Here are a list of temp calibration files for different cars, files here are made for units with aref = 256 (standard since early 2006, see BuildProcedures/SectionThree)
Most installs best work with tempsensor_upload.bat 2252 2252 256
that is
- 2252 Ohm ntc type sensor for airtempsensor and
- 2252 Ohm ntc type sensor for coolant as well
Let's say
- your NTC (standard coolant, airtemp) sensor measures 4780 Ohm at +10C
- the 2252 Ohm sensor is 4481.5 Ohm at +10C (see diagram or table below)
- from this, calculate your sensor nominal resistance (at +25C) as 4780 / 4481.5 * 2252 = 2402 that is closest to pre-generated calibration curve of 2400 Ohm
Plotted with gnuplot using logarithmic Y-scale:
You can also interpolate using data below (for almighty precision):\n
Celsius Ohm -50 150394 -40 75780 -30 39860 -20 21860 -10 12460 0 7352.8 10 4481.5 20 2812.8 25 2252 30 1814.4 40 1199.6 50 811.4 60 560.3 70 394.55 80 282.63 90 206.13 100 152.75 110 114.92 120 87.671 130 67.770 140 52.983 150 41.881
If you have doubts, provide measurement(s) so we can help you select the best temperature curve. Actually with the common ntc type sensor, just one temperature point is sufficient (easiest with cold engine when sensor temperature is same as environment)
- sensor temperature
- sensor Ohm (when disconnected from ECM)
- sensor voltage (when connected to ECM, ECM powered up)
- LCD reading at that temp
- TerminalProgram Manmlp00mll command
- mostly useful if the firmware's vems.hex is known (or at least first 50 lines of vems.hex)
Coolant Sensors
| Car Make | Car model | Engine | sensor partno# | Pullup R | calibration file link |
| Bosch (Volvo, BMW, VAG, etc...) | ... | ... | unknown | standard 2k7 | See Bosch below |
Air Temp Sensors
| Car Make | Car model | Engine | sensor partno# | Pullup R | calibration file link |
| Bosch (Volvo, BMW, VAG, etc...) | ... | ... | unknown | standard 2k7 | See Bosch below |
| Audi | many 5cyl | AAN/ABY/ADU/3B/etc... | PTC type, appr 500 Ohm at roomtemp | 429..430 Ohm | [PTC_airdenfactor_430_Ohm_pullup.txt]. For dead-on calibration, you can choose from [airXfactor_PTC_series.zip], Marcell found PTC_aref264_420 to be best for his Audi PTC. Note that the second number is higher for higher PTC value (or lower pullup) |
BOSCH sensors
For the classic 2057 Ohm (@T=+25C) NTC type sensor (often closer to 2063 Ohm in practice though difference is negligable), [NTC_PTC_clt_air.zip] 2063/263 (or 256 or 268) is best match.
- you can finetune the aref=256 or 263 or 268 at low temp (-20 .. +20C). 263 should be a close-enough starting point, but if you care to give it a final hair-split: 256 will read 3F lower, 268 will read 2F higher.
- if you don't know your sensor's resistance at T=+25C (which is often 2057..2063 or 2252 Ohm, but sometimes near 2900 Ohm), you can finetune the 2252 (change to lower or higher) at high temp (near +100C).
- Instead of the risks and hassle of boiling water for the sensor, to simulate +100C (for verification of the setup), you can use a constant resistor with value R=152.75 / 2252 * R25 = 0.068 * R25 (where R25 is the sensor resistance at +25C).
Most classical BOSCH NTC curve used from early 80s up to nowdays. No matter it is Volvo, Audi, Mercedes, Volksvagen, BMW etc - all of them had or have similar sensors.
Source: http://www.bosch-motorsport.de/pdf/sensors/temperature/NTC_M12.pdf
Both ...2063_256.hex and ...2252_256.hex give some degries mismatch at environment or engine operating temperatures. At tuning it is not heavy importance, but if LCD is used this is very welcome to see believable values on it.
Same isue had Miska Peippo described here: http://www.vems.hu/wiki/index.php?page=MembersPage%2FMiskaPeippo%2FAudiSSix