Cent. Elect. -- Status: OK 0000
0F-Digital Radio -- Status: Malfunction 0010
15-Airbags -- Status: OK 0000
16-Steering wheel -- Status: OK 0000
17-Instruments -- Status: OK 0000
19-CAN Gateway -- Status: OK 0000
25-Immobilizer -- Status: OK 0000
37-Navigation -- Status: OK 0000
42-Door Elect, Driver -- Status: OK 0000
44-Steering Assist -- Status: OK 0000
46-Central Conv. -- Status: OK 0000
47-Sound System -- Status: OK 0000
52-Door Elect, Pass. -- Status: OK 0000
55-Headlight Range -- Status: OK 0000
56-Radio -- Status: OK 0000
65-Tire Pressure -- Status: OK 0000
 
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 06F-907-115-AXX.clb
   Part No SW: 1K0 907 115 S    HW: 8P0 907 115 B
   Component: 2.0l R4/4V TFSI     0020  
   Revision: 5BH16---    Serial number: VWX7Z0H23N78HA
   Coding: 0403010A18070160
   Shop #: WSC 01279 785 00200
   VCID: 366901F741517FF256-8062

No fault code found.
Readiness: 0000 0000

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 1K0-907-379-MK60-F.lbl
   Part No SW: 1K0 907 379 AC    HW: 1K0 907 379 AC
   Component: ESP FRONT MK60      0101  
   Revision: 00H11001    
   Coding: 0021122
   Shop #: WSC 01279 785 00200
   VCID: 73EFF8E312A32ADAB1-8026

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 1K0-820-047.lbl
   Part No SW: 1K0 820 047 HS    HW: 1K0 820 047 HS
   Component: Climatic PQ35   142 1111  
   Revision: 00142031    Serial number: 00000000000000
   Shop #: WSC 00000 000 00000
   VCID: 7CFDD3DF3FFD65A2E0-8028

No fault code found.

-------------------------------------------------------------------------------
Address 09: Cent. Elect.        Labels: 3C0-937-049-30-H.lbl
   Part No SW: 3C0 937 049 AJ    HW: 3C0 937 049 AJ
   Component: Bordnetz-SG     H54 2202  
   Revision: 00H54000    Serial number: 00000008138279
   Coding: 178D8F214004150047140000001400000028770B5C000100000000000000
   Shop #: WSC 00000 785 00200
   VCID: 71E3F2EB68BF18CA43-8024

   Subsystem 1 - Part No: 1K1 955 119 E  Labels: 1KX-955-119.CLB
   Component: Wischer 050308 021  0501  
   Coding: 00038805
   Shop #: WSC 00000  

No fault code found.

-------------------------------------------------------------------------------
Address 0F: Digital Radio        Labels: 8E0-035-593-SIR.lbl
   Part No SW: 8E0 035 593 M    HW: 8E0 035 593 M
   Component: SDAR SIRIUS     H07 0150  
   Revision: 00000000    Serial number: AUZ4Z7H0275604
   Coding: 0000000
   Shop #: WSC 00000 000 00000
   VCID: 336F38E352236ADA71-8066

1 Fault Found:
02635 - Tuner Not Enabled/Activated 
            000 -  - 
             Freeze Frame:
                    Fault Status: 01100000
                    Fault Priority: 7
                    Fault Frequency: 2
                    Reset counter: 136
                    Mileage: 73635 km
                    Time Indication: 0
                    Date: 2000.00.00
                    Time: 12:51:52


-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 1K0-909-605.lbl
   Part No SW: 1K0 909 605 AB    HW: 1K0 909 605 AB
   Component: 6K AIRBAG VW8R  034 8000  
   Revision: 05034000    Serial number: 003B6D0AT5E5  
   Coding: 0013899
   Shop #: WSC 01269 785 00200
   VCID: 6CDDE39F4F9DF52270-8038

   Subsystem 1 - Part No: 1K0 959 339 G
   Component: BF-Gewichtsens. 007 0007

   Subsystem 2 - Serial number: 6332MSME394244311

   Subsystem 3 - Serial number: 6342MSME2E32735AI

   Subsystem 4 - Serial number: 6352QSME5B497921P

   Subsystem 5 - Serial number: 6362QSME581B3F0F-

   Subsystem 6 - Serial number: 63727SME14173134R

   Subsystem 7 - Serial number: 63827SME14331A41V

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel        Labels: 1K0-953-549-MY8.lbl
   Part No SW: 1K0 953 549 BP    HW: 1K0 953 549 BP
   Component: J0527           752 0100  
   Coding: 0002022
   Shop #: WSC 01279 785 00200
   VCID: 0103A22B581F084AB3-8054

   Subsystem 1 - Part No: XXXXXXXXXXX 
   Component: E0221           002 0010

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 1K0-920-xxx-17.lbl
   Part No SW: 1K6 920 974 A    HW: 1K6 920 974 A
   Component: KOMBIINSTRUMENT VDD 2216  
   Revision: V0002000    Serial number: VWX7Z0H23N78HA
   Coding: 0007203
   Shop #: WSC 00000 785 00200
   VCID: 32613DE7AD3963D27A-8066

No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway        Labels: 1K0-907-530-V3.clb
   Part No SW: 1K0 907 530 L    HW: 1K0 907 951 
   Component: J533  Gateway   H07 0052  
   Revision:   H07 01    Serial number: 060308F2001324
   Coding: E9811F075003020000
   Shop #: WSC 01279 785 00200
   VCID: 306537EFA33551C20C-8064

No fault code found.

-------------------------------------------------------------------------------
Address 25: Immobilizer        Labels: 1K0-920-xxx-25.clb
   Part No SW: 1K6 920 974 A    HW: 1K6 920 974 A
   Component: IMMO            VDD 2216  
   Revision: V0002000    Serial number: VWX7Z0H23N78HA
   Shop #: WSC 09128 444 84839
   VCID: 32613DE7AD3963D27A-8066

No fault code found.

-------------------------------------------------------------------------------
Address 37: Navigation        Labels: 1K0-919-887-MFD2.lbl
   Part No: 1K0 919 887 GX
   Component:      Navigation     0050  
   Coding: 0000101
   Shop #: WSC 12345 123 12345
   VCID: 152BE67B3C9794EA7F-8040

No fault code found.

-------------------------------------------------------------------------------
Address 42: Door Elect, Driver        Labels: 1K0-959-701-MIN3.lbl
   Part No SW: 1K0 959 701 M    HW: 1K0 959 701 M
   Component: Tuer-SG         006 1207  
   Coding: 0001077
   Shop #: WSC 01279 785 00200
   VCID: 38750FCF4B45898244-806C

No fault code found.

-------------------------------------------------------------------------------
Address 44: Steering Assist        Labels: 1Kx-909-14x-44.clb
   Part No: 1K1 909 144 M
   Component: EPS_ZFLS Kl.074 H08 1901  
   Shop #: WSC 00000 028 00001
   VCID: 356B06FB5C5774EA5F-8060

No fault code found.

-------------------------------------------------------------------------------
Address 46: Central Conv.        Labels: 1K0-959-433-MAX.clb
   Part No SW: 1K0 959 433 CT    HW: 1K0 959 433 CT
   Component:    KSG PQ35 RDK 052 0221  
   Revision: 00052000    Serial number: 00000000000000
   Coding: 13900E885103403F2D04058FB0080A04889C00
   Shop #: WSC 09128 444 84839
   VCID: 040DAB3F470D1D6298-8050

   Subsystem 1 - Component:   Sounder n.mounted     

   Subsystem 2 - Component:       NGS n.mounted     

   Subsystem 3 - Component:      IRUE n.mounted     

No fault code found.

-------------------------------------------------------------------------------
Address 47: Sound System        Labels: 3C0-035-456.lbl
   Part No SW: 1K6 035 456 B    HW: 1K6 035 456 B
   Component: 08K Audioverst.     0006  
   Revision: 00004000    Serial number: 00000008137952
   Shop #: WSC 00000 000 00000
   VCID: 2B5F20838A13321A39-807E

No fault code found.

-------------------------------------------------------------------------------
Address 52: Door Elect, Pass.        Labels: 1K0-959-702-MIN3.lbl
   Part No SW: 1K0 959 702 M    HW: 1K0 959 702 M
   Component: Tuer-SG         006 1207  
   Coding: 0001076
   Shop #: WSC 01279 785 00200
   VCID: 39730ACB704F908ABB-806C

No fault code found.

-------------------------------------------------------------------------------
Address 55: Headlight Range        Labels: 1T0-907-357.lbl
   Part No: 1T0 907 357 
   Component: Dynamische LWR      0003  
   Coding: 0000003
   Shop #: WSC 01279 785 00200
   VCID: 74EDFBFF17AD2DE2A8-8020

No fault code found.

-------------------------------------------------------------------------------
Address 56: Radio        Labels: 1K0-035-095.lbl
   Part No: 1K0 035 095 HX
   Component:        Radio        0050  
   Coding: 0010046
   Shop #: WSC 09130 444 84839
   VCID: 0201AD275D191352AA-8056

No fault code found.

-------------------------------------------------------------------------------
Address 65: Tire Pressure        Labels: 3C0-959-433-65.lbl
   Part No SW: 1K0 959 433 CT    HW: 1K0 959 433 CT
   Component:    RDK              0450  
   Revision: 00052000    Serial number: 00000000000000
   Coding: 0100101
   Shop #: WSC 01279 785 00200
   VCID: 040DAB3F470D1D6298-8050

No fault code found.

End-------------------------(Elapsed Time: 02:00)--------------------------
 
   #2  

Zenerdiode

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In general electonic engineering terms, lamp diagnostics is relatively easy. There's two main ways of doing it:

Cold Bulb Diagnostics
In cold bulb diagnostics, you pass a relatively small current through the filament (relatively, meaning relative to the 'normal' current that would flow to light the filament). By using a small current, the filament doesn't illuminate, hence 'cold bulb' Cold bulb has the advantage of the filament being continuously monitored. Very high value resistors are used so very small currents flow.

Hot Bulb Diagnostics
This measures the fact that current needs to flow to light the filament. The disadvantages are that the lamp diagnosis can only be carried out when the request to illuminate takes place. Very low value resistances are used in series with the filament and volt-drop over that resistance is used to prove current flow.
 
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MVB_

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So this is all monitored by the cent. elect. / vecm. Does the Cold Bulb Diagnostics just work at startup or is it active at all times until a bulb goes into use?
 
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DV52

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^^^^^^^ If I may add to Zenerdiode's excellent response. The value of the (small) constant-current injected into the various lighting circuits must be carefully selected so as not to be too low that it does not produce a detectable difference in voltage across the lamp when faulty, but not too high as to be inefficient, or to actually turn-on the lamp. For most "older" cars, the magnitude of the constant current source is selected specifically for incandescent lamps - which have a relatively high current requirement to illuminate the bulb - or a relatively low internal resistance.

Even though the design of the cold bulb diagnostic circuits is intended to produce a small current, there is voltage present to "drive" the electrical current through the filament resistance. A properly designed constant current circuit will increase its "driving" voltage until the specified current flow is achieved - in much the same way as a constant voltage circuit will increase its electrical current until the specified voltage is achieved. As an example, the deriving voltage of a constant current circuit which is designed for a few milliamps will rise to the full rail voltage of a car if the connected bulb resistance is sufficiently high

Problem is that when the lamps in these cars are replaced with LED fittings, the monitoring circuits see components with a very different electrical characteristics. LEDs are much more efficient producers of light (photons). They are also a constant current device by virtue of their design (as distinct from incandescent lamps which are ostensibly constant voltage devices) - LEDs enjoy being supplied by constant current circuits. But more importantly, LEDs have a relatively low "switch-on" voltage; the forward bias voltage of a LED is typically only a few volts - or lower. Which means that even though LEDs for car applications normally have a ballast resistor to regulate current, all that's needed to turn-on the LED is enough electrical current to produce this low forward bias voltage.

So, when cold bulb diagnostic circuits which expect to see incandescent bulbs are suddenly confronted by an LED - interesting things happen (especially if a "naked" LED with a simple resistor ballast is inserted). The cold bulb circuit starts to send-out it's designed (low) current level expecting to see the relatively low filament resistor of an incandescent lamp. However, what the circuit is confronted-with is the ballast resistor in the LED (which is typically in the order hundreds of ohms) plus the internal impedance of the LED . If the magnitude of the cold bulb current is insufficient to fire the LED, then the actual resistance that is seen is very high (because of the blocking impedance of the diode), but if the forward bias voltage is achieved, then the measured resistance will be hundreds of ohms.

"What the F#ck?" - the cold bulb circuit will say and errors will abound (plus the LED will invariably flash if the forward bias voltage is achieved)

Don
 
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Uwe

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Are you guys sure this is done using constant current sources? 'Cause that sounds more complicated than it needs to be.

If I were doing it for incandescent lamps with discreet components,
Hot: Just monitor the current being drawn when the bulb is lit. Assuming the switching transistor is a FET, you can do this by monitoring the voltage drop across the transistor itself.
Cold: Turn the bulb on a very short period of time, perhaps a millisecond. Not long enough to get the filament very warm, but plenty of time to check how much current is being drawn, and that current will be higher than when the bulb is hot because filaments tend to have a substantial temperature coefficient of resistivity.

Of course I expect none of this is done with anything resembling discreet components anymore, so to be sure, one would probably have to figure out which chip in the BCM is driving those lamps, and the get a data sheet for it...

-Uwe-
 
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DV52

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Are you guys sure this is done using constant current sources? 'Cause that sounds more complicated than it needs to be.

If I were doing it for incandescent lamps with discreet components,
Hot: Just monitor the current being drawn when the bulb is lit. Assuming the switching transistor is a FET, you can do this by monitoring the voltage drop across the transistor itself.
Cold: Turn the bulb on a very short period of time, perhaps a millisecond. Not long enough to get the filament very warm, but plenty of time to check how much current is being drawn, and that current will be higher than when the bulb is hot because filaments tend to have a substantial temperature coefficient of resistivity.

Of course I expect none of this is done with anything resembling discreet components anymore, so to be sure, one would probably have to figure out which chip in the BCM is driving those lamps, and the get a data sheet for it...

-Uwe-

Uwe: I'm sure that you are correct - and I probably over inflated the terminology in my response. And yes, I believe that the monitoring period for cold bulb monitoring is "pulsed". But it doesn't matter- the principles are exactly the same. inject a known current (my term- constant current) for a period of time into the thing that is plugged into the lamp socket and measure its resistance (when the "thing" is turned-off). I don't think that it matters whether the circuitry is a few discrete components (good to know that someone else remembers these!), or whether sophisticated VLSI circuitry is used that can actually accommodate both LEDs and incandescent bulbs.

Result: if an LED is connected, the "measured" resistance will be high (hundreds of ohms-or more). If an incandescent is plugged-in the resistance is low (for example a typical 21 watt incandescent operating at 12V should have a nominal "resistance" of around 6-7 ohms when fully illuminated, Since resistance in incandescent lamps increase as the lamp warms up, the cold-bulb monitoring circuit should expect to see a lower resistance than 6-7 ohms- I think!

Don
 
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MVB_

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Thanks for the posts, I have a better idea what is going on.
 
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