2001 A6 4.2L goes into limp mode

   #1  

Gogo

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After multiple hours and checks with no obvious issues i determined the car was going into limp mode simply because the weather was cold. Minus 15 - minus 20 C. The battery was charged and analyzed and was found to be at 90%. It appears there is a voltage drop that initiates limp mode. As a solution a oil pan heater was installed, a battery warming blanket, and a battery maintenance charger. So far this has seemed to solve the problem of the car going into limp mode upon start up in cold weather although it has only been minus 4 C the last few days. The installed components are at best a crutch and it still needs to be determined what causes the voltage drop resulting in limp mode. If anyone has suggestions or possible solutions I am all ears.
 
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SaVAGeSoot

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What voltage drop? :confused:
 
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Gogo

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Voltage drop on initiate to start. Draw from starter and accessories.
 
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SaVAGeSoot

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To what? I didn't see any logs or anything showing this.
 
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Dr Sheldon

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If anyone has suggestions or possible solutions I am all ears.

Yes scope Voltage and Starter Motor Current Draw With nothing other than a Digital Storage Oscilloscope.
 
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Gogo

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How about a multimeter showing voltage as the engine cranks over. If you have a solution fine. If not it appears you are just trying to create friction.
 
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stefdds

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Since you are a relatively new member, you may not be aware that a complete and unedited Auto-Scan is asked for preceding any technical advice/help.

Also, I suspect the term "limp mode" you are using may be misplaced ; limp mode usually refers to a function with little or no power and limited functionality while operating down the road.
The Auto-Scan may reveal some voltage numbers that May add clarity.

 
   #9  

Gogo

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Code:
Saturday,04,January,2025,10:52:35:18730
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 11 x64
VCDS Version: 24.7.1.0 (x64)  HEX-V2 CB: 0.4643.4
Data version: 20240919 DS356.3
www.Ross-Tech.com


VIN: WAUZL54B71N155721   License Plate:
Mileage: 217640km-135235mi   Repair Order:



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


Chassis Type: 4B (4B - Audi A6/S6/RS6/allroad C5 (1998 > 2005))
Scan: 01 02 03 06 08 15 16 17 18 22 34 35 36 37 45 55 56 57 65 67
          75 76 77
 
VIN: WAUZL54B71N155721   Mileage: 217640km-135235miles
-------------------------------------------------------------------------------
Address 01: Engine        Labels: None
   Part No: 4D0 907 560 AE
   Component: 4.2l V8/5V      G   0003 
   Coding: 07752
   Shop #: WSC 02324 
   VCID: 698FABB1706D70E2E85-5118
   VINID: 9D196A7051121C17811451C204AE2EF0A9
   WAUZL54B71N155721     AUZ7Z0A1835027

No fault code found.
Readiness: 0110 1101

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 8D0-907-389.lbl
   Part No: 8D0 907 389 E
   Component: ABS/ESP allrad      D56 
   Coding: 06397
   Shop #: WSC 12345 
   VCID: 353737C16C55E402BCD-5160

No fault code found.

-------------------------------------------------------------------------------
Address 06: Seat Mem. Pass        Labels: None
   Part No: 4B0 959 760 C
   Component: Sitzmemory R1 BF    0102 
   Coding: 00003
   Shop #: WSC 00000 
   VCID: 2D071FA18405ACC2C4D-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 4B0-820-043-MY1.lbl
   Part No: 4B0 820 043 AH
   Component: A6-Klimavollautomat D65 
   Coding: 00080
   Shop #: WSC 02324 
   VCID: 6099B695835731AA3FB-25B6

No fault code found.

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 4B0-959-655-AI8.lbl
   Part No: 4B0 959 655 F
   Component: Airbag Front+Kopf  2002 
   Coding: 00405
   Shop #: WSC 02324 
   VCID: 333309D96221FA32929-5118

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel        Labels: 4B0-907-487.lbl
   Part No: 4B0 907 487 D
   Component: Lenkradelektronik    D03 
   Coding: 00102
   Shop #: WSC 65535 
   VCID: 2D071FA18405ACC2C4D-4FB8

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 4B0-920-xxx-17.lbl
   Part No: 4B0 920 933 B
   Component: C5-KOMBIINSTR. VDO D12  
   Coding: 03383
   Shop #: WSC 00001 
   VCID: 221DFC9DCDDB63BA69F-513C
   WAUZL54B71N155721     AUZ7Z0A1835027

No fault code found.

-------------------------------------------------------------------------------
Address 35: Centr. Locks        Labels:. 4B0-962-258.clb
   Part No: 4B0 962 258 J
   Component: Central Lock/Alarm  D34 
   Coding: 15885
   Shop #: WSC 02324 
   VCID: 303906D59337C12AEFB-4EEA

No fault code found.

-------------------------------------------------------------------------------
Address 36: Seat Mem. Drvr        Labels: None
   Part No: 4B0 959 760 B
   Component: Sitzmemory R1 F     0101 
   Coding: 00001
   Shop #: WSC 00000 
   VCID: 2C0112A5BF1FA5CAD33-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 45: Inter. Monitor        Labels: 4B0-951-178.lbl
   Part No: 4B0 951 178 A
   Component: Innenraumueberw.    D04 
   Coding: 00101
   Shop #: WSC 02324 
   VCID: 2615E08DA1F39F9A057-50AE

No fault code found.

-------------------------------------------------------------------------------
Address 55: Headlight Range        Labels: 4B0-907-357-DYN.lbl
   Part No: 4B0 907 357 C
   Component: dynamische LWR       D06 
   Coding: 00020
   Shop #: WSC 02324 
   VCID: 2809EEB5ABE789EA37B-4B5C

1 Fault Found:
00776 - Level Control System Sensor; Left Front (G78)
            31-00 - Open or Short to Ground

End----(Elapsed Time: 04:39, VBatt start/end: 11.7V/11.6V. VIgn 11.6V)-----
 
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   #10  

Gogo

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Since you are a relatively new member, you may not be aware that a complete and unedited Auto-Scan is asked for preceding any technical advice/help.

Also, I suspect the term "limp mode" you are using may be misplaced ; limp mode usually refers to a function with little or no power and limited functionality while operating down the road.
The Auto-Scan may reveal some voltage numbers that May add clarity.

Limp mode being the car when put in D defaults to 3rd or 4th gear resulting in slow acceleration. The indicator for the PRND234 are all red and the gear selected is not highlighted as is the normal case when the auto is not in limp.
 
   #11  

SaVAGeSoot

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That's TCU limp mode... See how your 02 controller is missing from the scan?
 
   #12  

Gogo

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That's TCU limp mode... See how your 02 controller is missing from the scan?
I can not access the TCU module. What the puzzling issue is that the car is just fine with zero issues at temperatures of plus 5 C and above. As the temperature drops to minus 3-5 C it takes a few restart tries to exit limp mode. As the temperature drops to minus 15 -20 it might exit limp mode after 10-15 restart cycles or it may not exit limp at all. The issue is definitely temperature related and as is the case in colder weather the crank time increases hence a voltage drop. As the TCU is solid state it should either work or fail and not be temperature sensitive. As posted previously a oil pan heater, battery blanket, and battery maintainer have improved starting and shortened crank times resulting in limp mode not activating with temperatures in the minus 5-10 C range. As the TCU is mounted under the passenger side carpet residual heat from the installed components has no effect. There is nothing wrong with the K line as I can access other modules. There is no K line short to ground.
 
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Dr Sheldon

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If anyone has suggestions or possible solutions I am all ears.

I dont think you are ? The Evidence is there !

Yes scope Voltage and Starter Motor Current Draw With nothing other than a Digital Storage Oscilloscope.

That there is your Silver Bullet.

How about a multimeter showing voltage as the engine cranks over. If you have a solution fine. If not it appears you are just trying to create friction.
Not the same as an Oscilloscope - Miles apart !!
 
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SaVAGeSoot

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I can not access the TCU module.
So if you can't "communicate" with it, do you think it can communicate with the rest of the network? (asking for a TCU friend) ;)
 
   #16  

dareckim11

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I think you have removed errors.

No fault code found. Readiness: 0110 1101

It is strange that the engine does not report errors.
Try to test drive a section of the road. Maybe it will show up.
If it appears, Paste auto-scan on the forum.
 
   #17  

NZDubNurd

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As the TCU is solid state it should either work or fail and not be temperature sensitive.
You can easily have "dry" solder joints, or components that have internal faults, or internal jumpers etc that can all be temperature related - as they contract or expand. there are also other, more complicated, ways components can cause issues from temeperatures, such as resistances near a limit, that alter with temp etc. It also tends to get much worse as they age.

VERY common in modules - probably second only to water damage, especially those exposed to temperature changes, such as in the engine bay, or nearby to exhausts etc.

Have you checked for water damage?

Your scan also shows a start voltage of 11.7V, which is pretty much flat. Some Auto transmissions are VERY voltage sensitive, though it wouldn't normally cause the TCU to go entirely offline.
 
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