DTC U2105: Lost Communication With ECM
- Perform VEHICLE ON-BOARD DIAGNOSTIC SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM. If vehicle on-board diagnostic system check has been performed, go to next step.
- Using scan tool, attempt to establish communication with ECM. If scan tool is not able to communicate with ECM, go to next step. If scan tool is able to communicate with ECM, go to step 6.
- Check BCM/ECM/CRUISE/ABS fuse (10-amp) and CONTROLS B+ fuse (10-amp), located in underhood fuse block. See COMPONENT LOCATIONS . If fuses are okay, go to next step. If fuse(s) is blown, replace appropriate fuse(s) and check affected circuit(s) for short to ground. See POWER DISTRIBUTION article in WIRING DIAGRAMS. Repair affected circuit as necessary and retest operation.
- Turn ignition off. Access ECM. See COMPONENT LOCATIONS . Disconnect Black 64-pin ECM connector. Turn ignition on. Connect test light between ground and ECM connector J2 terminals No. 15 (Orange wire), and No. 47 (Pink wire). See Fig 1. If test light illuminates on both circuits, go to next step. If test light does not illuminate on either circuit, repair open in Orange wire between ECM and CONTROLS B+ fuse (10-amp), or open in Pink wire between ECM and BCM/ECM/CRUISE/ABS fuse (10-amp). See POWER DISTRIBUTION article in WIRING DIAGRAMS. Retest operation.
- Connect test light between battery voltage and ECM case. If test light does not illuminate, repair ground to ECM case and retest operation. If test light illuminates, check for poor connections to ECM. Repair as necessary. If ECM connections are okay, replace ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE.
- If BCM DTCs U2105 and U2106 are set, go to step 8. If BCM DTCs U2105 and U2106 are not set, go to next step.
- Turn ignition off for 10 seconds. Turn ignition on. Using scan tool, observe scan tool display for DTC U2105 in BCM and TCM. If scan tool displays LAST TEST FAILED for DTC U2105 for BCM and TCM, ECM is unable to communicate on CAN link. Replace ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE. If scan tool does not display LAST TEST FAILED for DTC U2105 for BCM and TCM, problem is intermittent. Check all connections and CAN link circuits for an open. See DATA LINK CONNECTORS article in WIRING DIAGRAMS.
- Turn ignition off for 10 seconds. Turn ignition on. Using scan tool, observe scan tool display for DTC U2105 and U2106 in BCM. If scan tool displays LAST TEST FAILED for DTC U2105 and U2106 for BCM, go to next step. If scan tool does not display LAST TEST FAILED for DTC U2105 and U2106 for BCM, problem is intermittent. Check all connections and CAN link circuits for an open. See DATA LINK CONNECTORS article in WIRING DIAGRAMS.
- Turn ignition off. Access BCM. See COMPONENT LOCATIONS . Turn ignition on. Using a DVOM, back probe and measure voltage between Pink 24-pin BCM connector J3 terminal A12 (Tan wire) and terminal B11 (Tan/White wire), and ground. If voltage is 1.5-3.5 volts on both circuits, go to next step. If voltage is not 1.5-3.5 volts on both circuits, check CAN low or CAN high circuits for short to ground or voltage. Perform short to ground or voltage diagnosis in DTC U2100: CAN BUS COMMUNICATIONS MALFUNCTION test.
- Turn ignition off. Disconnect Pink 24-pin BCM connector J3. Turn ignition on. Using a DVOM, measure voltage between ground and BCM harness connector J3 terminal A12 (Tan wire) and terminal B11 (Tan/White wire). If voltage is not 1.5-3.5 volts, go to next step. If voltage is 1.5-3.5 volts on both circuits, check all connections between BCM and ECM. If all connections are okay, replace BCM. See BODY CONTROL MODULE under REMOVAL & INSTALLATION.
- Check for open in Tan wire (CAN low circuit) or Tan/White wire (CAN high circuit), or for loose connections between BCM and ECM. If circuits and connections are okay, replace ECM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article in ENGINE PERFORMANCE.
Courtesy of GENERAL MOTORS CORP.