Grand Cherokee 2WD V8-4.7L VIN J (2004)
The ACM also contains an energy-storage capacitor. When the ignition switch is in the Start or On positions, this capacitor is continually being
charged with enough electrical energy to deploy the airbags for up to one second following a battery disconnect or failure. The purpose of the
capacitor is to provide backup supplemental restraint system protection in case there is a loss of battery current supply to the ACM during an impact.
Two sensors are contained within the ACM, an electronic impact sensor and a safing sensor. The ACM also monitors inputs from two remote front
impact sensors located on brackets on the inboard sides of the right and left vertical members of the radiator support near the front of the vehicle. The
electronic impact sensors are accelerometers that sense the rate of vehicle deceleration, which provide verification of the direction and severity of an
impact. On models equipped with optional side curtain airbags, the ACM also monitors inputs from two remote side impact sensors located near the
base of both the left and right inner B-pillars to control the deployment of the side curtain airbag units.
The safing sensor is an electronic accelerometer sensor within the ACM that provides an additional logic input to the ACM microprocessor. The
safing sensor is used to verify the need for a supplemental restraint deployment by detecting impact energy of a lesser magnitude than that of the
primary electronic impact sensors, and must exceed a safing threshold in order for the airbags to deploy. Vehicles with the optional side curtain
airbags feature a second safing sensor within the ACM to provide confirmation to the ACM of side impact forces. This second safing sensor is a
bi-directional unit that detects impact forces from either side of the vehicle.
Pre-programmed decision algorithms in the ACM microprocessor determine when the deceleration rate as signaled by the impact sensors and the
safing sensors indicate an impact that is severe enough to require supplemental restraint system protection and, based upon the severity of the
monitored impact, determines the level of front airbag deployment force required for each front seating position. When the programmed conditions are
met, the ACM sends the proper electrical signals to deploy the dual multistage front airbags at the programmed force levels and, if the vehicle is so
equipped, either side curtain airbag.
The hard wired inputs and outputs for the ACM may be diagnosed and tested using conventional diagnostic tools and procedures. However,
conventional diagnostic methods will not prove conclusive in the diagnosis of the ACM, the PCI data bus network, or the electronic message inputs to
and outputs from the ACM. The most reliable, efficient, and accurate means to diagnose the ACM, the PCI data bus network, and the electronic
message inputs to and outputs from the ACM requires the use of a DRBIII scan tool. Refer to the appropriate diagnostic information.
