Rough Road Sensor: Description and Operation

DESCRIPTION AND OPERATION
The Gravity (G) sensor is a vertical low-g (gravity) acceleration sensor. By sensing vertical acceleration caused by bumps or potholes in the road, the powertrain control module (PCM) can determine if the changes in crankshaft speed are due to engine misfire or are driveline induced. If the G sensor detects a rough road condition, the PCM misfire detection diagnostic will be de-activated. The G sensor at rest output is very close to 2.5 volts (+1G). During a G sensor condition, the voltage output can vary between 0.5 volt (-1G) and 4.5 volts (+3G). 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 to not receive rough road information between 50 km/h and 132 km/h (30 mph and 80 mph), DTC P1391 will set.