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Test L: No Module/Network Communications - ISO 9141 Network

NOTE: After making any repair, perform data link diagnostic procedure. See DATA LINK DIAGNOSTIC TEST  under SELF-DIAGNOSTIC SYSTEM.
NOTE: Depending on module configuration, with all modules connected and with ignition switch in RUN position or with engine running 2-3 volts may be present at Data Link Connector (DLC) terminal No. 7 (Light Blue/White wire). This is the International Standards Organization (ISO) 9141 diagnostic communications network circuit.
  1. Turn ignition switch to LOCK position. Inspect Data Link Connector (DLC) for connector for loose, damaged or corroded terminals. Pay particular attention to terminals No. 4 (Black wire) and No. 7 (Light Blue/White wire). See Figure. Repair as necessary. If connector is okay, go to next step.
  2. Disconnect Generic Electronic Module (GEM) Gray 26-pin connector C239. Inspect GEM connector C239 for loose, damaged or corroded terminals. Repair as necessary. If connector is okay, go to next step.
  3. Measure resistance of Light Blue/White wire between GEM connector C239 terminal No. 25 and DLC terminal No. 7. See Figure and Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in Light Blue/White wire between GEM connector C239 and DLC.
  4. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue/White wires). If both readings indicate zero volts, replace GEM. See GENERIC ELECTRONIC MODULE/CENTRAL TIMER MODULE (GEM/CTM) under REMOVAL & INSTALLATION in ANALOG INSTRUMENT PANELS - EXPEDITION, F150 & F250 LIGHT-DUTY PICKUPS, & NAVIGATOR article. If either reading indicates voltage and vehicle is not equipped with Driver's Seat Module (DSM) and air suspension control module, go to step  8. If either reading indicates voltage and vehicle is equipped with DSM and air suspension control module, go to next step. If either reading indicates voltage and vehicle is only equipped with DSM (no air suspension module), go to next step. If either reading indicates voltage and vehicle is only equipped with air suspension control module (no DSM), go to step  7.
  5. Turn ignition switch to LOCK position. Disconnect DSM 22-pin connector C356. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue/White wires). If either reading indicates voltage, go to next step. If both readings indicate zero volts, replace DSM. See DRIVER SEAT MODULE under REMOVAL & INSTALLATION in POWER SEATS - EXPEDITION, PICKUPS & NAVIGATOR article.
  6. Turn ignition switch to LOCK position. Disconnect in-line Black 66-pin connector C201. See Figure. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue wires). If either reading indicates voltage and vehicle is equipped with air suspension control module, go to next step. If either reading indicates voltage and vehicle is not equipped with air suspension control module, go to step  8. If both readings indicate zero volts, repair Light Blue/White wire between DSM connector and in-line connector C201 (female side).
  7. Turn ignition switch to LOCK position. Disconnect air suspension module 16-pin connector C296. Air suspension module has two 16-pin connectors. Connector C296 has blank terminal No. 13. See Figure. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue/White wires). If either reading indicates voltage, go to next step. If both readings indicate zero volts, replace air suspension module. See appropriate ELECTRONIC article in SUSPENSION.
  8. Turn ignition switch to LOCK position. Disconnect Remote Anti-Theft Personality (RAP) module Black 26-pin connector C256. See Figure. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both are Light Blue wires). If either reading indicates voltage, go to next step. If both readings indicate zero volts, replace RAP module. See REMOTE ANTI-THEFT PERSONALITY MODULE  under REMOVAL & INSTALLATION.
  9. Turn ignition switch to LOCK position. Disconnect in-line Gray 16-pin connector C247. See Figure. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue wires). If either reading indicates voltage, go to next step. If both readings indicate zero volts, repair Light Blue/white wire between in-line connector C247 (male side) and RAP module connector.
  10. Turn ignition switch to LOCK position. Disconnect 4-Wheel Anti-Lock Brake System (4WABS) module Black 24-pin connector. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue/White wires). If either reading indicates voltage, go to next step. If both readings indicate zero volts, replace 4WABS module.
  11. Turn ignition switch to LOCK position. Disconnect in-line Gray 40-pin connector C160. See Figure. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue/White wires). If either reading indicates voltage, go to next step. If both readings indicate zero volts, repair Light Blue/White wire between 4WABS connector and in-line connector C160 (male side).
  12. Turn ignition switch to LOCK position. Deactivate air bag system. See appropriate AIR BAG RESTRAINT SYSTEMS article. Disconnect Restraint Control Module (RCM) 26-pin connector. Connect GEM Gray 26-pin connector C239. Turn ignition switch to RUN position. Measure voltage between DLC terminals No. 7 (Light Blue/White wire) and No. 4 (Black wire). Measure voltage between DLC terminals No. 7 and 16 (both Light Blue/White wires). If either reading indicates voltage, repair Light Blue/White wire. If both readings indicate zero volts, replace RCM. See RESTRAINT CONTROL MODULE (RCM) under REMOVAL & INSTALLATION in AIR BAG RESTRAINT SYSTEMS - EXPEDITION, EXPLORER, MOUNTAINEER & NAVIGATOR article.
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