Update tpms_nissan.c

[CppBaddy]

Fixed reported pressure_psi value.

[zuckschwerdt]

Thanks!
The inversion of the documented (PSI+THREE)*FOUR would be float pressure_psi = (float)pressure_raw / 4.0f - 3.0f;, won't it?

[CppBaddy]

I found by accident that the pressure value tracks my tire gauge better. Original formula gives much lower values. To verify, I am going to capture some data from my winter wheels tonight.
BTW: do you remember the source of original formula? From what I see in schrader_SMD3MA4_decode raw value just gets divided by 5. This decoder gets my original Nissan sensors. The tpms_nissan reads aftermarket sensors I use in winter tires.

[zuckschwerdt]

The decoder was merged from #2536 but I messed up the pressure by applying the factor twice.

I think only that error should be corrected. The difference in measurement you see is more likely due to operating temperature?

[zuckschwerdt]

See #2157 (reply in thread) which I might have missed back then.

the TPMS sensor uses "sealed gauge" (internal absolute pressure reference) it may or may not read the same as your tire pressure gauge, depending on your elevation.

It should be corrected to use just / 4 with no offset.

[CppBaddy]

Ok, this makes sense, I'll make changes then.

[zuckschwerdt]

Thanks! Sorry to be picky, could you use 4.0f to be consistent with other float literals?

[CppBaddy]

No worries, fixed.
Cheers!