Power Loss & P2293 - Fuel Pressure Regulator Valve (N276): Mechanical Malfunction

[betyouaint]

Ok... having trawled through the US Audi forums (I defected to the US around 5 years ago) trying to find a solution to my ongoing issues, I stumbled upon this forum. It seemed like there was a bit more knowledge flying around so figured I might get some better responses here.

Here's a brief history:

Car is a 2006 A4 2.0T with 120,000 miles, no mods
Experienced some power loss under hard acceleration which felt like a fuel cutout
Was getting a P2933 - Fuel Pressure Regulator Valve (N276): Mechanical Malfunction code.
Also getting a B310 code.
The dealer changed the high pressure fuel pump, camshaft and follower under an extended warranty
The B310 went away but the power loss and P2933 came back
The dealer diagnosed the in-tank fuel pump (working too hard)
Changed fuel filiter and the in-tank LP fuel pump
No change to the symptoms.

Below is a VCDS log from before the LP filter and pump change. Below that is a link to a longer log (.xls) after the LP fuel filter and in-tank pump change.You can see the HP pressure drops and corresponding values fro engine speed, LP pressure, throttle angle, LP pump, etc.

To me it looks like the problem is on the HP side, i.e. the LP fuel readings seem fine but the HP readings drop from over 100bar down to single figures. Despite these logs, both the dealership and forum posters keep suggesting the LP side. I can see how a problem with the LP feed would affect the HP feed but if anything, the LP value is at its highest when the HP is failing...!!!

Any suggestions what might be causing these issues?

http://www.legoheads.com/Log2.jpg
http://www.legoheads.com/Log1.jpg


http://www.legoheads.com/VCDSx1.xls (http://www.legoheads.com/VCDSx1.xls)

[Alan02]

You dont say why the Dealer changed the Pump etc. What was the diagnosis for them to be suspect? Worn ? Maybe the Fuel rail pressure regulator or sensor?

[gupsterg]

There is a VAG TSB / TPI where the 2.0 TFSI engine can get the following DTC logged:

P2293 control valve for fuel pressure, mechanical complaint

P1093 fuel pressure control, below limit
P0087 fuel rail/system pressure too low

Symptoms described as engine warning light on, often in connection with erratic engine operation or poor performance in the upper load range.

This is due to wear of the drive cam for the high pressure pump, the necessary pump piston lift is not reached causing rail pressure fluctuations. The wear on the cam often leads to wear of the bucket tappet base which may disintegrate.

What is your engine code?

[betyouaint]

Below are the original codes that prompted the dealer to carry out the TSB on the HPFP, follower and cam. Ignore the first one; I forgot to replug following an oil change... :Blush2:

Following this work, the P2293 has returned but rarely puts the CEL on, only once after frequent multiple occurrences. And like I said, changing the LP pump and filter made no difference either. I did see a thread related to a pressure relief valve that bleeds of fuel from the HP side when it exceeds either 116? or 126? bar depending on the car model. I also saw something regarding the HP fuel pressure sensor, which if faulty could fool the ECU into thinking pressure is low and causing it to cut power (similar limp to mode). If this is the case, it seems like it only fails when HP pressure is at or near its maximum.

I was wondering if either of these could likely be at fault in my case. In the later case, I may try to run the VCDS logger again and add the lambda value to see if it's genuine fuel cut or the ECU sticking its nose in...

Sunday,22,June,2014,08:53:07:46862
VCDS Version: Release 10.6.0

Address 01: Engine Labels: 06F-907-115-AXX.lbl
Control Module Part Number: 8E0 910 115 M HW: 8E0 907 115 D
Component and/or Version: 2.0l R4/4V TFSI 0070
Software Coding: 0104010A190F0120
Work Shop Code: WSC 08144 444 84095
VCID: 2B5E05F2B55F2644
3 Faults Found

005491 - Left Engine Mount Solenoid Valve (N144): Open Circuit
P1573 - 004 - No Signal/Communication - Intermittent
Freeze Frame
Fault Status: 00100100
Fault Priority: 0
Fault Frequency: 1
Mileage: 187418 km
Time Indication: 0

Freeze Frame
RPM: 740 /min
Load: 21.2 %
Speed: 0.0 km/h
Temperature: 69.0°C
Temperature: 49.0°C
Absolute Pres.: 1000.0 mbar
Voltage: 13.589 V

012555 - Low Pressure Fuel regulation: Fuel Pressure Outside Specification
P310B - 004 - No Signal/Communication - Intermittent - MIL ON
Freeze Frame
Fault Status: 10100100
Fault Priority: 0
Fault Frequency: 6
Mileage: 187483 km
Time Indication: 0

Freeze Frame
RPM: 994 /min
Load: 71.0 %
Speed: 6.0 km/h
Temperature: 33.0°C
Temperature: 33.0°C
Absolute Pres.: 1000.0 mbar
Voltage: 14.097 V

008851 - Fuel Pressure Regulator Valve (N276): Mechanical Malfunction
P2293 - 002 - Lower Limit Exceeded - Intermittent
Freeze Frame
Fault Status: 00100010
Fault Priority: 0
Fault Frequency: 1
Mileage: 187538 km
Time Indication: 0

Freeze Frame
RPM: 3113 /min
Load: 9.4 %
Speed: 90.0 km/h
Temperature: 88.0°C
Temperature: 34.0°C
Absolute Pres.: 990.0 mbar
Voltage: 13.716 V


Readiness: 0000 0000

[betyouaint]

This is going to require a diagnosis by someone who can look at the logs and determine what may cause this issue. And possibly someone who might suggest other parameters that it may be useful to log.

After doing some additional research, I ran some more logs after adding in the lambda value. As you can see below, the lambda value suggests the power loss may be a direct result of genuine fuel starvation and not (as I wondered) as a result of the ECU killing power due to an erroneous (low) HP fuel sensor reading. The only other time you see such a lean reading is when the throttle is almost closed on overrun and no fuel is being thrown in. That said, the ECU is definitely reducing the throttle when compared to the actual pedal position (not in the log) so it may also shut off the injectors due to the low fuel pressure...? Who knows...? It's hard to draw a proper conclusion without a better working knowledge of the system.

It's also worth mentioning, that the issue is intermittent and symptoms aren't necessarily consistent, i.e. the problem may or may not occur given seemingly identical circumstances. In addition, sometime the car jerks whereas other times it feels more like a limiter has been applied.

http://www.legoheads.com/lambda1.png
http://www.legoheads.com/lambda2.png

[betyouaint]

Still limping along with this issue. I've scoured the forums and seen many suggestions for some of my symptoms. I've seen a few people change the LP fuel sensor (thrust sensor), which has sorted their problems. In my case though, it seems that the LP side isn't the problem, the HP side is.

I've been wondering if the HP fuel sensor may be at fault? My thinking being that the apparent fuel cut is simply the engine going into "limp mode" upon detection of apparent low HP fuel reading?

Alternatively, I'm wondering if the fuel pressure relief valve is cracking open and pushing all the fuel back to the LP rail, effectively robbing the injectors of the pressure they need and slightly raising the LP rail fuel pressure (as seen in the logs)?

I could just spend the money and throw parts at it, and believe me, at this stage of the game I'm tempted to do just that. Problem is, how much money do I waste before I drop a burning rag in the tank...?

[Flash2]

Just a thought, but is there a measuring block for checking the fuel temperature?
If the ECU is seeing high fuel temp it may dump pressure from the rail to compensate for expansion. We all know how bad VW temp sensors can be.

Just a thought.

Jim.

[a8 tech]

Firstly a drop in rail pressure due to blockage needs to be eliminated so you will find there is valve under the inlet manifold on the fuel rail, remove it and replace it as this has a gauze filter which blocks.

https://www.google.co.uk/search?q=tfsi+fuel+pressure+regulator&rlz=1C1CHFX_en-GBGB565GB565&espv=2&biw=1517&bih=714&tbm=isch&imgil=u46j9D9VRM9i4M%253A%253BoiC07x7XAIIJmM%253Bh ttp%25253A%25252F%25252Fwww.audizine.com%25252Ffor um%25252Fshowthread.php%25252F473448-Fuel-Rail-Pressure-Regulator-Valve-Install-Replacement&source=iu&pf=m&fir=u46j9D9VRM9i4M%253A%252CoiC07x7XAIIJmM%252C_&usg=__-n4d_UyC_BLXQ18clD7SMGfUbjE%3D&dpr=0.9&ved=0CDsQyjc&ei=GgdtVKLvOsjmaJv8gtAH#facrc=_&imgdii=_&imgrc=u46j9D9VRM9i4M%253A%3BoiC07x7XAIIJmM%3Bhttp% 253A%252F%252Fhpfpupgrade.com%252Fimages%252FVW_Au di_Rail_valve_1.JPG%3Bhttp%253A%252F%252Fwww.audiz ine.com%252Fforum%252Fshowthread.php%252F473448-Fuel-Rail-Pressure-Regulator-Valve-Install-Replacement%3B1600%3B1200

Try to use a fuel pressure tester to calculate accurate pressure.

[betyouaint]

Firstly a drop in rail pressure due to blockage needs to be eliminated so you will find there is valve under the inlet manifold on the fuel rail, remove it and replace it as this has a gauze filter which blocks.

Try to use a fuel pressure tester to calculate accurate pressure.


From what I understand, this valve is a regulator which returns fuel from the HP rail to the LP side. If this was blocked then it would fail to return fuel to the LP side potentially resulting in excessive pressure on the HP rail, not a drop in pressure. The only way I see this valve being at fault is that it is opening (possibly due to excessive pressure) but opening too much and for too long, effectively dumping all the pressure to the LP side instead of "regulating the HP rail fuel pressure. Am I missing something?

[betyouaint]

Based on a mix of ease of task, probability of part at fault and price of replacement part, I've decided that the HP fuel sensor shall be the first item to replaced...

Fuel Pressure Sensor, 2.0T (0261545050) (http://www.urotuning.com/ProductDetails.asp?ProductCode=06J906051D_Bosch)

Next will be the FRV... and then the LP fuel pressure sensor.

[betyouaint]

Okay... so yesterday I changed the HP fuel sensor for this replacement...

Audi > A4/S4 > B7 A4 > Engine Performance > 2.0T > Fuel System (http://www.urotuning.com/Fuel-System-s/2463.htm)

The replacement item was shorter than the original which seemed a little odd but it was the one listed for my car.

Car seemed okay for the first couple of miles but then when I really booted it, the problems returned worse than ever. Now I get the same engine code only now it puts the CEL on. In running VCDS (see log snippet below with added fuel pressure delta column), the HP fuel sensor reports no more than 90 bar (actual) on the HP fuel rail despite the specified being around 110 bar. For the range 0 - 90 bar, the actual value matches specified value pretty closely but beyond 90, the sensor stalls at 90 bar. The car has almost no power and 0-60 comes up in around 30-40 seconds. Not really much fun for my 80 miles round trip commute.

Now, either the new sensor won't read above 90 bar (even though it seemed fine for the first couple of miles), or alternatively, whatever was causing the original intermittent drop in fuel pressure has started to fail more consistently, quite possibly the fuel regulator valve, as a result of my vigorous test driving. I already have on order and hope to receive it in the next couple of days.

Tomorrow, I plan to switch the HP fuel pressure sensor back to the original and see if that gives me readings over 90 bar. As you can see from the original logs, the readings with this sensor showed readings up above 90 bar and were pretty consistent with the specified values until the intermittent power loss when the specified was over 100 bar and the actual could drop as low as 6.4 bar. I'm hoping that once reinstalled the original sensor mirrors the behavior of the new one, confirming that this is not a sensor issue and is more than likely a failing pressure regulator valve.

I've also notice that the LP side is hitting high 6's which I'm wondering if has something to do with the influx of high pressure fuel from the HP rail to the LP rail via the pressure regulating valve. Just a theory but it kind of fits...? Of course, it could just be the LP pump responding to the HP fuel situation by ensuring it is delivering enough fuel.

http://www.legoheads.com/HP-LP_New_Sensor.PNG

[betyouaint]

This morning, I replaced the new sensor with the original and the symptoms are now back to pre-new sensor. New logs (below) show the original sensor reads (or seems to read) 120+ bar and the car seems much happier than with the new sensor. Wrong replacement sensor I guess? It doesn't look the same and none of the numbers match.


From earlier logs containing lambda information during low HP fuel readings I have no solid grounds for suspecting that the HP pressure sensor be at fault as fueling seems okay for the the most part. This I believe confirms that the replacement sensor is definately the wrong item and tops out at 90 bar.


Never easy to be certain as the engine management corrects for out of tolerance conditions effectively masking the symptoms that might help in diagnosis.


The other thing I'm noticing is that the HP rail fuel pressure is exceeding its specified value just before the symptoms occur, e.g. specified of 109 bar, actual of 126 bar. The specified and actual track pretty well throughout the range, usually within 1 bar. Only around the time the problem occurs do they part ways and the control loop starts to fail. I'd be interested to see logs from a healthy car comparing these values under high acceleration.




http://www.legoheads.com/HP-LP_Old_Sensor.PNG


http://www.legoheads.com/HPsensors01.jpg


http://www.legoheads.com/HPsensors02.jpg

[betyouaint]

OK... I've been mulling this one over a bit more. Something that A8Tech was talking about regarding a blockage in the PRV got me thinking. I noticed that in most cases, when the power loss occurs when the actual HP fuel pressure exceeds the specified pressure. I also read something that when people have tried to fit an uprated PRV to a standard tune they have had issues. It was suggested that this was because the tune detects the over-pressure and backs everything off. In my case, I have a standard PRV but if it is blocked or not opening at the designated pressure then it's possible that the engine management is backing off due to the same over-pressure scenario.

I have a new PRV in hand and will hopefully get around to changing it out this weekend. I'll let you know...

[betyouaint]

PRV changed this morning with the help of my 9 year old daughter (still in her footie pajamas) and her tiny hands (see below). I did a quick test run (with logs) and all seems good but I'd like to run a longer test to be sure.


Looking back at the logs, the actual and specified values tracked really well and the actual rarely went over 110 bar. There was one instance where it hit 126 bar for a single frame but that was off throttle and so I didn't notice any power loss symptoms. At no time was the actual significantly lower than the specified with the maximum negative delta being -3.2 bar for a single frame.



In your case, I think that you’re on the right track with the PRV, but I think that your logic for why is wrong.


I doubt that the ECU is deciding that the rail pressure is too high and then backing everything off. The reason I think this is that if the PRV remained shut the actual rail pressure would stay high and not drop like you're seeing.


My thinking is that we both have a lazy PRV that doesn’t instantly re-close when the pressure drops back to lower than its “crack” setting.


Yeah, my initial thinking was that the PRV was lazy on both opening and on closing and this may indeed be the case. It was the post (see PRV change DIY in tech forum) that got me thinking about the ECU backing things off. There's no doubt that at times the symptoms I've experienced have resulted in the car going into limp mode and have not simply been due to fuel starvation. In the case of this ECU back-off theory, my thinking is that the drop in fuel pressure is a combination of the ECU regulating the pressure with the electrically actuated fuel pressure regulating valve in the HPFP and the natural consumption of the engine which is still taking it from the HP fuel rail and firing it through the injectors into the cylinders. I have no idea if this really makes sense (without knowledge of the control loops in the program itself) or even if the fuel usage would allow an almost instantaneous reduction in pressure from 126bar down to 6.4bar?


On the plus side, either theory suggests that the PRV is at fault.


I'll report back after a longer test run...


http://www.legoheads.com/kidfixx.jpg

[betyouaint]

I went for a longer test drive last night and did manage to produce a couple of small hiccups during a dozen or more high throttle runs. Nowhere near as bad as it was but there's still definitely something amiss. I didn't run logs and I haven't checked for codes but there is no CEL on. Also worth noting, it was very cold last night, well below freezing, which may have a bearing on the issue a previously discussed.


I'll try again tomorrow and run some logs.

[Burt Macklin]

Subscribed. Very eager to hear your resolution. I am having the same issue. A side note on some of my issue's background. I took my 2011 Tiguan in for a NHTSA safety recall in reference to air bubbles in the fuel line, or something silly like that. The "fix" was increasing the fuel pressure to somehow prevent bubbles from occurring. About a week after that service was done I encounter the same loss in power and P2293. Only symptoms are check engine code P2293 and loss of power. It feels as if there is no boost. Otherwise the vehicle has no drivability issues nor observed changes in MPG. Please keep me updated!

[betyouaint]

Still no resolution...


Longer tests runs saw the return of the original symptoms and I've posted a bunch of logs below. The green highlights show where I was above 70% throttle, the red shows where actual HP fuel pressure was significantly lower than specified HP fuel pressure and . Pink shows where actual exceeds specified.


I've tried 3 different HP fuel pressure sensors, the original, a replacement that was the wrong PN and only gave a maximum reading of 90 bar, and a used part from ebay, which was the same as the original. I doubt this is the culprit but have a new one of the correct PN on its way.


I have also ordered a LP fuel pressure sensor (thrust sensor) which is the last thing on my list. After that, it's back to the drawing board.

http://www.legoheads.com/2014-12-08-01.PNG
http://www.legoheads.com/2014-12-08-02.PNG
http://www.legoheads.com/2014-12-08-03.PNG
http://www.legoheads.com/2014-12-08-04.PNG
http://www.legoheads.com/2014-12-08-05.PNG

[betyouaint]

And for Burt... here are the pictures of the mechanical PRV I changed, which is different from the electro-mechanical pressure control valve within the HPFP.

http://www.legoheads.com/PRV01.jpg


http://www.legoheads.com/PRV02.jpg

[betyouaint]

G410 thrust sensor (LP fuel sensor) replaced. Symptoms still apparent.


A brand new HP fuel sensor (correct PN) arrived yesterday. I'll be fitting later today but not sure when I'll get chance for an extended test drive.

[CupraDave]

Hey buddy, I have had a similar problem with my Seat Cupra K1 I think it's going to be pretty much the same car running standard 240bhp, Loss of power when I put the foot down, took it home got the same code as you, checked the HPFP and it had a crack in it, replaced the HPFP but now the car won't start at all, you had any joy with any of the other parts you changed? I've been trying to sort this since the 1st of December, absolute nightmare! Not handy either when I just forked out 260 quid for a part that hasn't resolved the issue.. I have taken out the coil packs and spark plugs to see if there was anything indicated there that wouldn't be starting the car but everything seems fine, getting to the end of the road where this is going to turn into a bonus round of Street Fighter! Haha, hope your car is back running again mate, any advice would be great, cheers.

[SammoVWT]

I have seen cases of solenoid driven valves such as injectors fail to open because the pressure is too high, not sure if this is the case but. I feel its worth keeping in mind. Interesting read though, hope you get to the bottom of it.

Also there may be a good reason why the rail is rated to 110 (safety rating as in maximum allowed pressure before it pops).

90 may even be the correct pressure. if the range is supposed to be from 0-90bar etc.

Similar principle in fridge, the pipework may be able to withstand 50bar for example. but the system runs at 25bar as a design and the 50bar max is incase some valves let go.

It looks to me like you still have an over pressure issue from looking at your previous posts/logs. For whatever reason, something in your car is thinking the fuel pressure is low, and forcing the pump to run more OR the pump is knackered (and blockages as have been previously mentioned) OR pressure is normal and thinks is high and backing off.

I would prove that nothing is providing a restriction. Have you serviced your injectors at all? Might be worth checking the filter baskets in them.

If you had some dirty fuel it could well have made your PV dirty and injectors, both of which can cause a rise in pressure.

You dont always get a code with a faulty sensor, they can go out of spec. Seen this in the field more times than I've had hot dinners. A lot of the automotive style sensors for pressure are similar to the ones we use at work. Infact some of them are 'automotive' pressure transducers.

Looking closely at the logs, it looks like the pressure drops off right around when it reaches the 110.0 bar max, are you sure your HP sensor is good?

When dealing with high pressure systems, its very common for safety procedures to be put in to reduce extreme pressure. In this case it might well be backing off the pump if the actual pressure is 90 and the reading is 110.0 so could be backing off due to erroneous sensor range.

Have you got a gauge you can put on the fuel line to check real pressure?

If sensor is definately brand new with no problems, it might be the loom going into that set of sensors.

[betyouaint]

Think I may have found the problem.

When checking for codes (every few days over recent months) I had occasionally seen an intermittent P0341 cam position sensor (G40) code. It didn't match (timewise) up to the P2293 code and they often appeared completely independently so I never made any connection. However, as I'd changed pretty much everything I could think of (without starting back at the HPFP) I figured I should at least take a look at the cam position sensor and at the very least, get rid of that code.

008851 - Fuel Pressure Regulator Valve (N276): Mechanical Malfunction
P2293 - 002 - Lower Limit Exceeded - Intermittent
Freeze Frame
Fault Status: 00100010
Fault Priority: 0
Fault Frequency: 2
Mileage: 205445 km
Time Indication: 0


Freeze Frame
RPM: 2302 /min
Load: 63.9 %
Speed: 104.0 km/h
Temperature: 91.0°C
Temperature: 6.0°C
Absolute Pres.: 980.0 mbar
Voltage: 13.970 V


000833 - Camshaft Position Sensor (G40): Implausible Signal
P0341 - 008 - Implausible Signal - Intermittent
Freeze Frame
Fault Status: 00101000
Fault Priority: 0
Fault Frequency: 1
Mileage: 206101 km
Time Indication: 0


Freeze Frame
RPM: 5352 /min
Load: 100.0 %
Speed: 112.0 km/h
Temperature: 90.0°C
Temperature: 8.0°C
Absolute Pres.: 980.0 mbar
Voltage: 13.843 V

When I pulled the sensor, I found that the tip was covered in fine metal shavings (like an oil mag plug) which I suspect came from the worn cam and follower that was the first repair by Audi just over 10,000 miles before. I figured this would likely affect the magnetic field critical to the hall effect measurement of the cam position and would likely explain the P0341 code. I cleaned it up and refitted it. Within the first mile I got the following code which put the check engine light (MIL) on.

000010 - Camshaft Positioner (Bank 1 Intake): Slow Response
P000A - 008 - Implausible Signal - Intermittent - MIL ON
Freeze Frame
Fault Status: 10101000
Fault Priority: 0
Fault Frequency: 1
Mileage: 206529 km
Time Indication: 0


Freeze Frame
RPM: 1303 /min
Load: 43.9 %
Speed: 0.0 km/h
Temperature: 17.0°C
Temperature: 3.0°C
Absolute Pres.: 980.0 mbar
Voltage: 14.097 V

I reset this code - which I suspect was the engine management readjusting to the new (correct) CPS reading - and did a few long test drives with plenty of hard acceleration/high speed runs. The P000A code didn't come back and neither did the P0341 or P2293. Also, I've had no recurrence of the power loss symptoms. After covering around 400 miles I'm getting more confident that my issue is fixed.

I can only speculate on why a contaminated CPS might cause the HP fuel pressure to drop from 100+bar down to 6.4bar, but can make no real educated connection between the two. To be honest, I'm just glad my car is driving normally for the first time in over 6 months.

[CaliB7]

Think I may have found the problem.

When checking for codes (every few days over recent months) I had occasionally seen an intermittent P0341 cam position sensor (G40) code. It didn't match (timewise) up to the P2293 code and they often appeared completely independently so I never made any connection. However, as I'd changed pretty much everything I could think of (without starting back at the HPFP) I figured I should at least take a look at the cam position sensor and at the very least, get rid of that code.


When I pulled the sensor, I found that the tip was covered in fine metal shavings (like an oil mag plug) which I suspect came from the worn cam and follower that was the first repair by Audi just over 10,000 miles before. I figured this would likely affect the magnetic field critical to the hall effect measurement of the cam position and would likely explain the P0341 code. I cleaned it up and refitted it. Within the first mile I got the following code which put the check engine light (MIL) on.


I reset this code - which I suspect was the engine management readjusting to the new (correct) CPS reading - and did a few long test drives with plenty of hard acceleration/high speed runs. The P000A code didn't come back and neither did the P0341 or P2293. Also, I've had no recurrence of the power loss symptoms. After covering around 400 miles I'm getting more confident that my issue is fixed.

I can only speculate on why a contaminated CPS might cause the HP fuel pressure to drop from 100+bar down to 6.4bar, but can make no real educated connection between the two. To be honest, I'm just glad my car is driving normally for the first time in over 6 months.


Hey betyouaint, I'm trying to use your old work to debug a problem, I think I may have a similar issue. I have the P2293 (n276 mech. malfunction) code but have already replaced the pump, checked all electricals, and made sure my tune wasn't the issue, so I've started to expand where I think the problem may stem from, and a camshaft position sensor giving incorrect data to the system would DEFINITELY make the HPFP malfunction, the timing would be off between the piston trying to pump fuel pressure up and the internal check valves that close to maintain the pressure while the piston is dropping each cycle.

Are there any other symptoms you had that cleared up when the CPS was cleaned up? I also have a mechanical clicking sound coming from somewhere in the valve train that I can only hear on overrun, and it seems easy to believe that the position sensor could be related.

Thanks!