Understanding OBD

Under construction

Originally I had planned to talk about OBD Eleven here, but for the time being I am just going to describe OBD interface and how it works...

OBD Protocol:
This page by Klav Karr is very complete. Check all the info, not only that page, like the hardware level info and the standard fault codes.
Link
Wikipedia OBD
Wikipedia PIDs (OBD Parameter IDs)

This guy explains what adaptation, long coding, etc... is. Then posts a lot of the info corresponding to all those codes. Notice that OBD calls

Somehow there is this term out there about "measuring blocks". Not sure if it is universal or a function name on the VCDS software (from Ross-Tech). Regardless, what matters is that all the info you can pull from the car through OBD is divided in groups of 4 registers. Somehow in OBDEleven they talk about "channels" instead of groups. Regardless, each group or channels has 4 values (each for one thing, and not always all are used). Ross-Tech info on standard measuring block group. An example of key groups for my fuel cuts debugging (can see more of the word usage here) is listed below. I highlight in red the ones that I am finally plotting for debugging:

1. Group 1:
1. RPM
2. Group 2:
1. RPM (yes, again, just to illustrate that there can be repeated values)
2. Load (%). I believe this refers to the car engine load (?)
3. Group 3:
1. N/A
2. N/A
3. Throttle (%)
4. Group 103: (notice how the previous link actually has different stuff in here, as I think there are no standards...)
1. Fuel pressure (Low). Low means low pressure, not low limit or something like that. It is basically the one produced by the in-tank pump (lpfp).
5. Group 106:
1. Fuel pressure (High). High here refers to the high pressure and this value should be the same as the group 230 #2.
2. Load (%). The word load applies to different engines... In this case it is referring to the LPFP and it has nothing to do with the group 2 #2. As these pumps are usually PWM pumps, it also refers to the duty cycle of the control signal.
6. Group 230:
1. Fuel Rail Pressure: Commanded Fuel Pressure (aka specified). Fuel rail refers to the high pressure circuit, the one hitting the cylinders. Commanded because is what the ECM wants to get but controlling the hpfp.
2. Fuel Rail Pressure: Actual Fuel Pressure.
3. Fuel Rail Pressure: Fuel Pressure Difference (between 1 and 2). You can just compute this but I guess they provide it in case you want to plot that for debugging, real time...
7. Group 231
1. Fuel Pressure: Commanded Fuel Pressure (aka specified). Usually, if nothing is said, fuel pressure refers to the low one. Sometimes they say "Low" (as used above). This number should be same as group 103, #1.
2. Fuel Pressure: Actual Fuel Pressure.
3. Load (%) refers here to the load of the in-tank fuel pump (lpfp). Same as group 106 #2...

Good news is that you can't break anything by looking at this. Looks like OBD computer gives not only the register but also what the units are. So, the software can try to interpret the Byte (?) it gets. Need to learn more about the OBD memory. It also looks like these may not be standard across vehicles. Probably some are but many are not.

In OBDEleven, you access it by going to the right control unit and clicking in Live data. Once there you can also plot it (click the little graph icon on top). It is annoying because I don't think you can save the graph settings so every capture you have to retype it. Got to understand this better...

Can you really buy an OBD reader for $2?!?
The car hacker handbook

OBD for VW GTI MKV

This post is under construction. Probably don't want to spend much time on it...

Trying to find what to buy to monitor my HPFP or errors (see other posts on this), although now the car runs nice (after the spark plugs job. Update: it doesn't, see debugging here...). Here is what I learnt:

1. VCDS® HEX-V2® Enthusiast: The VW tool by excellence. $200. Uses USB.
2. BlueDriver seems to be well recommended, but not sure it allows me to program the car. It works with many cars. Free app but can't be accessed from other apps.
3. OBDEleven: lots of people says this is good. Get the PRO for about $80 that allows to program the car... Seems to work only on VW family cars... (Audi, Skoda...). Nice app, you can do everything you want yourself at low level but if you want click-only easy type of mods got to pay. I bought this one as it felt like a good trade-off. Almost regretting not to spent the $200 on the #1 but it's doing ok. My review/explanations here. 
4. Open source: but still hardware is expensive because uses some expensive MCU board... Still, the info on that site can teach us how to do ourselves one, if one day we want to.

I may update this back based on my learnings... Just putting it out there.

GTI VW MKV P0087 P2293

Very quick entry in case someone struggling with those codes...

1. As you already found on the web, this could be a cam follower going bad. In the MKV people says that this can happen quite often and then the whole camshaft has to be replaced (because the high pressure fuel pump (HPFP) eats away the cam. That's a $1k job in the dealer + all the other stuff to remove the metal debris from the car. Not nice. So, if you get this code or EPC light and the code is not going away go straight to the dealer. Usually this issue also trigger limp mode (reduce engine power) for safety.
2. Nevertheless, in my case code came and disappeared after turning on/off the car. Still I went to dealer and the cam follower was ok. Actually they even didn't know what I was talking about when I told them that I read it was an issue with the car. They even didn't have one in stock! Anyhow, they told me there was an error code with the HPFP solenoid (2294) BUT I actually didn't do the job (they said it would cost $550 + $180). They still wanted to charge me the $180 even when they already had the pump out! Instead of putting the old pump in I ask them to put the new one in but they didn't want to do that for the same price as changing the follower >.>
3. Anyhow, I was planning to do it myself as it looks quite easy (google it...). Nevertheless, I first replaced my spark plugs (I had got a code back 6 months ago that never came back). And boom, car seemed to work beautiful... Probably because that needed fixing too. But...
4. Update: few days later I lost power several times in high revs. No engine lights up, though. I am going to get the OBD reader to see if I got any codes...
5. My dad said that it could be the fuel filter (actually car 110k miles and I don't think I ever changed it). Maybe in some routine maintenance long ago, but don't recall. The piece is WK69 6.6bar (although for some mistake I ended up using a 6.4). This guy explains what the 3 pipes do on the filter and what is the regulator. So, found this about how to change it:  
1. Youtube - It is for an MK6 but really well explained.
2. Forum write up - I think the best for those hoses is to remove the two rear clips, then remove the filter from the holder. That allows for better finger access to the other clip. And let the car sit overnight and do not open the doors in the morning (as that primes the pump and increases the pressure). Use eye protection! Also I would put a piece of cloth around the connection so that muffles any squirting.
3. https://forums.vwvortex.com/showthread.php?5537643-Fuel-filter-change-on-07-MK5
6. One guy says to put the ignition key on the AC position (power on without turning on the engine?) few times for 30s to purge the fuel line. 
7. Called a different dealer and they charge me $495 for the pump! Wonder how come they have different prices but anyhow, the Hitachi one on Deutsche Autoparts is $235!
8. This has a nice explanation of the P2293 and P2294 codes. Only thing is that it seems to say that with voltage, the regulator opens increasing the pressure but a video below says the opposite. Maybe this is talking about the LPFP and the video certainly is talking about the HPFP.
9. The 2293 is the code that I see all the time. The 2294 is the one that the dealer saw. Not sure I still have it now. So, I still don't want to buy the hpfp till sure. Notice how, for the 2293, they say that a clogged filter could be the reason. People also points to the LPFP or its control module. For the 2294, they said to check the wiring going to the fuel pressure regulator as some times animals chew on it! AMAZING. I saw an empty shell of a nut cracked open inside. This could totally be the reason. Another clue may be that temperature doesn't seem to make a difference (?). All days were actually very cold but things didn't look worse with warmer weather.
10. Nevertheless, found this ross-tech link of all the codes and it clearly says "Fuel Pressure Regulator Valve (N276): Mechanical Malfunction". As possible solutions does mention fuel filter, for instance:
1. Check Measuring Values for Fuel Pressure
2. Check for bent/squeezed Fuel Lines
3. Check Fuel Pressure System for Leaks
4. Check Fuel Filter & Filter in Fuel Pump
5. Check Fuel Quantity supplied by the Fuel Pump
6. Check Pressure Limiting Valve installed on the high pressure fuel rail when applicable
11. How about the P0087? 
12. N276 valve is the solenoid (fuel pressure regulator). In this link says that ohming it out should show 25 to 30 Ohms. See THIS FULL REPAIR MANUAL for more details. It tells you also how to follow the control wire back to the ECU.
13. The hpfp can get to 120 bar (normal is between 30 and 110) while low pressure is about 6 bar. Here says that low pressure rail should be 0.5 to 5bar. I wonder if this is reported somewhere in the OBD. 100 psi is about 6.9 bar.
14. Fuel trim explanation in detail, another level up.
15. Return vs Return-less fuel systems. Mine is probably return-less because of emissions.
16. How hpfp system works and how the pump itself works. Notice here that when no voltage is given to the regulator the pressure actually drops (i.e., solenoid must be closed not letting fuel into the HPFP). This is the opposite of what the video says.
17. Found in the manual how to check the fuel delivery system
18. Coding. Checking fuel pressure codes here.
19. Found a kick-ass document describing the whole fuel system: Service Training, Self-study programme 334, The fuel system in FSI engines. 
20. Update: changed the fuel filter. Car sounds better. Codes still there but they are from yesterday when I was messing with the hpfp and the intake flow sensor was disconnected. Reset them. Now measuring pump pressure with OBD2. Codes came back. Got a new one too: P310B. This actually now seems to point to the LPFP! I guess changing the filter did something? As it can be seen in the video, the duty cycle should be lower but I am getting very high although the pressure is good
21. With OBDEleven one can click on gages to see a value, but if what you want to see it's not there, you can go to the control unit. I created a separate post on OBDEleven.

Will post back after I do this change and see if my car goes back to normal...
Fuel system of the FSI engine.


Check your lpfp like this
P310B

1. This guy says that "Generally lpfp issues you have stalling, while hpfp you can still limp it around". That would mean is my HPFP

They say you should hear it click
Can the HP change so fast? I guess so. The other thought would be the sensor, but why the cuts would happen related to the acceleration. A sensor fail should be uncorrelated with that.
It is pretty clear that the load on the LPFP goes to 100% only on reaction to drops on HP, but not so clear on how to get it out of there. Why gets stack

Drive next day after fix
Drive to dinner Everything looks nicely in place. LPFP between 30 and 40%. Most of the drive on secondary streets.
Drive to run. First and last part on secondary streets. Middle in highway.


My forum post

The post on the MKV forum

Nice doc on GTI FSI engine
P310B causes
Another good video of how GDI (gasoline direct injection) works
Sponsors that helped create some of the videos I watched:

• FCP Euro: cool diagram of the pump
• Deutsche auto parts

Humble Mechanic

Nice place to check vw car diagrams