Bypass Valve Failure or somthing more?

[KnewJack]

2016 S5. Car threw a CEL yesterday while driving normally. Then hesitated and started sputtering under power. EPC light came on and went into limp mode with the do not exceed 4000rpm warning. Tried to limp home, but it died at a stop light and would not restart. Acted like fuel and spark were disabled. The codes I got on VCDS were P0652 Sensor Ref Voltage B too low and P10A6 Intake air regulator flap malfunction signal too low. Cleared codes and tried to restart. No dice. Codes came right back. Had it towed to my friends shop and hooked it up to his shop scanner which showed a host of codes all related to the bypass valve except one which was P019000 Fuel Pressure Sensor A circuit. Cleared the codes and still wouldn't start. Came back the next day and it started right up and idled normally.

Soon as I tried to drive it and give throttle it started misfiring and codes came back. Limped it back to the shop and it idled rough since EPC came back on. Turned it off and it would not restart. Removed the intake pipe and sprayed to some Carb cleaner in to see if it would start. It didn't which would indicate no spark too. Will the computer disable the car from a faulty Bypass valve? I remove the bypass valve and inspected it. Movement was a bit notchy in spots. Plugged it in and it jerked closed then opened. put it back together and codes would not reset and car would not start. Do I need to get a new Bypass valve or could it be something else?

[djn876]

Can you list all of the codes that you got?

Internal gears on BPV have failed before, but that shouldnt have anything to do with fuel pressure being low. If you can find a used one and swap it for cheap, would be an easy thing to check first. Even if you have someone with a 3.0t nearby maybe you could just swap it on the car before even buying one.

[KnewJack]

Had time to look at it more this week. There were a host of codes before installing new Bypass.



Car would not start at all. I unplugged the bypass valve and it started up. So ordered new one.

After installing new bypass and clearing codes, previous codes were gone, but a new code popped up.



Car started and drove fine for about 10 minutes then EPC light came on and it started to misfire. Parked it for the night to mess with it next day.
Next day bring my VCDS and hooked it up. Old codes were present from the 1st image minus the fuel pressure code. Reset them and only 3 came back. Car would not start however. No fuel no spark and EPC light on.



These 3 codes continue to stay and will not clear. With bypass plugged in or unplugged, same codes, no start. Tried a hard reboot by disconnecting neg and pos terminals and touching them together for about an hour. (suggested by Volks/Audi dealer tech to clear mysterious computer issues). Hooked terminals back up, no EPC light and no CEL. Still no start. after sitting with key on, EPC did return and CEL with same codes from last image. Checked all fuses in engine compartment box and also tried jumping the ECM power supply relay to see if that was the problem. not sure what to do from here. Hand it over to a pro I guess unless someone here has some suggestions.

[KnewJack]

For the archives, it turned out to be a faulty boost pressure sensor.

[Method]

Thanks for coming back with the solution - much appreciated!

[KnewJack]

No Problem, the board was pretty silent on this issue Lol. Figured I'd post the resolution anyway. When I couldn't figure out what was going on I just took a multi meter and started checking voltages and continuity with the key on. Thought maybe a rat got in and chewed something. First I tested the bypass sensor plug which gave 5 volts on the power pin but when I got to the drivers side Boost Sensor I only got 2.5v and a dim light. Looking at the plug closer there was some corrosion in the power pin as well as on the sensor itself. Apparently some moisture had gotten in there. My thought is that it was sending feedback to the ECM and also fowled the sensor itself. I cleaned the connector really well and the old sensor, but was still having the same issue. However if I unplugged the boost sensor the car would start up and run fine. Soon as I plugged in the sensor in the car would die. Replaced boost sensor and all was well. Codes cleared no problem.