What causes lost communication with ECM/PCM Chevy?

If you're experiencing lost communication with the Engine Control Module Powertrain Control Module (ECMPCM) in your Chevy vehicle, there are several potential causes that can lead to this issue. This article will provide a detailed overview of the common reasons for lost ECMPCM communication and the steps you can take to diagnose and resolve the problem.

Causes of Lost ECMPCM Communication in Chevy Vehicles

The ECMPCM is a critical component in Chevy vehicles, responsible for managing the engine and powertrain systems. When communication between the vehicle's computer and the ECMPCM is lost, it can result in a range of issues, from poor engine performance to the illumination of the check engine light. Some of the most common causes of lost ECMPCM communication include:

• Wiring Harness Issues: Damaged, corroded, or loose wiring connections in the ECMPCM wiring harness can disrupt the communication between the vehicle's computer and the module. This can be caused by wear and tear, environmental factors, or improper installation.


• Faulty ECMPCM: The ECMPCM itself may be malfunctioning due to a hardware failure, software glitch, or other internal issues, leading to a loss of communication with the vehicle's computer.


• Electrical System Problems: Issues with the vehicle's electrical system, such as a failing battery, alternator, or ground connections, can also interfere with the ECMPCM's ability to communicate effectively.


• Diagnostic Tool Errors: In some cases, the loss of ECMPCM communication may be due to errors or compatibility issues with the diagnostic tool being used to interface with the vehicle's computer system.

It's important to note that the specific cause of the lost ECMPCM communication in your Chevy vehicle may vary depending on the model, year, and other factors. A thorough diagnosis by a qualified automotive technician is often necessary to identify the root cause and implement the appropriate solution.

Diagnosing and Resolving Lost ECMPCM Communication

If you're experiencing lost ECMPCM communication in your Chevy vehicle, here are the steps you can take to diagnose and resolve the issue:

1. Perform a Diagnostic Scan: Use a compatible diagnostic tool to scan the vehicle's computer system for any diagnostic trouble codes (DTCs) related to the ECMPCM. These codes can provide valuable clues about the underlying cause of the communication issue.


2. Inspect the Wiring Harness: Carefully examine the ECMPCM wiring harness for any signs of damage, corrosion, or loose connections. Repair or replace any faulty wiring components as needed.


3. Test the ECMPCM: If the wiring harness appears to be in good condition, the ECMPCM itself may be the source of the problem. Use a multimeter or other diagnostic tools to test the module's functionality and determine if it needs to be replaced.


4. Check the Electrical System: Ensure that the vehicle's battery, alternator, and ground connections are in good working order, as issues with the electrical system can also contribute to lost ECMPCM communication.


5. Update Diagnostic Software: If the issue persists, it's possible that the diagnostic tool being used is not compatible with the specific Chevy model or may have outdated software. Consider updating the diagnostic software or using a different tool to interface with the vehicle's computer system.

By following these steps and working with a qualified automotive technician, you can effectively diagnose and resolve the lost ECMPCM communication issue in your Chevy vehicle, restoring proper engine and powertrain performance.

How much does it cost to fix a U0100 code?

Fixing a U0100 code can cost anywhere from $50 to over $2,000, depending on the underlying issue, with the total price determined by the complexity of the repair. Simple fixes like replacing a fuse or a faulty battery can be inexpensive, while more complex problems like replacing and programming the Engine Control Module (ECM) can be very costly. 
Cost breakdown by repair type

• Basic repairs:
  • Wiring, fuse, or battery replacement: \$50–\$300. A weak battery is a very common cause of this code. 
• Intermediate repairs:
  • Software updates: \$100–\$300. 
  • Diagnostics: A professional diagnostic scan can cost around \$60–\$100. 
• Advanced repairs:
  • Module replacement (ECM/PCM): \$200–\$1,500, or even over \$2,000, depending on the vehicle. This is one of the most expensive potential fixes. 
  • ECM/PCM repair: Some specialized shops can repair a defective ECM, which may be cheaper than replacement. 

What to consider

• Diagnosis is key: The first step is to diagnose the problem. A mechanic will need to determine if the issue is a simple fix or a more expensive component failure. 
• Potential for high cost: Be prepared for higher costs if the ECM itself is faulty, as replacing and programming a new one can be expensive and time-consuming. 
• Safety: It is recommended to address a U0100 code immediately, as it can cause the engine to stall, enter "limp mode," or fail to start, which can be dangerous. 

Why are my ECM and PCM not communicating?

In some cases a shorted sensor can bring the communication to a halt. With these types of errors you can communicate with the module. But the information from the sensor is missing or implausible.

How do I fix code U0100?

To fix a U0100 code, start with basic checks like testing the battery and inspecting fuses and relays for the Engine Control Module (ECM) or Powertrain Control Module (PCM). Next, inspect the wiring harness and connectors for damage, corrosion, or loose connections. If the problem persists, the issue could be a faulty module, such as the ECM or PCM, which may require professional diagnosis. 
Basic checks

• Check the battery: A weak or failing battery can cause communication errors. Ensure it is fully charged and in good condition. Recharge or replace it if necessary. 
• Inspect fuses and relays: Locate the fuses and relays related to the ECM/PCM and check them for any blown or faulty parts. A simple continuity test with a multimeter can be used. 
• Check for other codes: Use a scan tool to check for other related trouble codes, which can provide clues about a deeper problem, such as a faulty Body Control Module (BCM) or a CAN bus issue. 

This video demonstrates how to inspect fuses and wiring for the ECM/PCM: 59sUpFix Automotive Electronics RepairYouTube · Feb 4, 2025
Advanced checks

• Inspect wiring and connectors: Carefully examine the wiring harness and connectors between the ECM and other modules for signs of damage, corrosion, or loose pins. Pay close attention to connectors that may have been disconnected during previous repairs. 
• Check the CAN bus: Inspect the Controller Area Network (CAN) bus wiring for shorts or open circuits, as this can cause communication failures. 
• Test for software updates: Check if there are any available software updates for your vehicle's ECM or TCM, as an outdated system can cause communication problems. 

When to seek professional help

• Module replacement: If all wiring, fuses, and connectors are in good condition, the ECM/PCM itself may be faulty and need replacement. This is typically a last resort after all other troubleshooting steps have been exhausted. 
• Professional diagnosis: If you are unsure how to proceed or if the problem is complex, it is best to have your vehicle diagnosed by a professional. They have the specialized tools and expertise to properly test the CAN bus system and other modules. 

This video explains how to diagnose the CAN bus communication line and what to check: 58sHVAC Mechanic YouTube · Aug 26, 2023

What does lost communication with ECM/PCM A mean?

"Lost communication with ECM/PCM A" means the vehicle's powertrain control module (PCM) or engine control module (ECM) cannot communicate with other control modules on the network, often causing performance issues or the vehicle to not start. This can be due to a problem with the vehicle's communication network (CAN bus), a blown fuse, a faulty wiring harness, or a weak battery. The "A" typically indicates a specific module or set of modules involved in the communication breakdown.
 
What the code means

• U0100 code: This is the generic diagnostic trouble code (DTC) for this issue, which signals a loss of communication between the ECM/PCM and another control unit. 
• ECM/PCM: The Engine Control Module (ECM) or Powertrain Control Module (PCM) is the central computer for the engine and transmission systems. 
• CAN bus: The ECM/PCM communicates with other modules (like ABS, airbag, or body control) using a network called the Controller Area Network (CAN bus). 

Common causes

• Power supply issues: A weak battery, bad battery connections, or a blown fuse related to the ECM/PCM can cause a loss of communication. 
• Wiring and connector problems: Damage to the wiring harness, a loose ground connection, or a corroded/dirty connector can interrupt the signal. 
• Faulty module: The ECM/PCM itself or another control module on the network could be malfunctioning. 
• CAN bus issue: A fault within the CAN bus network, such as a problem with a terminating resistor, can cause this error. 

Potential symptoms
Poor acceleration, Rough idling, Reduced fuel efficiency, Difficulty starting the engine, and The vehicle may enter "limp mode," which limits performance.