Description & Operation

WARNING: This page is about a different car, the 2002 Mercury Grand Marquis and 2002 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

Vehicle has 2 module communications networks. Standard Corporate Protocol (SCP) communication network, which is an unshielded twisted pair cable (data bus plus, and data bus minus) and International Standards Organization (ISO) 9141 communications network which is a single-wire network (Circuit 70). Both networks can be connected to diagnostic tool by one connector called Data Link Connector (DLC). This makes diagnosis and testing of these systems easier by allowing one smart tester to be able to diagnose and control any module on two networks from one connector. DLC can be found under instrument panel between steering column and radio. ISO 9141 communication network does not permit intermodule communications. When diagnostic tool communicates to modules on ISO 9141 communication network, diagnostic tool must ask for all information; modules cannot initiate communications. SCP communication network will remain operational even with severing of one of the bus wires. Communications will also continue if one of the bus wires is shorted to ground or battery positive voltage (B+), or if some but not all termination resistors are lost. Unlike SCP communication network, ISO 9141 communication network will not function if wire is shorted to ground or battery positive voltage (B+). Also, if one of the modules on ISO 9141 communication network loses power or shorts internally, communications to that module will fail.

Electronic Crash Sensor (ECS) is connected to ISO 9141 communication network. ECS controls deployment of air bags based on sensor input. Driver Door Module (DDM) is connected to SCP communication network. Module controls many functions including power windows, power locks and keyless remote entry. Lighting Control Module (LCM) is connected to SCP communication network. LCM controls both interior and exterior lighting, anti-theft functions and warning chimes. Electronic Automatic Temperature Control (EATC) module is connected to SCP communication network. EATC module controls automatic climate functions that maintain vehicle at a constant temperature setting. Powertrain Control Module (PCM) is connected to SCP communication network. PCM controls engine performance, electronic ignition, emission controls and on-board diagnostics. Natural Gas Vehicle Module (NGVM) calculates fuel level based on inputs from fuel tank pressure sensor and fuel tank temperature sensor. NGVM then provides a voltage signal to instrument cluster to drive fuel gauge. NGVM also has separate injector drivers to run injectors at higher operating pressure of natural gas. NGVM does not perform any calculations for this function; calibration for injectors is maintained in PCM. Anti-lock brake control module is connected to SCP communication network. Module controls brake pressure to four wheels to keep vehicle under control while braking. Passive Anti-Theft System (PATS) module is on SCP communication network. PATS module communicates with PCM to disable and start vehicle based on a signal received from an encoded ignition key signal.

Some vehicles are equipped with Electric Variable Assist (EVO) power steering. If vehicle is equipped with EVO, steering is controlled by EVO steering module. If vehicle is equipped with EVO and rear air suspension, air suspension/EVO steering module controls rear suspension and power steering. Air suspension/EVO steering module and EVO steering module do not use network communications.