The following statements regarding the exhaust gas recirculation (egr) valve are all correct except: low restriction exhaust systems will have no effect on egr system operation. b. some systems monitor egr operation using a manifold absolute pressure (map) sensor. c. a potentiometer is used to determine egr valve position. d. the powertrain control module (pcm) controls vacuum-operated egr valves.

B. Some systems monitor EGR operation using a manifold absolute pressure (MAP) sensor.

Explanation:

The Manifold Absolute Pressure (MAP) sensor is a device used to measure absolute pressure inside the engine, it is used to calculate gas quantity needed to be injected into the cylinder and also for engine load input by the powertrain control module (PCM).

It is not used with the EGR as a monitor.

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true