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Condition Some customers may comment on intermittent illumination of the Service 4WD light. Upon investigation, the technician may find DTC C0374 set. The customer may also comment on intermittent erratic operation of the 4WD or AWD system after driving through rain/snow or simply going through a car wash. Cause The speed sensor signal may have become corrupted. Possible openings in the speed sensor wire insulation (twisted pairs) can allow water intrusion. Also, wire connections contaminated by water may result in short circuits and erroneous speed sensor readings. This most often occurs on the rear speed sensor circuit. Correction Inspect the wiring harness to the transfer case speed sensors. On Rainier, TrailBlazer, Envoy and 9-7X models, fabricate a replacement speed sensor harness between the C101 connector and the speed sensors. Completely inspect and test all wiring. Refer to Speed Signal, Front Axle Actuator, and Indicators schematic in SI. Replace the affected twisted pairs. Do not over-twist the two wires in the replacement harness. Wires should be twisted at a rate of 9 revolutions per foot. Use service connector pack, P/N 88987993, at the speed sensor end and terminal, P/N 15326267, at C101. Terminal testing tools and service terminals can be found in Terminal Repair Kit J 38125. Terminals are available from SPX/Kent-Moore. Call 1-800-GM-TOOLS (1-800-468-6657). The smaller transfer case harness splices into the larger chassis harness a few inches in front of the

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During cranking, the Ignition Control Module (ICM) monitors the 7X crankshaft position sensor signal. Once the ICM determines spark synchronization, 3X reference signals are sent to the PCM. The PCM will command all six injectors ON for one priming shot of fuel in all cylinders. After the priming, the injectors are left OFF for the next six fuel control reference signals (two crankshaft revolutions). This allow each cylinder a chance to use the fuel from the priming shot. During this waiting period, a cam pulse will have been received by the PCM. The PCM uses the Cam signal pulses to initiate sequential fuel injection. The PCM constantly monitors the number of pulses on the Cam signal circuit and compares the number of Cam pulses to the number of 24X reference pulses and the number of 3X reference pulses being received. If the PCM receives an incorrect number of pulses on the Cam reference circuit, DTC P0341 will set and the PCM will initiate injector sequence without the Cam signal with a one in six chance that injector sequence is correct. The engine will continue to start and run normally, although the misfire diagnostic will be affected if a misfiring condition occurs. Conditions for Running the DTC The engine is running (3X reference pulses are being received).

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SUBJECT: MODELS: Heated Windshield Washer Module Short Circuit – Add Wire Harness 2006-2008 model year Buick Lucerne; Cadillac DTS; HUMMER H2 vehicles; 2007- 2008 model year Cadillac Escalade, Escalade ESV, Escalade EXT; Chevrolet Avalanche, Silverado, Suburban, Tahoe; GMC Acadia, Sierra, Yukon, Yukon XL; Saturn OUTLOOK vehicles; and 2008 model year Buick Enclave vehicles equipped with a heated washer fluid system. A short circuit on the printed circuit board for the washer fluid heater may overheat the control-circuit ground wire. This may cause other electrical malfunctions, create an odor, or cause smoke. In rare cases, it may cause a fire. PARTS INFORMATION No parts are required to pull the heated windshield washer fuse. When wire harnesses are available for ordering, a revised bulletin with ordering information will be sent to dealers/retailers. SERVICE PROCEDURE Important: Until wire harnesses become available, the following procedure allows dealers/retailers to remove the heated windshield wiper fuse, disabling the system. 2007-2008 Cadillac Escalade, Escalade EXT, Escalade ESV, 2007-2008 Chevrolet Avalanche, Silverado (GMT900), Suburban, Tahoe, 2007-2008 GMC Sierra (GMT900), Yukon and Yukon XL 1. Disconnect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection in SI. Important: The underhood fuse block is located in the engine compartment on the driver side of the vehicle. Refer to Underhood Fuse Block in the Owner’s Manual for fuse information. 2. Locate the underhood bussed electrical center (UBEC). 3. Remove the UBEC cover and locate the 60 amp heated windshield washer fuse. Important: Remove the two relays (1) next to the fuse to gain access to the fuse. 4. Remove the 60 amp heated windshield washer fuse (2) using needle-nose pliers. 5. Store the 60 amp heated windshield washer fuse in the glove compartment. 6. Install the two relays (1) removed in Step 4. 7. Connect the negative battery cable. Refer to Battery Negative Cable Disconnection and Connection in SI. 8. Test the operation of the windshield wiper system. 8.1 Ensure the wiper system functions in low and high positions. 8.2 Verify that the windshield wiper/washer switch functions. The windshield wiper system should provide wiper fluid to the windshield. 8.3 Ensure that the heated windshield washer fluid system has been disabled. • Verify that the heated windshield washer switch does NOT flash. 9. Secure the UBEC cover on the UBEC. 10. Close the hood.

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Circuit Description The control module enables the appropriate fuel injector on the intake stroke for each cylinder. An ignition 1 voltage is supplied directly to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. Diagnostic Aids • Monitoring the fuel injector circuit status with a scan tool, while moving the fuel injector harness, may help to isolate an intermittent condition. • Performing the Fuel Injector Coil Test may help isolate an intermittent condition. Refer to Fuel Injector Solenoid Coil Test . • For an intermittent condition, refer to Intermittent Conditions . Test Description The numbers below refer to the step numbers on the diagnostic table. 4. This step tests for a short to ground on the ignition 1 voltage supply circuit of the fuel injector. 5. This step tests for an open ignition 1 voltage supply circuit between the injector fuse and a fuel injector electrical connector.

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Circuit Description The PCM monitors system voltage on the PCM ignition feed circuit. If the system voltage is out of tolerance, DTC P0560 will be set. When the conditions that set DTC P0560 are present, operation of some vehicle systems and components may be affected. Conditions for Setting the DTC • The engine is running. • System voltage monitored at the PCM ignition feed circuit is less than 9 volts or greater than 16 volts. • Above conditions for longer than 25 seconds. Action Taken When the DTC Sets • The PCM will not illuminate the malfunction indicator lamp (MIL). • The PCM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data. Conditions for Clearing the MIL/DTC • A History DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction. • The DTC can be cleared by using the scan tool Clear Info function.