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Test 7: No Module/Network Communications - ISO 9141 Link

WARNING: This page is about a different car, the 2001 Mazda B4000, 2001 Mazda B3000, 2001 Mazda B2500, and 2001 Mazda B2300. However, it is still accessible from the selected car via links, so may be relevant.
NOTE: ISO 9141 communication network will not function if Light Blue/White wire is shorted to ground or power. Steps  3- 11 are used for locating a short.
  1. Turn ignition switch to OFF position. Inspect Data Link Connector (DLC) for physical damage, bent terminals or corrosion. Pay particular attention to terminal No. 7 (Light Blue/White wire). See Figure. Repair connector as necessary and retest system for normal operation. If connector is okay, go to next step.
  2. Turn ignition switch to OFF position. On 2.5L models, disconnect GEM 26-pin harness connector (T-221). On 3.0L and 4.0L models, disconnect GEM 20-pin harness connector (T-2100a). See Figure. Using DVOM, measure resistance in Light Blue/White wire between GEM terminal No. 25 (T-221) or No. 3 (T-2100a) and DLC terminal No. 7. See Figure or Figure . If resistance is less then 5 ohms go to next step. If resistance is more than 5 ohms, repair Light Blue/White wire between GEM and DLC. See WIRING DIAGRAMS . Retest system.
  3. Retest ISO network communications. See DATA LINK DIAGNOSTIC TEST  under SELF-DIAGNOSTIC SYSTEM. If system did not pass test, fault does not lie with GEM. Reconnect GEM connector, and go to next step. If system passed diagnostic test, check GEM connectors for damaged or corroded terminals. Repair connectors as necessary, then retest system with GEM connected. If GEM connectors are okay, or fault persists, replace GEM. Retest system.
  4. If vehicle is not equipped with 4WD, go to step  6. If vehicle is equipped with 4-Wheel Drive (4WD), disconnect 4WD control module connector (H281). See Figure. Measure resistance of Light Blue/White wire between 4WD control module connector (H281) terminal No. 4 and DLC terminal No. 7. See Figure. If resistance is less then 5 ohms, go to next step. If resistance is more than 5 ohms, repair Light Blue/White wire between 4WD control module and DLC. See WIRING DIAGRAMS . Retest system.
  5. Retest ISO network communications. See DATA LINK DIAGNOSTIC TEST  under SELF-DIAGNOSTIC SYSTEM. If system did not pass test, fault does not lie with 4WD control module. Reconnect 4WD control module connector (H281), and go to next step. If system passed diagnostic test, check 4WD control module connectors (H281) for damaged or corroded terminals. Repair connectors as necessary, then retest system with 4WD control module connected. If 4WD control module connectors (H281) are okay, or fault persists, replace 4WD control module. Retest system.
  6. If vehicle is not equipped with a Central Security Module (CSM), go to step  10. If vehicle is equipped with CSM, disconnect CSM 26-pin connector (T-410). Measure resistance of Light Blue/White wire between CSM connector terminal No. 3 and DLC terminal No. 7. See Figure. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair Light Blue/White wire between CSM and DLC. See WIRING DIAGRAMS .
  7. Retest ISO network communications. See EQUIPMENT HOOKUP  under SELF-DIAGNOSTIC SYSTEM. If system did not pass test, fault does not lie with CSM. Reconnect CSM connector (T-410), and go to next step. If system passed diagnostic test, check CSM connector (T-410) for damaged or corroded terminals. Repair connectors as necessary, then retest system with CSM connected. If fault persists, replace CSM. Retest system.
  8. If vehicle is not equipped with 4 Wheel Anti-Lock Braking System (4WABS), go to step  10. If vehicle is equipped with 4WABS, disconnect 4WABS 25-pin harness connector. See Figure. Measure resistance of Light Blue/White wire between 4WABS 25-pin harness connector terminal No. 23 and DLC terminal No. 7. If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, repair Light Blue/White wire between 4WABS module and DLC. See WIRING DIAGRAMS . Retest system.
  9. Retest ISO network communications. See DATA LINK DIAGNOSTIC TEST  under SELF-DIAGNOSTIC SYSTEM. If system did not pass test, fault does not lie with 4WABS control module. Reconnect 4WABS control module connector, and go to next step. If system passed diagnostic test, check 4WABS control module connector for damaged or corroded terminals. Repair connectors as necessary, then retest system with 4WABS control module connected. If fault persists, replace 4WABS control module. Retest system.
  10. Deactivate air bag system. See AIRBAG RESTRAINT SYSTEM - PICKUP article. Disconnect air bag diagnostic monitor harness connector located under beverage tray. Measure resistance of Light Blue/White wire between air bag diagnostic module terminal No. 5 and DLC terminal No. 7. See Figure. If resistance is less then 5 ohms, go to next step. If resistance is more than 5 ohms, repair Light Blue/White wire between air bag diagnostic monitor harness and DLC. Retest system.
  11. Retest ISO network communications. See DATA LINK DIAGNOSTIC TEST  under SELF-DIAGNOSTIC SYSTEM. If system did not pass self-test, fault does not lie with air bag diagnostic monitor. Reconnect air bag diagnostic monitor connector, and then retest. Problem may have been caused by a loose or corroded connector. If system passed diagnostic test, check air bag diagnostic monitor connector for damaged or corroded terminals. Repair connectors as necessary, then retest system with air bag diagnostic monitor connected. If fault persists, replace air bag diagnostic monitor. Retest system.
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