Is using a battery tender absolutely required when working on the EPB?

jackofromtheuk · Jul 9, 2026

Hi, quick question.

I've always followed this to the letter:

https://wiki.ross-tech.com/wiki/index.php/Audi_A4_(8R/8K)_Parking_Brake_EPB-4

"Turn ignition off and leave battery charger connected."

How necessary is this? I need to remove the rear subframe for a few days (at best, a week or more depending on what I find) to replace the rear brake pipes. I'd rather not tie up my only charger or have to buy a new one.

I guess I could leave the EPB engaged while the subframe is dropped which would negate any risk but then it'll be detached from the car with no way to disengage (should I find a reason to, but I think the rear calipers could do with a rebuild and now is the prime time to do it).

Cheers. Attached is a scan from last year in case anyone needs the install list/coding, ignore any faults, think it was just after disconnecting the battery. Just a scan I happen to have to hand, it's currently got a clean bill of health except for the air quality sensor.

Code:

Sunday,13,July,2025,13:54:38:30949
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 24.5.0.0 (x64)
Data version: 20240429 DS355.0
www.Ross-Tech.com


VIN: WAUZZZ8K09A242007   License Plate:


Chassis Type: 8K-AU48 (8T0)
Scan: 01 03 05 08 09 15 16 17 19 42 46 47 52 53 56 62 72 77

VIN: WAUZZZ8K09A242007   Mileage: 275750km-171343miles

01-Engine -- Status: Malfunction 0010
03-ABS Brakes -- Status: OK 0000
04-Steering Angle -- Status: OK 0000
05-Acc/Start Auth. -- Status: OK 0000
08-Auto HVAC -- Status: Malfunction 0010
09-Cent. Elect. -- Status: Malfunction 0010
15-Airbags -- Status: OK 0000
16-Steering wheel -- Status: OK 0000
17-Instruments -- Status: OK 0000
19-CAN Gateway -- Status: Malfunction 0010
42-Door Elect, Driver -- Status: OK 0000
46-Central Conv. -- Status: OK 0000
47-Sound System -- Status: OK 0000
52-Door Elect, Pass. -- Status: OK 0000
53-Parking Brake -- Status: Malfunction 0010
56-Radio -- Status: Malfunction 0010
62-Door, Rear Left -- Status: OK 0000
72-Door, Rear Right -- Status: OK 0000
77-Telephone -- Status: OK 0000
 
-------------------------------------------------------------------------------
Address 01: Engine (J623-CAGA)       Labels:| 03L-906-022-CAG.clb
   Part No SW: 03L 906 022 MJ    HW: 03L 906 022 B
   Component: R4 2.0l TDI   H01 9978
   Revision: 11H01---    CVN: B5EFDC53
   Coding: 0104002C18072118
   Shop #: WSC 01930 002 1048576
   ASAM Dataset: EV_ECM20TDI03L906022MJ A01011
   ROD: EV_ECM20TDI03L906022.rod
   VCID: 79F866FCF8A1B75E04-802C
   VINID: 9D196AAAA21B0094421020001C3E2CD0FF

4 Faults Found:
5213 - Fuel Rail/System Pressure
          P0088 00 [01100000] - Too High
          Intermittent - Not Confirmed - Tested Since Memory Clear
5227 - Fuel Rail/System Pressure
          P0087 00 [01100000] - Too Low
          Intermittent - Not Confirmed - Tested Since Memory Clear
5231 - Fuel Rail/System Pressure
          P0087 00 [01100000] - Too Low
          Intermittent - Not Confirmed - Tested Since Memory Clear
5334 - Turbocharger Boost Control Position Sensor Circuit
          P2564 00 [00100000] - Signal too Low
          Intermittent - Not Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Priority: 2
                    Fault Frequency: 1
                    Mileage: 275577 km
                    Date: 2025.06.20
                    Time: 15:34:04

                    Engine RPM: 928.00 /min
                    Normed load value: 24.3 %
                    Vehicle speed: 0 km/h
                    Coolant temperature: 25 °C
                    Intake air temperature: 28 °C
                    Ambient air pressure: 1000 mbar
                    Voltage terminal 30: 11.300 V
                    Unlearning counter according OBD: 29
                    Crankshaft speed (RPM): 928.0 /min
                    Vehicle speed: 0.00 km/h
                    Vehicle voltage terminal 30: 11300 mV
                    Charge Pressure Actuator: activation: 100.00 %
                    Trb Ch r Drft Clsd mp: 9.41 %
                    Charge pressure adjuster position sensor: 1.0 mV

Readiness: 0 0 0 0 0

-------------------------------------------------------------------------------
Address 03: ABS Brakes (J104)       Labels:. 8K0-907-379-V1.clb
   Part No SW: 8K0 907 379 AE    HW: 8K0 907 379 AE
   Component: ESP8 front    H04 0240
   Revision: --------    Serial number: --------------
   Coding: 160500
   Shop #: WSC 06325 000 00000
   VCID: 7CF67FE8FF9382761F-8028

No fault code found.

-------------------------------------------------------------------------------
Address 05: Acc/Start Auth. (J393)       Labels:. 8K0-907-064-05.clb
   Part No SW: 8K0 907 064 C    HW: 8K0 907 064 C
   Component: BCM2 1.1      H80 0145
   Revision: 00002001  
   Coding: 031100
   Shop #: WSC 06325 000 00000
   VCID: 306E9BD8635BB616F3-8064

   Subsystem 1 - Part No SW: 8T0 959 754 D    HW: 8T0 959 754 D
   Component: FBSAUDIB8 IDG  H37 0060
   Serial number: 0509000023173018  

   Subsystem 2 - Part No SW: 8K0 905 852 D    HW: 8K0 905 852 D
   Component: J764 ELV MLB  H36 0042
   Serial number: 0209000027859011  

No fault code found.

-------------------------------------------------------------------------------
Address 08: Auto HVAC (J255)       Labels:. 8Tx-820-043-3Z.clb
   Part No SW: 8T2 820 043 S    HW: 8T2 820 043 S
   Component: KLIMA 3 ZONEN H06 0150
   Revision: D0000000    Serial number: 01140520090754
   Coding: 34040000
   Shop #: WSC 06325 000 00000
   VCID: 428AC110DDF7348615-8016

1 Fault Found:
00457 - Central Electronics Control Module / BCM (J519)
            013 - Check DTC Memory
             Freeze Frame:
                    Fault Status: 01101101
                    Fault Priority: 6
                    Fault Frequency: 254
                    Reset counter: 141
                    Mileage: 267862 km
                    Time Indication: 0
                    Date: 2024.01.26
                    Time: 14:50:46


-------------------------------------------------------------------------------
Address 09: Cent. Elect. (J519)       Labels:. 8K0-907-063.clb
   Part No SW: 8K0 907 063     HW: 8K0 907 063
   Component: BCM1 1.0      H26 0253
   Revision: 01026001    Serial number: 00000000266562
   Coding: 690040B10134BF000001000000005F5F001D020800000141000000
   Shop #: WSC 06325 123 12345
   VCID: 6CD64FA88FF312F68F-8038

   Subsystem 1 - Part No SW: 8K2 955 119 A    HW: 8T2 955 119   Labels: 1KX-955-119.CLB
   Component: WWS 080509  H05 0070
   Serial number: SWF09050085441    
   Coding: 00FD11

   Subsystem 2 - Part No SW: 8K0 955 559     HW: 8K0 955 559   Labels: 8K0-955-559.CLB
   Component: RLS  H04 0003
   Serial number: 10464619          
   Coding: 025028

   Subsystem 3 - Part No SW: 8K0 941 531 AA    HW: 8K0 941 531 AA
   Component: E1 - LDS  H07 0090
   Serial number: 00000000000605091945

1 Fault Found:
01592 - Air Quality Sensor (G238)
            014 - Defective
             Freeze Frame:
                    Fault Status: 01101110
                    Fault Priority: 3
                    Fault Frequency: 254
                    Reset counter: 141
                    Mileage: 267862 km
                    Time Indication: 0
                    Date: 2024.01.26
                    Time: 14:50:00


-------------------------------------------------------------------------------
Address 15: Airbags (J234)       Labels:| 8K0-959-655.clb
   Part No SW: 8K0 959 655 G    HW: 8K0 959 655 G
   Component: AirbagVW-AU10 H37 0520
   Serial number: 003EFD02J0H/   Dataset Number: 8K0909602F  0004
   Coding: 30363435363030303030554A3052384B3053
   Shop #: WSC 06325 000 00000
   ASAM Dataset: EV_AirbaECUVWAUDI010 003010
   ROD: EV_AirbaECUVWAUDI010_003_AU48.rod
   VCID: 4188CE1CD0F12F9E0C-8014

   Crash sensor for side airbag: driver side:
   Serial number: 6334MSME474423355

   Front Passenger's Side Airbag Crash Sensor:
   Serial number: 6344MSME4734347EK

   Rear Side Airbag Crash Sensor (on driver's side):
   Serial number: 6352QSME7F29193E.

   Passenger side rear thorax airbag crash sensor:
   Serial number: 6362QSME0A293F30K

   Crash sensor for front airbag: driver side:
   Serial number: 63732SME6626101CX

   Crash sensor for front airbag: front passenger side:
   Serial number: 63832SME5D2648364

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel (J527)       Labels:. 8K0-953-568.clb
   Part No SW: 8K0 953 568 F    HW: 8K0 953 568 F
   Component: Lenks.Modul   H16 0014
   Revision: --------    Serial number: 90319IE50005O
   Coding: 000016
   Shop #: WSC 06325 000 00000
   VCID: 3D70B2ECA4094B7E68-8068

   Component: E221 - MFL  H02 0003

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments (J285)       Labels:. 8T0-920-xxx-17.clb
   Part No SW: 8K0 920 980 B    HW: 8K0 920 980 B
   Component: KOMBIINSTR.   H18 0224
   Revision: 00200000    Serial number: 9E3105A59    
   Coding: 2F1D080002002600010001
   Shop #: WSC 06325 123 12345
   VCID: 31689EDC6851BF1EFC-8064

No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway (J533)       Labels:. 8T0-907-468.clb
   Part No SW: 8T0 907 468 M    HW: 8T0 907 468 H
   Component: GW-BEM 5CAN   H06 0095
   Revision: GB300043    Serial number: 4300G09509805C
   Coding: 000303
   Shop #: WSC 06325 000 00000
   VCID: 4B94EC34EABDF5CEE6-801E

   Subsystem 1 - Part No SW: 8K0 915 181 E    HW: 8K0 915 181 E
   Component: J367-BDM  H06 0160
   Serial number: 190773A0150409    

2 Faults Found:
02256 - Quiescent Current
            001 - Upper Limit Exceeded - Intermittent
             Freeze Frame:
                    Fault Status: 00100001
                    Fault Priority: 7
                    Fault Frequency: 7
                    Reset counter: 154
                    Mileage: 273399 km
                    Time Indication: 0
                    Date: 2024.12.25
                    Time: 17:30:00

03041 - Energy Management Active
            000 - - - Intermittent
             Freeze Frame:
                    Fault Status: 00100000
                    Fault Priority: 7
                    Fault Frequency: 17
                    Reset counter: 173
                    Mileage: 273437 km
                    Time Indication: 0
                    Date: 2024.12.29
                    Time: 15:03:00


-------------------------------------------------------------------------------
Address 42: Door Elect, Driver (J386)       Labels:. 8K0-959-793.clb
   Part No SW: 8K0 959 793 E    HW: 8K0 959 793 E
   Component: TSG FA        H11 0250
   Revision:             Serial number: 0000008807776
   Coding: 011002204001410001
   Shop #: WSC 06325 000 00000
   VCID: 428AC110DDF7348615-8016

No fault code found.

-------------------------------------------------------------------------------
Address 46: Central Conv. (J393)       Labels:. 8K0-907-064-46.clb
   Part No SW: 8K0 907 064 C    HW: 8K0 907 064 C
   Component: BCM2 1.1      H80 0145
   Revision: 00002001    Serial number: 0118097417  
   Coding: 011B062200390440012001
   Shop #: WSC 06325 123 12345
   VCID: 306E9BD8635BB616F3-8064

   Subsystem 1 - Part No: 8K0 951 177
   Component: DWA-Sensor  H02 0040

   Subsystem 2 - Part No: 1K0 951 605 C
   Component: LIN BACKUP HO  H03 1301

No fault code found.

-------------------------------------------------------------------------------
Address 47: Sound System (J525)       Labels:. 8T0-035-223-ASC.clb
   Part No SW: 8T0 035 223 AB    HW: 8T0 035 223
   Component: DSP STD       H07 0220
   Revision: S2100000  
   Coding: 0203010102
   Shop #: WSC 06325 000 00000
   VCID: 6ED245A0B9EFE0E6A1-803A

No fault code found.

-------------------------------------------------------------------------------
Address 52: Door Elect, Pass. (J387)       Labels:. 8K0-959-792.clb
   Part No SW: 8K0 959 792 E    HW: 8K0 959 792 E
   Component: TSG BF        H11 0250
   Revision:             Serial number: 0000008892402
   Coding: 011002204C01410001
   Shop #: WSC 06325 000 00000
   VCID: 4188CE1CD8F12F9E0C-8014

No fault code found.

-------------------------------------------------------------------------------
Address 53: Parking Brake (J540)       Labels: 8K0-907-801-V1.clb
   Part No SW: 8K0 907 801 G    HW: 8K0 907 801 G
   Component: EPB Audi B8   H08 0080
   Revision: 00000003    Serial number: 10000000224623
   Shop #: WSC 00000 000 00000
   VCID: 336494D4924D8D0E8E-8066

2 Faults Found:
02433 - Supply Voltage for Right Parking Brake Motor (V283)
            011 - Open Circuit - Intermittent
             Freeze Frame:
                    Fault Status: 00101011
                    Fault Priority: 1
                    Fault Frequency: 2
                    Reset counter: 86
                    Mileage: 274443 km
                    Time Indication: 0
                    Date: 2008.05.31
                    Time: 07:23:22

             Freeze Frame:
                    Voltage: 12.80 V
                    Count: 29
                    Speed: 0.0 km/h
                    Hex Value: 0x0173
                    Hex Value: 0x0008
                    Hex Value: 0x0101

02432 - Supply Voltage for Left Parking Brake Motor (V282)
            011 - Open Circuit - Intermittent
             Freeze Frame:
                    Fault Status: 00101011
                    Fault Priority: 1
                    Fault Frequency: 2
                    Reset counter: 86
                    Mileage: 274443 km
                    Time Indication: 0
                    Date: 2008.05.31
                    Time: 07:23:22

             Freeze Frame:
                    Voltage: 12.80 V
                    Count: 28
                    Speed: 0.0 km/h
                    Hex Value: 0x0163
                    Hex Value: 0x0008
                    Hex Value: 0x0101


-------------------------------------------------------------------------------
Address 56: Radio (J503)       Labels:. 8Tx-035-1xx-56.clb
   Part No SW: 8T2 035 195 AA    HW: 8T2 035 195 AA
   Component: Symphony3     H02 0310
   Revision: 00000005    Serial number: AUZ5Z4I1104501
   Coding: 0502008201018D008359070000
   Shop #: WSC 06325 000 00000
   VCID: 77FC60C4C6B5A12E72-8022

   Subsystem 1 - Part No SW: 8T0 919 603 E    HW: 8T0 919 603 E
   Component: Display

1 Fault Found:
03157 - Functionality limited due to Communications Disruption
            000 - -
             Freeze Frame:
                    Fault Status: 01100000
                    Fault Priority: 6
                    Fault Frequency: 254
                    Reset counter: 141
                    Mileage: 267862 km
                    Time Indication: 0
                    Date: 2024.01.26
                    Time: 14:50:00

             Freeze Frame:
                    Bin. Bits: 00000000
                    Bin. Bits: 00000001
                    Bin. Bits: 00000000
                    Bin. Bits: 00000000
                    Bin. Bits: 00000000
                    Bin. Bits: 00000000
                    Bin. Bits: 00000000
                    Bin. Bits: 00000000


-------------------------------------------------------------------------------
Address 62: Door, Rear Left (J388)       Labels:. 4F0-959-795.clb
   Part No SW: 4F0 959 795 N    HW: 8K0 959 795 C
   Component: TSG HL        H10 0251
   Revision:             Serial number: 0000101110886
   Coding: 010002204001210001
   Shop #: WSC 06325 000 00000
   VCID: 4486C708C7E33AB627-8010

No fault code found.

-------------------------------------------------------------------------------
Address 72: Door, Rear Right (J389)       Labels:. 4F0-959-795.clb
   Part No SW: 4F0 959 795 N    HW: 8K0 959 795 C
   Component: TSG HR        H10 0251
   Revision:             Serial number: 0000101110889
   Coding: 010002204001210001
   Shop #: WSC 06325 000 00000
   VCID: 4486C708C7E33AB627-8010

No fault code found.

-------------------------------------------------------------------------------
Address 77: Telephone        Labels: 8P0-862-335.lbl
   Part No SW: 8T0 862 335 C    HW: 8T0 862 335 C
   Component: FSE_256x BT     H33 0550
   Revision: 00000000    Serial number: 00000005075212
   Coding: 0010320
   Shop #: WSC 06325 000 00000
   VCID: 3A7AB9F075277C464D-806E

No fault code found.

End-------------------------(Elapsed Time: 03:05)--------------------------

Boki Ar · Jul 9, 2026

jackofromtheuk said:
"Turn ignition off and leave battery charger connected."

This message is present when we change e.g. rear pads.

If the car stays on the lift for several days, I would not leave the charger on. No need.

The suggestion would be for the EPB to be turned off, and you do everything that is necessary. If it is necessary to renew the rear brakes, use the charger while opening / closing / testing the rear calipers.

jackofromtheuk · Jul 9, 2026

Hmm yeah I could just leave it disengaged rather than retracted.

Thinking about it, it's not much more effort to do it in two stages since the only real convenience is having the brake system already dry, I can just leave it all disconnected once the subframe is back on then work on the calipers (if required).

Boki Ar · Jul 9, 2026

I agree. If the car is parked for several days, you can also disconnect the battery negative terminal. Maybe this would be best.

Uwe · Jul 9, 2026

jackofromtheuk said:
How necessary is this? I need to remove the rear subframe for a few days (at best, a week or more depending on what I find) to replace the rear brake pipes. I'd rather not tie up my only charger or have to buy a new one.

If the ignition is off while you're doing all this, you should be fine. What you don't want to do is to try to open or close the EPB while battery voltage is low.

What I would do in this case is: Make sure the battery is fully charged before you start, open the EPB (preferably with the charger still connected), then turn the ignition off and disconnect the charger.

Do the work you need to do for however long it takes. Once things are re-assembled, connect the charger again and make sure the battery is fully charged before turning the ignition on and closing the EPB (again, preferably with the charger connected).

-Uwe-

stefdds · Jul 9, 2026

Your title states "Battery tender" ; note, the forum recommends a battery Charger (10,20,30 amps). But, if you indeed are using a low amp Tender (under 5 amps) , you'll just have to wait alot longer if you are trying to bring voltage back up to a desired state.

Ziddywerks · Jul 9, 2026

Uwe said:
What you don't want to do is to try to open or close the EPB while battery voltage is low.

-Uwe-

I hear what you're saying and you are right, but even if you get jammed up in such a scenario there is a way to fix it but it comes down to having experience with these cars.

jackofromtheuk · Jul 9, 2026

Uwe said:
If the ignition is off while you're doing all this, you should be fine. What you don't want to do is to try to open or close the EPB while battery voltage is low.

What I would do in this case is: Make sure the battery is fully charged before you start, open the EPB (preferably with the charger still connected), then turn the ignition off and disconnect the charger.

Do the work you need to do for however long it takes. Once things are re-assembled, connect the charger again and make sure the battery is fully charged before turning the ignition on and closing the EPB (again, preferably with the charger connected).

-Uwe-

Ah makes sense, thanks. I'd read the ABS/EPB module is sensitive to low voltage, didn't know it was actually the action of opening/closing them.

stefdds said:
Your title states "Battery tender" ; note, the forum recommends a battery Charger (10,20,30 amps). But, if you indeed are using a low amp Tender (under 5 amps) , you'll just have to wait alot longer if you are trying to bring voltage back up to a desired state.

Yeah the difference is blurred these days as most chargers switch from charging to tending once the charge is sufficient. At least the ones I've used.

Uwe · Jul 9, 2026

jackofromtheuk said:
Yeah the difference is blurred these days as most chargers switch from charging to tending once the charge is sufficient. At least the ones I've used.

A charger may be able to act as a tender on a fully charged battery, but a tender is at best a very, very lame charger; i.e. it will not be able to maintain voltage of a battery in a car that has the ignition ON.

-Uwe-

Is using a battery tender absolutely required when working on the EPB?

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