Today I was cleaning the interior or my car, and since I had my battery disconnected for some time, so I was curious to get to the ECM and open it to see the STA508A chip see the condition. Well the damnedest thing I didn't expect to find what was sitting on top of the ECM box, I see a Map Sensor. Why would Nissan put a MAP sensor inside the car, normally it would been on the intake or under hood. Has anyone seen it on their cars? It's odd place, I never thought ours wouldn't have one, but behind the dash sitting on top the ECM?!

 

There shouldn't be anything on top of the ECM (ECU). But I wonder if it really is a MAP sensor because I'm pretty sure those need a vacuum line. Can you post a photo?

 

Yeah I was wondering about that too.
Its an absolute pressure sensor.

 

I agree but not all MAP sensor have vaccum line attached it it. But here the photo since you can clearly see it's sit atop of the ECM. I thought why would it have it there, I owned this car since I bought it brand spanking new.

 

According to the FSM it measures barometric pressure? I would assume this is according to sea level?
Its probably used for the pressure sensors.

 

This is cut & paste from the 2003 FSM:

The absolute pressure sensor is built into ECM. The sensor detects
ambient barometric pressure and sends the voltage signal to the
microcomputer.

P0107 An excessively low voltage from the sensor is sent to ECM.
P0108 An excessively high voltage from the sensor is sent to ECM.

 

Used for emissions evap BS, isn't it?

 

What about mounting it just before the TB and just after the MAF?
Would this improve fuel mileage?

 

Just delete the word evap from that statement.

Feeding barometric info to the ECU should be part of the calculations for how much fuel to inject. Higher altitudes (less oxygen) need less fuel to avoid running rich and/or flooding out.

Locating the sensor by the throttle body might cause false readings because of the much hotter and therefore thinner air. That's a guess. The 4th gen Maximas had the MAP/BARO sensor at the air intake scoop on the radiator frame to get cooler air.