Hi,

My 2007 A3 2.0t with 112,xxx miles and 6 speed manual transmission recently went into what I would assume is limp mode; hard starting, esp and check engine light are both on, very low power especially at higher revs. I drove to the auto parts store and had the codes read. The codes were P0087 (fuel rail/system pressure too low), P2293 (fuel pressure regulator 2 performance), and P2294 (fuel pressure regulator 2 control circuit).
I drove home and waited for the engine too cool and pulled the high pressure fuel pump expecting the follower to have failed, but to my relief, the follower was still in one piece although the black coating was worn off in the center so I replaced the follower as well as the fuel filter (was still on the original).
It was hard to start, but once it did it seemed to idle fine but the esp amd check engine lights were still on and the car still seemed to be in limp mode. I drove back to the auto parts store and had the codes cleared, it ran fine for about 1 mile then the performance dropped off and the lights came back on the next time I started the car. I scanned the codes again, and it is still the same ones.

So my problem is figuring out what is causing the code. I figure it could be a few things but I don't know how to narrow it down and I don't want to just start replacing parts without being sure.
Possibility 1: the high pressure fuel sensor has failed/is dirty.
Possibility 2: the low pressure fuel sensor has failed/is dirty.
Possibility 3: the fuel pressure regulator has failed.
Possibility 4: the high pressure fuel pump is not working properly anymore (I don't think this is the case since it looked in good shape when I pulled it but I don't know how to test)
Possibility 5: the low pressure fuel pump is not working properly.

I was planning on cleaning all the electrical connectors on these parts this evening and then disconnecting them one at a time to see if any of them affect performance when running.
My understanding (please correct me if I am wrong) is that the high pressure sensor is on the fuel rail, the low pressure sensor is on the left side (when facing the engine) of the high pressure pump, and the regulator is on the top of the high pressure pump.

Does anyone have any ideas or insights on how to narrow this down?

 

This will be a tough one to figure out. For know I'd leave the LPFP alone - as the errors you are pulling up are directly pointing at the HPFP.

HPFP is not something cheap to replace and there is no guarantee it is even the problem. The sensor throwing the code though is the little one on-top of the HPFP which I'm pretty sure cannot be replaced without the pump itself.
A worn camshaft is also plausible - however you said that cam follower and a visual inspection looked good.

My 2 cents would be to replace the Fuel pressure sensor first (on the fuel rail): 06J906051D as this would be the cheapest and a lot of other drivers has this part fail without a code pointing at it. Next on my list would be the HFPF.
Good luck and report back with results

(and yes you got the locations of the sensors correct).

If you had VAG COM you could run some tests with it to pinpoint where pressure is dropping but without it - start replacing the most common and cheap stuff first and work your way up.

 

I took your advice and ordered the high pressure sensor, and it just arrived in the mail today. But I cannot figure out how I will be able to get the old one off and the new one on. I can see it on the fuel rail in between the runners on the intake manifold, but it doesn't look like there is enough clearance to get at it from there. Do I need to pull the whole intake manifold off in order to access the pressure sensor? Or is there some other easier way to get it?

Is there a good guide on how to do it somewhere? I'm not having much luck via google.

 

I haven't had the "pleasure" of doing this myself yet but from the diagrams I found online I think you are correct that you would have to remove a few things to get there. I don't know if anyone else can offer some advise or help but you might have to start removing stuff until you get there.

I do have a Bentley repair manual on my computer at home (currently at work). If I remember I'll take a look at it tonight and see if they have instructions on how to replace that thing. I'll let you know what it states to do/remove to get to it.

 

I was actually able to get the old sensor out and the new sensor in late last night.
In case anyone else runs into this situation, this is how I was able to do it.
I loosened a few things to get better access but I did leave the intake manifold on. I removed the two T25 screws holding the hard fuel lines on top of the intake manifold to get better access from on top (this required pulling the pcv assembly to get to one of them)
I also removed the 10mm bolt and 10mm nut holding the coolant lines to the corner of the intake manifold by the oil dipstick and over the alternator. I also took tension off the serpentine belt and loosened the lower bolt holding the alternator in and removed the top bolt so I could swivel the alternator down a bit.
This gave me just enough access to get my crecent wrench behind the alternator and under the intake manifold to turn the pressure sensor 1/16th of a turn. Once it had come that far, I was able to turn it far enough by hand where I could access the clip to remove the wires to the sensor from the top of the manifold with a medium screwdriver. Once the wires were removed, I was able to remove the old sensor by hand. Getting the sensor out from behind the manifold without dropping it was a bit of a challenge, but not too hard. The assembly was pretty much the reverse, but in order to tighten the new sensor beyond hand tight, I couldn't get my crecent wrench on it so I used a 14?mm wrench on the plastic part of the sensor to get it a bit snugger than hand tight, but was careful not to tighten too much to not damage the new sensor.

After reassembly, it seems to be running better, but the check engine light was still on, and I was unable to road test it. I'll go to the auto parts store and read and clear the codes after work today and see if that fixes the limp mode problem.

 

You will have to clear the codes for sure - otherwise you will have to drive for 40 or 60 miles so that the ECU gets enough sensor data to see that the issue was fixed. It's much faster and quicker to clear all codes
I'm curious of the outcome so don't let me hanging...

 

I cleared the codes on my way home from work today and none of the codes stuck out to me so I didn't write them down. After clearing them, and starting the car the light came right back on and was complaining about the mass airflow sensor. I popped the hood, and dummy me forgot to clip the pigtail back into the sensor after reassembling the engine bay. It ran better and I cleared the code again.

Immediately after starting the engine, the ESP light came on and I read the codes again and it gave me P2294 Fuel Pressure Regulator 2 Control Circuit. I tried clearing it again, but it came right back when I started the car again. I made another stop on my way home and when I started the car again, no lights were on anymore. Hooray!!

Then within the first 60 seconds of celebrating by driving hard out of the empty parking lot, my celebration was cut short by the ESP and Check engine light coming back on. The car was still driving better than it had been since before I swapped the fuel pressure sensor, but not as well as it did before any of this started. It seems to have plenty of power at low revs and low speed, but it seems to taper off as the engine revs increase and when I try to accelerate up a hill. Also it seems like I have to push the gas pedal harder than I used to and hold gears longer to get decent acceleration.

Any ideas now?

 

Ok good start but unfortunately not the fix

Next thing on the list would be the HPFP (which includes the sensor, does not come separately) and a very close inspection of the camshaft/follower!

If you plan on keeping the car a long time or stay within the vw/audi family, you should really invest in a VAG-COM. That tool would be a huge help in running tests and pin-pointing what has failed.

 

What tests should I run on a VAGCOM? I don't want to throw a $300 part at the car without being sure it will solve the problem.
I'll see if I can find someone in my area who has a VAGCOM that would be willing to lend a hand in exchange for a 6-pack and it would help to know exactly what I need to look at since I don't want to waste anyone's time.

 

Here is a list of things you should run and check. If the only remaining code left is the 2294 you are looking at a possible N276 failure. That is the sensor on top of the HPFP and is not available separately
Anyhow check these things:

Special Notes

Check Fuel Pressure

North American Region (NAR) check TSB 2015153 (01-09-03 > 15-10-01 > 15-10-02), the Intake Camshaft might have a worn out Fuel Pump Cam.

Check the Fuel Pressure first.

Special Functions

Checking Fuel Pressure

Prerequisites:

Ignition ON
Engine ON (Idle)
System voltage at least 11.0 V.
Coolant Temperature at least 80 °C

[Select]
[01 - Engine]
[Meas. Blocks - 08]
Group 103
[Go!]
Field 1: Fuel Pressure (Low), Specification: 2800...7200 mbar
Field 2: Fuel Pump Adaptation, Specification: -1000...+1000 %

Group 140
[Go!]
Field 3: Fuel Rail Pressure (High), Specification: 25.0...110.0 bar
Increase the Engine Speed while checking this value, the Pressure has to rise with the Engine Speed.

Group 230
[Go!]
Field 1: Specified Fuel Rail Pressure (High)
Field 2: Actual Fuel Rail Pressure (High), Specification: 25.0...110.0 bar
Field 3: Deviation between specified and actual fuel pressure, Specification: max. 5.0 bar

[Done, Go Back]
[Close Controller, Go Back - 06]
North American Region (NAR) check TSB 2018183 (20-08-01) and verify the High Fuel Pressure Sensor (G247) Part Number

************************************************** *

As mentioned before Take a very close look at your camshaft, follower and HPFP...