#### seftonm

##### Veteran Member

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--GrowResources.php?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

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

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--GrowResources.php?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

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