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HOMESERVICE MANUALSCHEVROLET2003TRAILBLAZER 4.2 S, 4WDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 945 (DATA LINK COMMUNICATION SYSTEM)DIAGNOSTIC INFORMATION AND PROCEDURESDTC U2104: CONTROLLER AREA NETWORK (CAN) BUS RESET COUNTER OVERRUNCONDITIONS FOR CLEARING THE MIL/DTC
2003 Chevrolet TrailBlazer 4.2 S, 4WD

Conditions for Clearing the MIL/DTC

2003 Chevrolet TrailBlazer 4.2 S, 4WDSECTION Conditions for Clearing the MIL/DTC
WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

The MIL/DTC clearing depends on DTC type. For information about DTC type refer to Diagnostic Trouble Code (DTC) Type(s) in Engine Controls - 6.6L (LB7).

DTC Type B

  • The MIL clears after 3 ignition cycles when the malfunction is no longer present.
  • A current DTC clears when the malfunction is no longer present.
  • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.

DTC Type C

  • A current DTC clears when the malfunction is no longer present.
  • A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction.
DTC U2104

Step Action Yes No
Schematic Reference: Data Link Connector (DLC) Schematics 
Connector End View Reference: Master Electrical Component List in Wiring Systems
1
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Does the DTC fail this ignition?		 Go to Step 2  Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
2
  1. Turn OFF the ignition.
  2. Disconnect the fuel injector control module (FICM).
  3. Disconnect the CAN circuits from the FICM.
  4. Reconnect the FICM.
  5. Operate the vehicle within the Conditions for Running the DTC.
  6. Retrieve DTCs from engine control module (ECM) and transmission control module (TCM).
Does the DTC reset as current in any module?		 Go to Step 3  Go to Step 5 
3
IMPORTANT:
  • If the vehicle is not equipped with TCM skip to the next step.
  • If the code set only in TCM, disconnect the ECM in this step.
  • If the code was set by ECM or by both modules, disconnect the TCM in this step.
  1. Turn OFF the ignition.
  2. Disconnect the module conform to the important statement.
  3. Disconnect the CAN circuits from the module.
  4. Reconnect the module.
  5. Operate the vehicle within the Conditions for Running the DTC.
  6. Retrieve DTCs from the module still connected.
Does the DTC reset as current?		 Go to Step 4  Go to Step 5 
4
IMPORTANT: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use DMM MIN/MAX function to capture intermittent conditions.
  1. Turn OFF the ignition.
  2. Disconnect the last module still connected to CAN bus.
  3. Test the CAN serial data circuits for a short to ground, short to voltage, an open, or a short between them. Refer to the following in Wiring Systems:
Did you find and correct the condition?		 Go to Step 7  Go to Step 5 
5 Inspect for an intermittent or poor connections at the last disconnected/reconnected module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
Did you find and correct the condition?		 Go to Step 7  Go to Step 6 
6
IMPORTANT: Perform the module setup procedure if required.
Replace the last disconnected/reconnected module. Refer to Control Module References in Body Control System.Did you complete the replacement?		 Go to Step 7  -
7
  1. Reconnect all wires and modules.
  2. Clear the DTCs with a scan tool.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine.
  5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 Go to Step 2  System OK.
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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.