2000 Cadillac CateraFACTORY OEM SERVICE PROCEDURE

DTC U2105: Lost Communication With Engine Control Module (ECM): Testing

  1. Perform appropriate diagnostic system check. See appropriate ENGINE PERFORMANCE article for ECM, appropriate AUTOMATIC TRANSMISSION article for TCM and appropriate ANTI-LOCK BRAKE/TRACTION CONTROL article for EBTCM. After performing diagnostic system check, go to next step.
  2. If DTC U2100 is recorded as a current or history code in ECM, EBTCM or TCM, go to U2100: CAN-BUS COMMUNICATION MALFUNCTION  . If DTC U2100 is not recorded as a current or history code in ECM, EBTCM or TCM, go to next step.
  3. Test following ECM circuits: Battery positive voltage circuit, ignition positive voltage circuit and ground circuit. Check operation of ECM power relay. See appropriate ENGINE PERFORMANCE article in ENGINE PERFORMANCE. If fault is located and repaired, go to step  8 . If fault is not located and repaired, go to next step.
  4. Disconnect electrical harness connector from module that set DTC U2105. Inspect harness connector for poor terminal contact, corrosion and damage. See PRELIMINARY INSPECTION  under TROUBLE SHOOTING. If fault is located and repaired, go to step  8 . If fault is not located and repaired, go to next step.
  5. Test CAN bus circuit between module that set DTC U2105 and ECM for an open. See WIRING DIAGRAMS  . If fault is located and repaired, go to step  8 . If fault is not located and repaired, go to next step.
  6. Disconnect electrical harness connector C2 from ECM. Inspect CAN bus circuit at harness connector for poor terminal contact, corrosion and damage. See PRELIMINARY INSPECTION  under TROUBLE SHOOTING. If fault is located and repaired, go to step  8 . If fault is not located and repaired, go to next step.
  7. Replace ECM. See REMOVAL & INSTALLATION  . After replacement, go to step  10 .
  8. Turn ignition off. Install scan tool to DLC. Turn ignition on. Using scan tool, select display DTCs for ECM. If scan tool displays any DTCs other than U2103, U2104, U2106 or U2108, go to BODY CONTROL MODULE (BCM) DTC DEFINITIONS  table and perform diagnostic test for that DTC. If scan tool does not display any DTCs other than U2103, U2104, U2106 or U2108, go to next step.
  9. Using scan tool, clear DTCs. See CLEARING DTCS  under SELF-DIAGNOSTIC SYSTEM. After clearing DTCs, go to next step.
  10. Using scan tool, select display DTCs for module that set DTC U2105. If scan tool displays any DTCs other than U2103, U2104 or U2105, perform diagnostic system check for automatic transmission and ABS system. See appropriate AUTOMATIC TRANSMISSION article for TCM and appropriate ANTI-LOCK BRAKE/TRACTION CONTROL article for EBTCM. If scan tool does not display any DTCs other than U2103, U2104 or U2105, go to next step.
  11. Using scan tool, clear DTCs. See CLEARING DTCS  under SELF-DIAGNOSTIC SYSTEM. Continue diagnosing and clearing DTCs until all modules have been diagnosed and all DTCs have been cleared. After repair, check system operation.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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