Rough Road Sensor: Description and Operation

G SENSOR
The powertrain control module (PCM)/engine control module (ECM) receives rough road information from the G sensor. The PCM/ECM uses the rough road information to enable or disable the misfire diagnostic. The misfire diagnostic can be greatly affected by crankshaft speed variations caused by driving on rough road surfaces. The G sensor generates rough road information by producing a signal which is proportional to the movement of a small metal bar inside the sensor.
If a fault occurs which causes the PCM/ECM to not receive rough road information between 30 and 80 mph (50 and 132kph), DTC P1391 will set.