Diagnostic guide for U0073

Diagnostic Guide for U0073 - Control Module Communication Bus OFF

The U0073 code indicates a communication issue within the vehicle's control modules, specifically related to the General Motor Local Area Network (GMLAN). The goal of this diagnostic guide is to identify the root cause of the communication failure and restore proper functionality.

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Difficulty

Intermediate

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Estimated Time

30-60 Minutes

Estimated Diagnostic Cost

$0-$100

Typical shop charge to perform this diagnostic process. Repair parts and labor are not included.

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Tools Needed

OBDII scanner, multimeter, wiring diagram, basic hand tools

Safety Notes

Ensure the vehicle is in a safe position, with the engine off and keys removed. Be cautious of moving parts and hot surfaces during inspection.

Step 1

Scan for Codes

Instruction Connect the OBDII scanner to the vehicle's diagnostic port and read all stored trouble codes.

Expected result A list of trouble codes, including U0073 and any related codes.

If Pass If U0073 is present along with other codes, note them for further diagnosis.

If Fail If no codes are present, the issue may be intermittent or related to a power supply problem. Check the vehicle's battery and fuses.

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Step 2

Inspect Wiring and Connectors

Instruction Visually inspect the wiring harness and connectors for the modules involved in the GMLAN for any signs of damage, corrosion, or loose connections.

Expected result Wiring and connectors should be intact and securely connected.

If Pass If everything appears normal, proceed to test the modules for communication.

If Fail Repair or replace any damaged wiring or connectors found during the inspection.

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Step 3

Test Module Communication

Instruction Using the OBDII scanner, attempt to communicate with each module on the GMLAN to determine if they respond correctly.

Expected result Modules should respond to commands without errors.

If Pass If all modules communicate, the issue may be intermittent or related to a specific module.

If Fail Identify which module(s) failed to communicate and note them for further testing.

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Step 4

Check Power and Ground to Modules

Instruction Using a multimeter, check for proper voltage and ground at the connectors of the non-communicating module(s).

Expected result Power and ground should be present as specified in the wiring diagram.

If Pass If power and ground are good, the module may be faulty and require replacement.

If Fail If power or ground is missing, trace the circuit back to find the fault, such as a blown fuse or broken wire.

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Step 5

Perform a Network Test

Instruction If a specific module is suspected, perform a network test to check for data transmission on the GMLAN.

Expected result Data should be transmitted correctly between modules.

If Pass If data transmission is normal, consider replacing the suspected faulty module.

If Fail If data transmission fails, further investigate the wiring or other modules on the network.

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Coddy can help with this step only. Tell me what you tested or what result you got.