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OBD Scanners Discussions on using On Board Diagnostic (OBD) scanners/ Diagnostic Equipment related to TDIs

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Old January 26th, 2008, 16:27   #1
seftonm
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Default Scangauge Boost Gauge and General XGauge Coding info

With help from CarlD and 2way on the cleanmpg forums I now have an XGauge that comes close to showing the gauge pressure of the MAP (turbo boost) instead of the absolute pressure (atmosphere plus boost). The coding is as follows:

TXD: 68 6A F1 01 0B
-or-
TXD: 07 E0 01 0B for CAN-bus vehicles. The new TDI apparently won't report MAP and therefore this won't work.
RXF: 04 41 85 0B 00 00
RXD: 28 08
MTH: 00 91 00 64 FF 71

This will get the absolute MAP pressure, convert it to PSI, and subtract a constant, which in my case is the average atmospheric pressure in Brandon. Subtracting the average atmospheric pressure gives a close idea of how much boost the turbo is making. If a drive has large changes in elevation or pressure the gauge can be out by a few PSI.

The last four characters in the MTH field are an addition. To subtract, you must add the 2's complement of the number you wish to subtract. In this case, the result is being divided by 10, so the number being subtracted must also be multiplied by 10. For example:
I want to subtract 14.3 PSI. 14.3 * 10 = 143 = 008F in hex. 2's complement of 008F is FF71. The last 4 characters in the MTH field are therefore FF71 in my case.

Of course, pressure varies with elevation so you may need to subtract a different value. Here are the 2's complement representations of common values for pressure:
12.0 -- FF88
12.1 -- FF87
12.2 -- FF86
12.3 -- FF85
12.4 -- FF84
12.5 -- FF83
12.6 -- FF82
12.7 -- FF81
12.8 -- FF80
12.9 -- FF7F
13.0 -- FF7E
13.1 -- FF7D
13.2 -- FF7C
13.3 -- FF7B
13.4 -- FF7A
13.5 -- FF79
13.6 -- FF78
13.7 -- FF77
13.8 -- FF76
13.9 -- FF75
14.0 -- FF74
14.1 -- FF73
14.2 -- FF72
14.3 -- FF71
14.4 -- FF70
14.5 -- FF6F
14.6 -- FF6E
14.7 -- FF6D
14.8 -- FF6C
14.9 -- FF6B
15.0 -- FF6A

Here are two sites to computer atmospheric pressure based on elevation, courtesy of Bayou_Flyer and Mrrogers1:
http://www.turblex.com/altitude/index.cfm
http://www.grow.arizona.edu/Grow--Gr...ResourceId=214

I was also given help for XGauge programming and OBD-II PID's. The programming guide is at http://pics.tdiclub.com/data/500/XGauge_Coding.pdf
and OBD PID's are at http://en.wikipedia.org/wiki/OBD-II_PIDs


Other useful codes: (PM me and I'll add to the list)

Water temperature for newer vehicles where the default water temperature gauge won't work:
TXD: 07DF0167
RXF: 04410567
RXD: 3008
MTH: 00090005FFD8 (or 00010001FFD8 if you prefer celcius)
NAM: WTR

Last edited by seftonm; August 29th, 2011 at 21:24.
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Old January 27th, 2008, 09:21   #2
Reichard
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Excellent! MAny thanks for the writeup! Took about two minutes to add.

Now if ony I could get a torque xgauge displayed. I have logs of mine from my vagcom and it would be a great addition.
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Old January 27th, 2008, 15:59   #3
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Great tested and works great, only thing is if we could give the map data to update faster. It's a little slow
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Old January 27th, 2008, 17:40   #4
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Have you tried increasing the ScanGauge update speed?
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Old January 27th, 2008, 22:13   #5
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I was hoping someone would come up with this. As soon as I added distance to empty as an x-gauge, doing the same for the map was the first thing I though of. Very shortly, I am going to put my coat on and do this.
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Old January 27th, 2008, 23:24   #6
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Just came in from the cold. Seems to work fine. Didn't take it for a drive yet, but I did start it. Slight negative boost at idle ( .6psi and I expected that ). Will report if anything funky, but I expect not. Thanks again !
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Old January 28th, 2008, 04:22   #7
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Quote:
Originally Posted by seftonm
Have you tried increasing the ScanGauge update speed?
I can't notice a difference in the update speed settings at all.
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Old January 28th, 2008, 12:45   #8
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I don't think that will make a difference anyway. The ECM only samples so fast.
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Old January 28th, 2008, 13:49   #9
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I thought the Mk5's used a CAN bus, which is often fast enough to use the fast update speed. If there is no difference, you should probably slow the update speed back down to avoid possible errors.
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Old January 28th, 2008, 14:11   #10
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Seftonm, your original post sounds like you did the XGage upgrade your self. Is this the case? If so can you share how you did it, or point those of us with the pre-XGage somehwere to help?

The ScanGage II web site says you have to send the unit back for the upgrade. I do not want to go without the ScanGage, especailly when I am pulling a trailer.

Thanks...
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Old January 28th, 2008, 14:22   #11
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Quote:
Originally Posted by seftonm
Have you tried increasing the ScanGauge update speed?
Isn't there a way to do just one, I don't want everything since the instant MPG jumps too fast than.
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Old January 28th, 2008, 14:24   #12
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Quote:
Originally Posted by TheDieselFamily
Seftonm, your original post sounds like you did the XGage upgrade your self. Is this the case? If so can you share how you did it, or point those of us with the pre-XGage somehwere to help?

The ScanGage II web site says you have to send the unit back for the upgrade. I do not want to go without the ScanGage, especailly when I am pulling a trailer.

Thanks...
You can add it yourself if you have a more current verison (with xguage) if not you need to send it in and they will update it.
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Old January 28th, 2008, 16:37   #13
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Quote:
Originally Posted by MPLSTDI
You can add it yourself if you have a more current verison (with xguage) if not you need to send it in and they will update it.
That's right, my ScanGauge came with XGauge already installed. All I did was use the XGauge feature to create a boost gauge.

MPLSTDI, there is not a way that I know of to change the update speed of individual gauges. I will let you know if I find anything.
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Old January 28th, 2008, 17:17   #14
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Quote:
Originally Posted by seftonm
That's right, my ScanGauge came with XGauge already installed. All I did was use the XGauge feature to create a boost gauge.

MPLSTDI, there is not a way that I know of to change the update speed of individual gauges. I will let you know if I find anything.
Thanks
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Old January 29th, 2008, 13:52   #15
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hey seftonm- if you can figure out the coding for a fuel temperature xgauge lots of members would be grateful!
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