Barometrc pressure switch???

[tift104]

Ok I am curious what the purpose of a Barometric pressure switch is? Reason for asking is this. Our M108S is used in forestry applications. It has a custom cage and push blade on the front. After transporting the tractor about a 100 miles away for a pine tree mowing job the light came on as soon as I unloaded off the semi. I immediately shut it down, checked all fluids (which were ok) then started calling our Kubota dealer back home. They told me that that light means that a something has triggered a sensor that it was possible that it was low brake fluid or the water in the radiator was a little low to check those things. They told me that the machine could still be used just to bring it in when it gets back. So I ran it like it was. There was no noticeable lag in power and it ran flawlessly through out the entire job. When we finally slowed down I took it to my Kubota dealer. After sitting for almost a week they finally hooked up to their computer and it threw a code for the alternator. Now I called myself testing the alternator with my meter tester. It showed 12volts when turned off and 12.9 volts when running. I never had to jump or charge the battery the entire 7 months it ran after the light came on. (Keep in mind this is a cab tractor with AC & Heat). The dealer replaced the alternator and the light was still on. They hooked it to the computer again and it threw another code. This time they said it was a Barometric Pressure sensor. They told me that this sensor is inside the ECU and the only fix was to replace the entire ECU to the tune of 2500.00 plus labor. But they did say that I would still be able to use the tractor like it is the light just would not go off.
I'm jut looking for a second opinion. The light I'm describing is a small red circle with a exclamation point in the middle (!). Its is not the big circle in the middle of the dash that usually is followed by an annoying beeping noise.
Thanks in advance for your thoughts.

 

[PILOON]

Works OK?
Cut the wire or tape over that light.

LOL, I had a GMC 'Jimmy' that had an annoying warning light that would not go away,
Since dash was black I simply covered it over with black electricians tape.(my OB2 reader gave no clues and dealer wanted a ransom to hook it up to a computer)
Drove it 2 years with tape and traded it in on a Kia Sorrento and still got a reasonable trade value.

 

[s219]

Well, if it were a modern car, the atmospheric pressure sensor would be used to fine tune the fuel/air schedule (also known as fuel/air map). Not sure what function it has in a diesel tractor, but if it's advanced enough to have an ECU it may be doing the same thing. I suppose in the worst case, you might see slightly worse performance or higher fuel consumption at extremes in barometric pressure. Really depends on how sensitive the tune is to atmospheric pressure.

 

[PILOON]

At higher elevations the oxygen is rarer so for ultimate power mixture needs to be adjusted.
A chainsaw tuned at sea level will need carb adjusting at elevations as low as 2000 ft.
In my 20's we drove a VW beetle in Mexico and at 6000 ft it could barely drive in 1st gear due to lack of O2 so we changed the carb air jet and were good to go.

Probably all related to CARB regs and will simply burn somewhat richer at elevation creating a bit more soot in the exhaust. Back to sea level and you'll burn off that soot. Maybe change oil a bit more often as it would get darker faster due to added soot from extended altitude usage.

 

[Chilly807]

The M108 is turbocharged, I think? If it has an electronically controlled injection system, then the pressure switch monitors intake manifold pressure and sends that information to the ECU to limit fuel delivery based on pressure. The Tier 4 emission tractors probably have that sensor as well, whether they're turbocharged or not.