Principles of Operation

WARNING: This page is about a different car, the 2004 Mercury Marauder, 2004 Mercury Grand Marquis, and 2004 Ford Crown Victoria. However, it is still accessible from the selected car via links, so may be relevant.

The diagnostic tool connects to the two networks through the 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 the two networks from one connector. The DLC can be found under the instrument panel between the steering column and the radio.

The ISO 9141 communications network does not permit intermodule communication. When the diagnostic tool communicates to modules on the ISO 9141 communication network, the diagnostic tool must request all information; or initiate module commands.

The ISO 9141 communications network will not function if the wire is shorted to ground or battery voltage. Also, if one of the modules on the ISO 9141 communications network loses power or shorts internally, communications to that module will fail.

The SCP communications network will remain operational even with the severing of one of the bus wires. Communications will also continue if one of the bus wires is shorted to ground or voltage, or if some but not all termination resistors are lost.

The restraint control module (RCM) is connected to the ISO 9141 communication network. The ECS controls the deployment of the air bags based on sensor input. For additional information, refer to AIR BAG RESTRAINT SYSTEMS .

The driver door module (DDM) is connected to the ISO 9141 communication network. The module controls many functions including power windows, power locks and keyless remote entry. For additional information, refer to HANDLES, LOCKS, LATCHES AND ENTRY SYSTEMS .

The lighting control module (LCM) is connected to the ISO 9141 communication network. The LCM controls both interior and exterior lighting, anti-theft functions and warning chimes. For additional information on interior lighting, refer to INTERIOR LIGHTING . For additional information on exterior lighting, refer to EXTERIOR LIGHTING . For additional information on anti-theft, refer to ANTI-THEFT . For additional information on warning chimes, refer to WARNING DEVICES .

The electronic automatic temperature control (EATC) module is connected to the SCP communication network. The EATC module controls automatic climate functions that maintain the vehicle at a constant temperature setting. For additional information, refer to CLIMATE CONTROL SYSTEM-GENERAL INFORMATION .

The powertrain control module (PCM) is connected to the SCP communication network. The PCM controls the engine performance, electronic ignition, emission controls and on-board diagnostics. For additional information, refer to ELECTRONIC ENGINE CONTROLS . The passive anti-theft system (PATS) is integrated into the PCM. The PCM controls the PATS functions as well as illumination of the anti-theft indicator. The illumination command is sent from the PCM through the SCP communications network to the instrument cluster, which in turn sends power to the anti-theft indicator. The PCM stores the ignition key codes and controls engine disable. For additional PATS information, refer to ANTI-THEFT .

The natural gas vehicle module (NGVM) calculates fuel level based on inputs from the fuel tank pressure sensor and the fuel tank temperature sensor. The NGVM then provides a voltage signal to the instrument cluster to drive the fuel gauge. The NGVM also has separate injector drivers to run the injectors at the higher operating pressure of natural gas. The NGVM does not perform any calculations for this function; calibration for the injectors is maintained in the powertrain control module (PCM). For additional information, refer to INSTRUMENT CLUSTER-NATURAL GAS VEHICLE .

The anti-lock brake control module is connected to the SCP communication network. Vehicles not equipped with traction control use the ISO network. The module controls the brake pressure to the four wheels to keep the vehicle under control while braking. For additional information, refer to ANTI-LOCK CONTROL-TRACTION CONTROL & STABILITY ASSIST .

The rear air suspension module (RASM) is connected to the SCP communication network. The RASM controls the rear ride height. Refer to VEHICLE DYNAMIC .