U0755 - Communication Circuit for the Transmission Control Module (TCM) Malfunction in GM Vehicles

Quick Answer

U0755 means: U0755 indicates a communication failure between the ECM and TCM, affecting vehicle transmission performance.

Fix: Check and replace faulty components Cost: $150 - $400 Time: 90-180 minutes

Can I drive with U0755? Immediate attention is required to prevent further damage to the transmission.

Common Questions

What does U0755 mean and how does it affect my car?

The U0755 code indicates a communication failure between the Engine Control Module (ECM) and the Transmission Control Module (TCM). This can lead to poor shifting performance and may cause the transmission to behave erratically, resulting in a loss of power or responsiveness. Ignoring this code can escalate into major transmission issues, so it’s crucial to address it promptly.

What are the most common causes of U0755 and how much does it cost to fix?

Common causes of the U0755 code include faulty wiring (50% likelihood), a malfunctioning TCM (30%), and poor battery voltage. Repair costs can vary widely, ranging from $150 for wiring repairs to $1,500 for a TCM replacement, depending on the exact issue and labor involved.

Can I drive my car with U0755 or should I stop immediately?

It is not advisable to drive your vehicle if the U0755 code is present. Doing so can exacerbate the issue, potentially leading to further damage to the transmission. It's best to have the vehicle diagnosed and repaired as soon as possible.

How can I diagnose U0755 myself using GeekOBD APP?

To diagnose U0755 with the GeekOBD APP, connect the device to your OBD2 port, run a full scan to retrieve codes and freeze frame data, and check for any additional codes related to transmission issues. You can also monitor live data to assess the performance of the ECM and TCM.

What vehicles are most commonly affected by U0755?

The U0755 code is frequently reported in General Motors vehicles, particularly the Chevrolet Silverado and GMC Sierra from 2007 to 2019, as well as Cadillac models like the SRX and CTS. Regular maintenance and software updates can help mitigate risks.

How can I prevent U0755 from happening again?

Regular vehicle maintenance is key to preventing U0755. This includes checking for loose or corroded connections, ensuring that the battery is in good condition, and keeping the TCM dry and free from moisture. Additionally, using quality parts during repairs can help maintain the integrity of your vehicle's electrical system.

What is U0755?

The diagnostic trouble code (DTC) U0755 indicates a communication error between the vehicle's Engine Control Module (ECM) and the Transmission Control Module (TCM). This code is particularly common in General Motors vehicles, including models like the Chevrolet Silverado (2007-2019) and GMC Sierra (2007-2019). When the ECM and TCM fail to communicate effectively, it can lead to serious performance issues, as the transmission relies on commands from the ECM for proper shifting and overall operation. This malfunction can manifest in various ways, including erratic shifting, poor acceleration, or even the vehicle going into 'limp mode' to protect the engine and transmission from damage. Car owners may notice that the check engine light illuminates, and they may experience symptoms like delayed shifting or a jerky feel when changing gears. Understanding the implications of this code is essential because failing to address the underlying communication issue can lead to more significant repairs down the line, including transmission replacement. Therefore, it's crucial to diagnose and remedy the problem as soon as possible to maintain the vehicle's performance and safety.

System: U - Network (Communication, CAN Bus)

Symptoms

Common symptoms when U0755 is present:

  • The check engine light stays on constantly, indicating a persistent issue that needs addressing.
  • The vehicle may experience delayed or harsh shifting, making it uncomfortable to drive, especially in stop-and-go traffic.
  • Engine performance issues may arise, such as hesitation during acceleration or a lack of power, affecting overall drivability.
  • Fuel economy may decrease significantly, with some drivers reporting a drop of 10-15%, leading to increased operating costs.
  • In severe cases, the vehicle may enter a 'limp mode', restricting speed and acceleration to prevent further damage.

Possible Causes

Most common causes of U0755 (ordered by frequency):

  1. The most common cause of U0755 is a faulty wiring harness or connector, which accounts for about 50% of cases. Damaged wires can disrupt communication between the ECM and TCM.
  2. A malfunctioning Transmission Control Module itself can also trigger this code, with a likelihood of around 30%. This can happen due to internal failures or software issues.
  3. Poor battery voltage or a failing alternator can lead to communication problems, so maintaining battery health is crucial. Regular checks can help prevent this issue.
  4. Less common but serious causes include water intrusion in the TCM, which can short circuit the module and disrupt communication. Ensuring proper sealing can prevent this.
  5. Rarely, issues with the Engine Control Module can also cause the U0755 code, leading to a more complicated diagnosis and repair process.

U0755 Repair Costs

Cost Breakdown by Repair Type

Wiring Harness Repair

Repairing or replacing damaged wiring or connectors that affect ECM and TCM communication.

  • Total: $150 - $400
  • Success rate: 85%
TCM Replacement

Replacing a malfunctioning Transmission Control Module with a new or refurbished unit.

  • Total: $800 - $1,500
  • Success rate: 90%
Money-Saving Tips for U0755
  • Start with the most common and least expensive repairs first
  • Use GeekOBD APP to confirm diagnosis before replacing expensive parts
  • Consider preventive maintenance to avoid future occurrences
  • Compare prices for OEM vs aftermarket parts based on your needs
  • Address the issue promptly to prevent more expensive secondary damage

Diagnostic Steps

Professional U0755 Diagnosis Process

Follow these systematic steps to accurately diagnose U0755. Each step builds on the previous one to ensure accurate diagnosis.

Step 1: Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around connectors (5-10 minutes)

Step 1: Initial visual inspection - Check for obvious signs like damaged wiring, loose connections, or corrosion around connectors (5-10 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 2: Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context and history of the vehicle (10-15 minutes)

Step 2: OBD2 scan with GeekOBD APP - Retrieve all codes and freeze frame data to understand the fault context and history of the vehicle (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 3: Step 3: Component testing - Use a multimeter or specific diagnostic tools to test the resistance and voltage levels of suspected components (20-30 minutes)

Step 3: Component testing - Use a multimeter or specific diagnostic tools to test the resistance and voltage levels of suspected components (20-30 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 4: Step 4: System function test - Verify proper operation after repairs are made, and clear the codes to see if they return (10-15 minutes)

Step 4: System function test - Verify proper operation after repairs are made, and clear the codes to see if they return (10-15 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.
Step 5: Step 5: Road test verification - Drive the vehicle under various conditions to confirm that the problem is resolved and no new codes appear (15-20 minutes)

Step 5: Road test verification - Drive the vehicle under various conditions to confirm that the problem is resolved and no new codes appear (15-20 minutes).

GeekOBD APP Tip: Use GeekOBD APP to monitor real-time data during this diagnostic step for accurate results and professional-grade analysis.

Important Notes

  • Always verify the repair with GeekOBD APP after completing diagnostic steps
  • Clear codes and test drive to ensure the problem is resolved
  • Address underlying causes to prevent code recurrence

Real Repair Case Studies

Case Study 1: Resolving U0755 in a 2015 Chevrolet Silverado

Vehicle: 2015 Chevrolet Silverado 1500, 50,000 miles

Problem: Customer reported the check engine light was on, along with rough shifting and decreased power.

Diagnosis: Initial OBD2 scan revealed U0755. A visual inspection found damaged wiring in the harness connecting the ECM and TCM.

Solution: Repaired the wiring and secured all connections. Cleared the codes and performed a road test.

Cost: $250 (including parts and labor)

Result: The check engine light remained off, and the transmission shifted smoothly during the road test.

Case Study 2: TCM Replacement for U0755 in a 2018 GMC Sierra

Vehicle: 2018 GMC Sierra 1500, 30,000 miles

Problem: Customer experienced delayed shifting and the check engine light was illuminated.

Diagnosis: Diagnostic scan confirmed U0755. Further testing indicated a malfunctioning TCM that failed to communicate with the ECM.

Solution: Replaced the Transmission Control Module and updated the vehicle’s software.

Cost: $1,100 (including TCM and labor)

Result: Post-repair, the vehicle showed no further issues and shifting was restored to normal.

Diagnose U0755

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Code Information

Code: U0755
System: Network (Communication, CAN Bus)
Severity: HIGH
Category: Network Codes