Loopback

Hi

Wondering if there is anyone that can help with a code P253900 - Low Pressure Fuel System Sensor Circuit issue on an 2011 Audi A6 C7 3.0TFSI..

A few months ago I did a 2 hour drive and once at the destination did a few short start stop trips. Car was performing well until I filled with fuel (wasn't low and had just less than 1/2 tank) and when I drove out of the petrol station the engine just cut out. There was no check engine light and when I tried to start it (didn't turn it off, just hit the start button) the car would start and idle but as soon as I tried to move the engine just stopped again. Engine wouldn't rev more than 1500 before stopping. I then decided to turn off the car, count to 30 and try again. When I did that the car ran great again and got home with no more problems. Plugged in my ODBeleven and got the following codes:-
Trouble codes:
P008700 - Fuel Rail/System Pressure - Too Low
Intermittent
P310B00 - Low Fuel Pressure regulation Fuel pressure outside specification
Intermittent
P253900 - Low Pressure Fuel System Sensor Circuit
Intermittent

Cleared the codes (they came back) and the car ran great again for a few months but recently the engine has started to stop again especially when its been run for a while and then followed by a few short trips - seems to be worse when the weather is hot (live in NZ so its getting nice). Leaving the car to cool down allows the engine to run fine again.

My research to date would indicate that the sensor on the side of the fuel pump (front left of engine) could be faulty (its listed as a HAL G40 sensor in the workshop manual but I've seen it referred to the Low Fuel Pressure Sensor as well). Before going and replacing it I just thought I'd ask you guys to get some advice on what it could be.

Many thanks and appreciate any help you guys have.

gk1

Sounds like your LPFP is dying.

Loopback

Thanks gk1 for the pointer, appreciate your quick response.
Was hoping for an easy (ish) fix by swapping out the sensor (G410 not G40 - bit of a typo) but doing more research this afternoon I think you might be right.
Because it looks like the sensor is fairly cheap (#06E906051K) I might swap that out first then go for the LPFP if that doesn't stop the codes from appearing.
Fingers crossed!

Loopback

Hi All

I've replaced the sensor and it appears to have fixed the issue. Its been running great again for a few days now and there are no codes being generated so I'm pretty sure its all fixed - the codes were generated every time I went for a ten minute drive before.

To replace the sensor I just removed the air intake and air box to get access to the sensor and then simply disconnected the sensor cable and then unscrewed the old one and put the new one in place, reconnect to the sensor cable and its done. If you are doing this too, there will be a small amount of fuel that will leak out when you remove the old sensor so make sure you've got a rag to soak it all up.

Thanks to gk1 for the help but it looks like I got lucky :0)

w.vdubs

was wondering if this was on the 3.0t and what made kniw it was fuel because on my s4 its cranking and not starting and its for sure a fuel issue.. everytime there is any presure in the rail it cuts power to the fuel pumps would it also be a sensor issue like you?

Loopback

Hi,
Yes it was the 3.0t and I read the codes from the car and that indicated an issue with the low pressure fuel sensor (see first post). I'm not a mechanic so can't tell you if its the sensor or not thats causing your issue but my engine would start and run up to about 1500 rpm then cut out.