Several communication network problems have been identified, particularly in 01-05 trucks. These typically present as no crank or no start conditions, inaccurate Instrument Panel Cluster (IPC) readings such as fuel level and speed, unexpected door lock activations, and communication error codes between modules. On LB7 and LLY Duramax engines, these issues often arise from an outdated or weak communication system within the engine controllers. Symptoms include difficulties in reading or flashing the controller and engine start failures. A malfunctioning Fuel Injection Control Module (FICM) is frequently responsible.

This is often caused by corruption or a short in the Class 2 serial data network, and is usually caused by the interface module used with aftermarket radios; meanwhile, one must keep in mind that other aftermarket electronic accessories can also cause similar issues, and it isn't always the radio that will be the source of these issues. These issues are more commonly seen with radios equipped with GPS.

The diagnosis for this issue can be as easy as removing the radio fuse from the underhood fuse box and observing if the symptoms of the concern persist. Oftentimes these issues begin when batteries get weak and voltages drop below a certain threshold while cranking. Many customers will also experience these symptoms after replacing batteries. We have been oftentimes successful in correcting these issues by removing the radio fuse as previously mentioned, and starting the vehicle, allowing it to run for a few minutes and then while the vehicle is running, reintegrate the radio back into the network by reinstalling the fuse.

Symptoms:

• An LB7 or LLY that cranks but wont start or throws U0105 codes (No Communication with FICM).  
• Erratic behavior of the Instrument Panel Cluster (IPC), including incorrect fuel level, speed, or other readings.
• Communication codes between different modules (e.g., ECM, TCM, BCM).
• Transmission problems, such as a truck stuck in a particular gear (e.g., 2nd or 3rd), hard shifts, or going into "limp mode".
• Failed attempts to flash the ECM or TCM.

Troubleshooting steps

• Inspect fuses related to the communication network and relevant modules.
• Ensure the battery is fully charged and all ground connections are clean and secure.
• Inspect wiring harnesses and connectors for any visible damage or corrosion.
• Isolate the source:
• Temporarily remove fuses for aftermarket accessories like radios to see if the problem resolves.
• Consider swapping a known good module if you suspect a specific component failure (e.g., TCM, ECM, FICM).

Use a diagnostic tool:

• Utilize a scanner to check for diagnostic trouble codes and identify which modules are not communicating.
• If using flashing software, consider reverting to stock tunes or trying a different flashing method (e.g., low-speed flashing) if issues arise during programming.

Professional assistance:

• If basic troubleshooting doesn't yield results, consult a qualified mechanic or dealership, especially for complex electrical diagnoses or potential module replacement and programming.
• Communication problems can be tricky to diagnose, requiring systematic troubleshooting.

Communication issues in 01-05 trucks often cause no start, incorrect dashboard readings, and unexpected door lock activity. On LB7 and LLY Duramax engines, these problems usually stem from weak engine controller communication, frequently linked to a faulty Fuel Injection Control Module (FICM) caused by interference in the Class 2 serial data network. Aftermarket electronics, especially GPS-equipped radios, are common sources. Diagnosing is straightforward: removing the radio fuse can reveal if symptoms improve. These issues often arise when batteries weaken or are replaced. Restarting the vehicle without the radio fuse, then reinstalling it while running, can restore proper communication.