Bosch 4BAR MAP sensor 0281006102

[mituc]

For those who self-tune and you have this sensor, this is the calibration you need to use:
Multiplier: 90
Offset: -5

So in Versatuner you can set the Base Multiplier to 90, Second Multiplier to 1 and Offset to -5.

I've seen a lot of calibrations flying around from various tuners (which I'd expect to know better, but for some reason they do not care) and they were all wrong by a lot (based on min/max MAP values assuming they were always at 0.5 and 4.5V, which is not always the case).

[mituc]

I've seen some people questioning this. Which is fine. Here is how it works:
1. the Bosch specs say that the sensor will read 50kPa at 0.5V and 400kPa at 4.5V;
2. the response curve on these sensors is actually a straight line defined by the two above points;
3. probing the sensor we found that at baro it outputs 1.08V, and that baro at the time of measurement (with precise tools + other readings from other sensors) was 102.2kPa.

So for 1 and 2, we have:
0.5*M - O = 50
4.5*M - O = 400
-> O = 0.5*M - 50
-> 4.5*M - 0.5*M + 50 = 400
-> 4*M = 350
-> M = 87.5
-> O = -6.25

So with this multiplier and offset at 1.08V we have: 87.5*1.08 - ( -6.25) = 100.75kpa instead of 102.3 which is about 1.5% off.
If we re-do the equations above but using the 1.08V reference instead of the 4.5:
0.5*M - O = 50
1.08*M - O = 102.2

-> 1.08*M-0.5M + 50 = 102.2
-> 0.58M = 52.2 -> M = 90, O = -5.
Ok, what will this give us at 4.5V:
4.5*90 - (-5) = 410, which is a 2.5% deviation at the end, which is better as an error margin than having 1.5% at basically 18% from the total voltage interval from the specs. And now we also know the sensor reads baro properly which is a very good reference.

Another possible option could be to manipulate the offset and have a constant deviation of like 1.5kPa across the entire range (multiplied 87.5 and offset of -7.5) instead of having the whole response curve (line) pivoted slightly up from the same base (50kPa at 0.5V).
Either would work but in such situations we should measure the sensor response on a bench having another very precise gauge as a reference in at least one more voltage point further away from what we know it reads at baro (say, at like 2V or even higher).
So 90 and -5 are easy to remember (as would be 87.5 / -7.5 though) and exact at the baro reference we have.