DESCRIPTION & OPERATION
Module communications network provides the ability for module-to-module communication by sharing inputs and outputs instead of each component having an input and output wired directly to each module. Vehicle has two module communications networks. First communications network is Standard Corporate Protocol (SCP) that is also referred to as data bus positive (circuit No. 914) and data bus negative (circuit No. 915), which consists of a pair of unshielded twisted wires. Second communications network is International Standards Organization (ISO) 9141, which consists of a single wire (circuit No. 70).
Worldwide Diagnostic System (WDS) tester, New Generation Star (NGS) tester or equivalent diagnostic tool can connect to both networks through the Data Link Connector (DLC). DLC is located under instrument panel between steering column and radio. (Scheme 1) 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. ISO 9141 communication network does not permit inter-module communication. When diagnostic tool communicates to modules on ISO 9141 communication network, diagnostic tool must ask for all the information, modules cannot initiate communications. SCP 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 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 the wire is shorted to chassis ground or battery positive voltage (B+). Also, if one of the modules on ISO 9141 network loses power or shorts internally, communications to that module will fail. Powertrain Control Module (PCM) is on SCP communication network. PCM controls engine for better fuel economy, emissions control, and failure mode detection and storage. Restraint Control Module (RCM) is on ISO 9141 network. RCM controls deployment of the air bags based on sensor input. Generic Electronic Module (GEM) is on ISO 9141 network. GEM module controls a variety of systems including one touch down windows, wipers, perimeter anti-theft, and warning chimes. Anti-Lock Brake System (ABS) control module communicates over ISO 9141 communication network when not equipped with traction control and communicates over SCP communication network when it is equipped with the traction control option. ABS control module controls brake pressure to the four wheels to keep vehicle under control while braking. Remote Climate Control (RCC) module is on the SCP communication network. The RCC module controls the temperature within the vehicle. For module locations. (Scheme 2) See COMPONENTS LOCATION table.
Scheme 1
Scheme 2
Principals of Operation
Some modules must be programmed as part of the repair procedure. If correct procedure is not followed, module may not function correctly and may set a number of Diagnostic Trouble Codes (DTC). Modules that require programming should not be exchanged between vehicles. In most cases, a vehicle's parameter values or settings are unique to that vehicle. Connect Worldwide Diagnostic System (WDS) tester, New Generation Star (NGS) tester or equivalent diagnostic tool to Data Link Connector (DLC). DLC is located under instrument panel between steering column and radio. (Scheme 1) Diagnostic tool tester will automatically attempt to retrieve module configuration information from all modules and from a back-up location in the PCM when Vehicle Identification (VID) is carried out. If module and PCM do not contain correct information, diagnostic tool tester will either request "As Built" data or display a list of items that you will need to manually configure them. Diagnostic tool tester will program module based on data entered. There are three different methods that are used for module programming
- Programmable Module Installation (PMI).
- Calibration up-date.
- Programmable parameters.
Some modules do not support all three methods. See MODULE PROGRAMMING.
Vehicle Identification Block Description
Some Powertrain Control Modules (PCM) contain a memory area called a Vehicle Identification (VID) block. VID block is used to store backup data for each programmable module, as well as, PCM configuration information. WDS, NGS or equivalent diagnostic tool tester cannot retrieve module option content information from suspect module, diagnostic tool tester will attempt to extract backup information from PCM's VID block. PCM VID block contains factory settings for configured modules unless PCM is flashed with a new calibration, in which case some PCM parameters may be modified.
As-Built Data Center Description
As-Built Data Center maintains a record of vehicle configuration in a database. Vehicle Identification Number (VIN) is required to obtain this information. As-Built Data Center records applicable module configurations stored in each module before vehicle leaves factory. As-Built Data Center will always reflect the original build of vehicle as it left the factory. Only contact As-Built Data Center when directed to do so by diagnostic tool.
ACCESSING PARAMETER IDENTIFICATION
Turn ignition switch to LOCK position. Connect Worldwide Diagnostic System (WDS) tester, New Generation Star (NGS) tester or equivalent diagnostic tool to Data Link Connector (DLC). DLC is located under instrument panel between steering column and radio. (Scheme 1) Following scan tool manufacturer's instructions, enter PID/DATA MONITOR AND RECORD for desired module. Operate appropriate system and ensure Parameter Identification (PID) expected values are obtained.
See also:
• SELF-DIAGNOSTICS - EEC-V - GASOLINE & NGV