Stranded - A8 Does Not Start Due To Electrical Problems
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Stranded - A8 Does Not Start Due To Electrical Problems
In the last two days my 2007 A8L 4.2 D3 fails to start, many VCDS DCT point towards electrical issues, but:
1. battery is charged
2. dash, MMI come on
3. all electrical functions are working
4. starter is working, but engine won't start
I suspect that one of the fuel pumps is not working correctly or the board managing it.
car has 98,887 miles and is driven rarely, often just once a week
--- brief history of past issues, for context ---
> 2020.06.02
> MMI screen gears are broken, screen going up/down stops half way w/ a very loud noise
> after research for solutions here on Audi World, decided to cut blue/white wire under passenger side panel / floor to stop/prevent the MMI screen mechanism from going up/down
> there were (2) blue/white wires, unclear which one to cut, I only cut one (1) of these wires - wrapped tape around each wire end
> screen up/down mechanism is not engaged anymore, so this was "successful" in that regard
> given the next points, I feel this is the event that started it all - but may just be coincidence
> 2020.06
> battery now starts acting up, it gets harder to start the car
> the is still the original Audi battery, which had no issues so far
> 2020.12.10
> over the last months, the car has had more and more issues starting
> today it fails to start, starter tries but engine won't turn
> trickle charged the battery for 90 mins @ 10 amps, car then starts
> this indicated a battery issue to me
> replaced OEM battery w/ Duralast Platinum Battery H9-AGM Group Size H9/LN6 950 CCA
> re-coded battery in VCDS
> all symptoms gone
> 2023.10.08
> car is again failing to start
> same symptoms as above
> VCDS w/ car failing to start
012425 - Signal Line for Fuel Pump Electronics
P3089 - 002 - Electrical Malfunction
> trickle charging the battery helps to get the car started
> VCDS after trickle charging the battery
012425 - Signal Line for Fuel Pump Electronics
P3089 - 002 - Electrical Malfunction - Intermittent
> this premium battery is less than (3) years old, w/ the car barely being used
> replaced the battery again w/ same premium make/model
> re-coded battery in VCDS
> car now start again just fine, symptoms gone
> 2024.09
> drove to store, 15-20 mins drive
> after 30 mins return to car and drove out backwards from parking spot w/ AC turned on
> iow: rear camera was activated and AC was running, both use electricity while the car just started up
> 40 secs later the car dies while idle
> I start the car again while pumping gas pedal, it runs but stutters and rpm drop until the car dies
> waited for 10+ mins, then start the car again and manage to get it to rev up by pumping gas pedal - somehow the 10+ mins wait time helped, something seemed to have reset in that time frame
> my initial (non-expert) thought was that somehow, by driving out backwards while using AC (uses more electricity), it maybe drained the battery
> 2025.0712
> car has been running fine in last 10 months, no issues
> during a longer drive (w/ a few stops) the AC starts turning itself on every 30 secs. I turn it off, and 30 secs later it turns itself back on.
> 2025.07.20
> AC issue from last week is gone
> today same issue as 2024.09: I drive out backward from parking spot while bringing both front windows down, iow: using electricity for rear camera and windows, car dies 30 secs later - same as above
> restart attempts always die
> waited for 10+ mins, then managed to get the car running, same as above
> 2025.07.26
> car was not driven in last 6 days since incident above, and now fails to start again
> this premium battery is less than (2) years old - but maybe the last event drained the battery
> VCDS OBD II (did not do full scan)
VCDS Release 23.3.1 (x64): Generic OBD2
Mode 03: Emission related fault codes
Address 7E8: 1 Fault Found:
P025C - Fuel Pump Control Module: Short to Ground
Address 7E9: No fault code found.
> trickle charged the car for 90+ mins
> pressing START button to start the car now does nothing it aborts the start attempt after 1 secs - never seen that before
> using car key physically to start the car works and manage to start the car
> so again charging the battery allows to start the car - this indicates again battery issues
> drove the car for 10+ mins
> did a full VCDS readout afterwards
> it lists a few electrical issues: HVAC, side mirrors, seat heating, etc
> and again fuel pump now states intermittent again
012425 - Signal Line for Fuel Pump Electronics
P3089 - 002 - Electrical Malfunction - Intermittent
given the history so far, the fix was always to simply replace the battery as potentially something was draining/killing if over time.
new battery managed to start the car, all other electrical functions worked.
> 2025.07.27
> plan is to to start the car and go get a new battery, replace the current one and see if that fixes the problem again.
> car will not start, not even after 90+ min trickle charging, which always helped so far, incl.yday
> AAA comes and attaches larger power brick to battery to help start the car - it does not
> seems like fuel pump is not working correctly (for whatever reason)
> afterwards, I trickle charge the battery for another 4 hrs - then try again - car will not start
here's a full VCDS log from today after last attempt
it does list some items as Malfunction but funny enough the electrical items do work
Questions:
(1) any idea why changing the battery always fixed the problem in the past?
(2) how to proceed from here, what can I do to identify the issue for the car not starting?
I would really like to identify the issue myself first before potentially towing the car to a mechanic as I had very bad experiences in the past - lots of money and time wasted.
(3) how to test or fix the signal line to the fuel pumps (listed as fault), maybe this is the electrical issue that ultimately won't start the car?
Any guidance, help or info much appreciated.
Thanks!
1. battery is charged
2. dash, MMI come on
3. all electrical functions are working
4. starter is working, but engine won't start
I suspect that one of the fuel pumps is not working correctly or the board managing it.
car has 98,887 miles and is driven rarely, often just once a week
--- brief history of past issues, for context ---
> 2020.06.02
> MMI screen gears are broken, screen going up/down stops half way w/ a very loud noise
> after research for solutions here on Audi World, decided to cut blue/white wire under passenger side panel / floor to stop/prevent the MMI screen mechanism from going up/down
> there were (2) blue/white wires, unclear which one to cut, I only cut one (1) of these wires - wrapped tape around each wire end
> screen up/down mechanism is not engaged anymore, so this was "successful" in that regard
> given the next points, I feel this is the event that started it all - but may just be coincidence
> 2020.06
> battery now starts acting up, it gets harder to start the car
> the is still the original Audi battery, which had no issues so far
> 2020.12.10
> over the last months, the car has had more and more issues starting
> today it fails to start, starter tries but engine won't turn
> trickle charged the battery for 90 mins @ 10 amps, car then starts
> this indicated a battery issue to me
> replaced OEM battery w/ Duralast Platinum Battery H9-AGM Group Size H9/LN6 950 CCA
> re-coded battery in VCDS
> all symptoms gone
> 2023.10.08
> car is again failing to start
> same symptoms as above
> VCDS w/ car failing to start
012425 - Signal Line for Fuel Pump Electronics
P3089 - 002 - Electrical Malfunction
> trickle charging the battery helps to get the car started
> VCDS after trickle charging the battery
012425 - Signal Line for Fuel Pump Electronics
P3089 - 002 - Electrical Malfunction - Intermittent
> this premium battery is less than (3) years old, w/ the car barely being used
> replaced the battery again w/ same premium make/model
> re-coded battery in VCDS
> car now start again just fine, symptoms gone
> 2024.09
> drove to store, 15-20 mins drive
> after 30 mins return to car and drove out backwards from parking spot w/ AC turned on
> iow: rear camera was activated and AC was running, both use electricity while the car just started up
> 40 secs later the car dies while idle
> I start the car again while pumping gas pedal, it runs but stutters and rpm drop until the car dies
> waited for 10+ mins, then start the car again and manage to get it to rev up by pumping gas pedal - somehow the 10+ mins wait time helped, something seemed to have reset in that time frame
> my initial (non-expert) thought was that somehow, by driving out backwards while using AC (uses more electricity), it maybe drained the battery
> 2025.0712
> car has been running fine in last 10 months, no issues
> during a longer drive (w/ a few stops) the AC starts turning itself on every 30 secs. I turn it off, and 30 secs later it turns itself back on.
> 2025.07.20
> AC issue from last week is gone
> today same issue as 2024.09: I drive out backward from parking spot while bringing both front windows down, iow: using electricity for rear camera and windows, car dies 30 secs later - same as above
> restart attempts always die
> waited for 10+ mins, then managed to get the car running, same as above
> 2025.07.26
> car was not driven in last 6 days since incident above, and now fails to start again
> this premium battery is less than (2) years old - but maybe the last event drained the battery
> VCDS OBD II (did not do full scan)
VCDS Release 23.3.1 (x64): Generic OBD2
Mode 03: Emission related fault codes
Address 7E8: 1 Fault Found:
P025C - Fuel Pump Control Module: Short to Ground
Address 7E9: No fault code found.
> trickle charged the car for 90+ mins
> pressing START button to start the car now does nothing it aborts the start attempt after 1 secs - never seen that before
> using car key physically to start the car works and manage to start the car
> so again charging the battery allows to start the car - this indicates again battery issues
> drove the car for 10+ mins
> did a full VCDS readout afterwards
> it lists a few electrical issues: HVAC, side mirrors, seat heating, etc
> and again fuel pump now states intermittent again
012425 - Signal Line for Fuel Pump Electronics
P3089 - 002 - Electrical Malfunction - Intermittent
given the history so far, the fix was always to simply replace the battery as potentially something was draining/killing if over time.
new battery managed to start the car, all other electrical functions worked.
> 2025.07.27
> plan is to to start the car and go get a new battery, replace the current one and see if that fixes the problem again.
> car will not start, not even after 90+ min trickle charging, which always helped so far, incl.yday
> AAA comes and attaches larger power brick to battery to help start the car - it does not
> seems like fuel pump is not working correctly (for whatever reason)
> afterwards, I trickle charge the battery for another 4 hrs - then try again - car will not start
here's a full VCDS log from today after last attempt
it does list some items as Malfunction but funny enough the electrical items do work
Spoiler
Questions:
(1) any idea why changing the battery always fixed the problem in the past?
(2) how to proceed from here, what can I do to identify the issue for the car not starting?
I would really like to identify the issue myself first before potentially towing the car to a mechanic as I had very bad experiences in the past - lots of money and time wasted.
(3) how to test or fix the signal line to the fuel pumps (listed as fault), maybe this is the electrical issue that ultimately won't start the car?
Any guidance, help or info much appreciated.
Thanks!
Last edited by audi_la; Jul 27, 2025 at 11:50 PM.
Thread Starter
AudiWorld Junior Member
Joined: Dec 2020
Posts: 27
Likes: 0
update:
removed the battery and brought it to Autozone to had it tested.
they say battery is fine and at 100% and it should deliver the cranking power as per spec.
this is good news but actually really bad news :-(
was hoping it was the battery.
any suggestions how to go from here much appreciated.
removed the battery and brought it to Autozone to had it tested.
they say battery is fine and at 100% and it should deliver the cranking power as per spec.
this is good news but actually really bad news :-(
was hoping it was the battery.
any suggestions how to go from here much appreciated.
Last edited by audi_la; Jul 28, 2025 at 09:08 PM.
AudiWorld Member
Joined: Sep 2018
Posts: 394
Likes: 54
What you are describing where the car starts and runs for 30 sec and then dies sounds like the fuel pumps in the trunk are going out. The first one engages for 30 sec on startup and feeds the 2nd one after which takes over in normal operation. I would start with the fueling related codes/issues and go from there.
Thread Starter
AudiWorld Junior Member
Joined: Dec 2020
Posts: 27
Likes: 0
What you are describing where the car starts and runs for 30 sec and then dies sounds like the fuel pumps in the trunk are going out. The first one engages for 30 sec on startup and feeds the 2nd one after which takes over in normal operation. I would start with the fueling related codes/issues and go from there.
Trying to understand what the next steps are in systematic order to identify the root cause, if we are for now focusing on the fuel pumps.
does this make sense?
1 - check the fuel pump relays
2 - check the fuel delivery module
3 - check the primary fuel pump itself
Any tips, info would be extremely helpful in not only the order of things to check but then what tests to do to identify a broken part.
Yesterday I tried finding the fuel pump relays, which there should be (2), one for each fuel pump, but could not identify them.
during my research here on AW, I found this image but I still do not know where the location is in the car for either:
Last edited by audi_la; Jul 29, 2025 at 10:32 AM.
Thread Starter
AudiWorld Junior Member
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but, I must be missing something.
he says he checked all fuses.
he then says he did not check the fuel pump relays.
we then see the location of both fuel pumps.
he then says he has replaced both fuel pumps.
I don't see where he shows the location of the fuel pump relays.
is it here?
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Thread Starter
AudiWorld Junior Member
Joined: Dec 2020
Posts: 27
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same here, but I don't know if the relay diagram I posted above is correct for 2007 A8 D3, and if it is, I did not identify the relays when I looked.
and I could not see the fuel pump relays locations in the video.
I will look again for the relays now!
if you could comment on the general order of tests that I should do (re fuel pump), that would be greatly appreciated.
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Thread Starter
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ok, small progress here.
Identified the fuel pump relays - hope this helps somebody else.
the diagram I posted above seems to be correct for 2007 A8 D3, but the physical labels on the relays are not J17 or J49.
(1) passenger footwell has 5x relays
4th relay form the top w/ physical label 614 is relay J17 for the pre-supply pump G6
(2) trunk, right side, above battery, behind post has 3x relays
the relay directly behind the post labeled 614 again (#3 on the diagram above) is relay J49 for main fuel pump G23
would deeply appreciate it if someone can guide me on the correct order of steps to identify fuel pump related issues, i.e. what is the most efficient way of approaching this
for example, should I measure the voltage the fuel pumps are getting (I think the pump has a purple plug that supplies power) to identify a faulty fuel pump relay J17 | J49... ?
never done any of this before so the more detail, the better.
Thanks a bunch!
Identified the fuel pump relays - hope this helps somebody else.
the diagram I posted above seems to be correct for 2007 A8 D3, but the physical labels on the relays are not J17 or J49.
(1) passenger footwell has 5x relays
4th relay form the top w/ physical label 614 is relay J17 for the pre-supply pump G6
(2) trunk, right side, above battery, behind post has 3x relays
the relay directly behind the post labeled 614 again (#3 on the diagram above) is relay J49 for main fuel pump G23
would deeply appreciate it if someone can guide me on the correct order of steps to identify fuel pump related issues, i.e. what is the most efficient way of approaching this
for example, should I measure the voltage the fuel pumps are getting (I think the pump has a purple plug that supplies power) to identify a faulty fuel pump relay J17 | J49... ?
never done any of this before so the more detail, the better.
Thanks a bunch!
AudiWorld Member
Joined: Sep 2018
Posts: 394
Likes: 54
There is a procedure in the 26-Service Manual fuel supply system petrol engines service doc for testing the pumps and harness. Section 3.2 and 3.5. Search is your friend if you need the manuals. It involves running the pumps by applying voltage at the appropriate fuse point and listening for the pump motor activation. If you think it is a relay, you can find another 614 that is used for something else and swap them out to see if the situation improves or a new problem pops up. The in tank units are a known failure point with the symptoms you describe. Measurement on each unit using the method as described should read 8A.