This is going to be a slightly longer post as I present the scenario I am experiencing. Sorry for the inevitable wall of text.

Recently, I drove my A8 from my house to where it is currently residing during a mild rainstorm. The vehicle operated well within expectations from home to the location it is currently residing. I turned the vehicle off and took care of my business. This took roughly half an hour. When I went to restart the vehicle, it was sluggish to start, the idle was rough, and the gas peddle fluctuated between sluggish to non-responsive; with the vehicle ultimately stalling out. This pattern of behavior lead me to believe that the issue was likely electrical. The next day, I returned to the site with my VAGcom and got a reading consisting of 15 various "Short to Ground" errors across multiple systems. (VAG readout will be included at the end) The readout made me feel confident that I was on the proverbial right track. I researched where the main relay housing was located and how to dry the connections. My research lead me to the relay housing in the main engine compartment on the passenger side (US). I was disheartened to discover that the interior of the housing was bone dry, with no sign of moisture in it.

However, while doing this task, I discovered that the high pressure fuel pump on the left side of the engine (as observed from the front of the engine compartment) was leaking out the front of the pump and over the electrical relay that houses the Fule Pressure Regulator Valve. I have since ordered a replacement assemblage and have spent the rest of the night doing a deeper dive on the location of each individual fault presented in the VAG readout. The readout itself doesnt present anything about a fuel pump failure directly. Of the 15 faults it has thrown me, two are related to the Fuel Pressure Regulator Valve. These are the only two codes that I can find related directly to the assembly. Several of the other codes feel like they are part of the system but I have not been able to tie them into the system directly, as I do not currently have access an OEM repair manual (one is on the way). About half of the sensors throwing codes I have not been able to track down.

I am hoping that someone with more experience with the platform can examine the VAG readout below and tell me if these codes are all part of a cascading failure centered around the Fuel Pump I am about to replace or if I am looking at multiple unrelated failures. I am also open to any advice as to my next steps and observations on things I may have missed. I appreciate any help that the community is able to provide.


15 Faults Found:
009217 - EVAP Leak Detection Pump Control Circuit
P2401 - 002 - Short to GND - MIL ON
Freeze Frame:
Fault Status: 11100010
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 160882 km
Time Indication: 0
Date: 2024.10.21
Time: 15:13:43

Freeze Frame:
RPM: 701 /min
Load: 33.3 %
Speed: 0.0 km/h
Temperature: 90.0°C
Temperature: 51.0°C
Absolute Pres.: 1000.0 mbar
Voltage: 13.970 V

005224 - EVAP Canister Solenoid Valve 2 (N115)
P1468 - 002 - Short to Ground - MIL ON

004764 - Fuel Pressure Regulator Valve; Bank 2 (N276)
P129C - 002 - Short to Ground - Intermittent - MIL ON

004199 - Intake Air Switch-Over Valve (N335)
P1067 - 002 - Short to Ground

005173 - Secondary Air Pump Relay (J299)
P1435 - 002 - Short to Ground - MIL ON

001112 - Evap System Purge Control Valve (N80)
P0458 - 002 - Short to Ground - MIL ON

005494 - Right Engine Mount Solenoid Valve (N145)
P1576 - 002 - Short to Ground

005490 - Left Engine Mount Solenoid Valve (N144)
P1572 - 002 - Short to GroundqaXC

000258 - Mass Air Flow Sensor (G70)
P0102 - 002 - Signal too Low - MIL ON

005715 - Please check DTC Memory of ABS Controller
P1653 - 008 -

000048 - Oxygen (Lambda) Sensor B1 S1: Heating Circuit
P0030 - 004 - Malfunction / Open Circuit - MIL ON

000080 - Oxygen (Lambda) Sensor B2 S1: Heating Circuit
P0050 - 004 - Malfunction / Open Circuit - MIL ON

008853 - Fuel Pressure Regulator Valve (N276)
P2295 - 002 - Short to Ground - Intermittent - MIL ON

000054 - Oxygen (Lambda) Sensor B1 S2: Heating Circuit
P0036 - 004 - Malfunction / Open Circuit - MIL ON

000086 - Oxygen (Lambda) Sensor B2 S2: Heating Circuit
P0056 - 004 - Malfunction / Open Circuit - MIL ON

Readiness: 0000 0000

 

Fix the obvious problem first (leaking HPFP), clear all the fault codes and see which one’s come back after running it.

 

I appreciate the advice. It is the approach I was planning, I was just hoping someone may recognize how these systems either interact or dont and would be able to provide a little more insight on what to expect going forward based on the information that is available. I am hoping that this will clear the codes, but after reading the list presented on the VAG reading posts of people who have had similar problems, my concern here is that I am looking at two unrelated problems. I guess we will find out for sure in the next few days. I will be sure to let everyone know how it all plays out.

 

The resultant poor running, misfires, and low revs causing a low system voltage could be the mechanism for all the other errors. Lots of fault codes get triggered falsely with low voltage so best to ignore until you’ve eliminated other more obvious problems.