Connecting to vehicle sensor.

I am planning on reading voltage from a vehicle's MAP sensor (Manifold Absolute Pressure) to make a vacuum gauge. Conveniently the sensor's output is 0-5v. I am planning on splicing into the output of this sensor and running it to an analog pin on the Andruino.

My concern is if there is a chance of feeding voltage back into the vehicle's wiring as this sensor goes to the engine computer and used to determine fuel regulation. Is this going to be a problem?

Is this going to be a problem?

No. Analog pins are read-only. There is no way to make one output a voltage.

My concern is if there is a chance of feeding voltage back into the vehicle's wiring as this sensor goes to the engine computer and used to determine fuel regulation. Is this going to be a problem?

I think the greater concern would be on whether the extra load on the sensor output would cause potential issues with the vehicle's computer (that is, by branching off, will the EMC think the output the sensor is different and adjust accordingly?). Then again, others have done it without any issues, so it probably isn't an issue. Likely, the 5V output of the sensor is of a sufficient current level that the branch to a microcontroller or similar device has little to no influence...