I've had a low fuel pressure fault going on and off periodically for a few months now. Originally had the code checked but it had already gone off be the time I made it into the shop. They were reluctant to do any work with the light off and the car running fine so I put it off until my next scheduled maintenance. Light continued to go on and off randomly, can't seem to pick up any pattern

Took it back in and here is what they tested:
"Monitored readings from fuel pressure sensor. Found readings fluctuate out specification. Suspect sensor is faulty or fuel pressure is not correct. Tested operation of fuel pressure sensor and it's OK. Performed output test of fuel pump and it's OK. Found fuel pressure is now within specification. Symptom is intermittent so tests are so far inconclusive."

Anyone experienced something similar? Any ideas? I'm reluctant to just replace the sensor, or at least not until I know a little more.

Codes are:
1) "Low pressure, fuel pressure regulation" - P129 E
2) "Low Pressure fuel regulation" - P310 B

Thanks!!

 

I'm guessing it wasn't a dealer tech because they gave you all that information? It's pretty great that you got all that FYI - most mechanics just charge for diagnostics and then propose replacing a bunch of parts. The wait-and-see approach is welcome and refreshing!

If it was a dealer, they would have done the testing per the TSB on the thrust sensor (G410). My understanding is that some people have had these replaced under extended warranty, so that might interest you.

If the sensor is original, the part wasn't very good and will likely fail eventually, so at $36 and a few minutes to replace, I'd just get a new one and save the trouble of the dealer and future headaches/uncertainty. At the dealer you might spend 5 times that on diagnostics only to get nothing done...

Before you go to that trouble though, have you thought about replacing the fuel filter if it hasn't been done yet? The code in the sensor TSB is P129F, which is actually "pressure too high". You've got P129E, which is "pressure too low". P310B is just "outside" the tolerance of what it wants, which we already know (think) is too low in your case. A fuel filter that was somewhat restricted would operate normally at moderate flow but then impede proper flow at higher demands. In other words things could 'check out' but still be amiss. I think the filter has the return line in the filter housing as well, though I'm not sure if that's pre or post filter. If pre-filter, the excess flow from the restriction just goes back into the tank and won't even try to "push" its way forward.

The filter is also cheap, probably available locally, and very easy to replace (just push the fuel lines in while pinching to unlatch/release, they won't pull straight off!... and have a small pan to catch the bit of fuel that will come out, work in ventilated area, etc...). If you're really cheap, (a) you shouldn't have bought an Audi, but (b) you can even remove the filter, swish it around, and dump the fuel out of the INLET side. You'll see all the crap and dirty fuel that comes out and immediately want to put a new filter in, but if for some reason it looks crystal clear, you can hook it back up and move onto the sensor (i.e. return the filter).

 

Def. not a dealer tech.

I appreciate the feedback, sounds like two good options. I'm not afraid to spend money on the car, but I hate just throwing money at a problem without knowing exactly what it is.

Any idea where I could find DIYs on either of those fixes? Looked around a bit and didn't see anything.

thanks again!!!!

 

Not an endorsement of any of these DIY's - I just ripped into both jobs without any prior research. Do the fuel filter first because it's probably a good idea either way. Replacing mine didn't fix my P0089 code but after 100K it was probably overdue!

Fuel filter: DIY: Replacing the Fuel Filter

Audi B6/B7 S4 DIY: Fuel Filter

The thrust sensor is even easier - IIRC you just remove the PCV hose, disconnect the harness plugged into the sensor and screw it off. I think I used a big *** ratcheting wrench to get it off quickly, but I'm sure you could work it off with something else.

 

Here's a video on the fuel filter from another audi. Ours is easier to access fortunately, but this should show you what to expect in terms of dripping fuel!

 

Thanks for the advice and DIY links...finally got around to doing everything last week, everything installed really easily and so far so good on the check engine light.

Really appreciate the help!!!

 

Great! Report back if it actually fixes it long term and maybe you'll help someone coming across the same situation in the future. It's also good to hear you found it easy and hopefully that will encourage others to undertake the maintenance on their own as well.