Owning a Duramax diesel truck means enjoying the benefits of power and reliability. However, even the best machines can face issues. Seeing a P0700 code pop up on your dashboard can be worrisome, as it hints at potential problems within your transmission control system. Understanding why your Duramax is setting this code will help you repair the problem in a timely manner.

What Is a P0700 Code?

The transmission control module (TCM) oversees the transmission’s performance, ensuring smooth gear shifts and optimal operation. In Duramax diesel trucks, this code signals that the TCM has detected a problem within the transmission but it does not tell the whole story. P0700 is a generic/non-specific code which is triggered when the TCM detects an issue and will notify the ECM (Engine Control Module). When the P0700 is found, you will need to scan the TCM directly with a GM Tech II scanner or something similar. Scanning the TCM will give you the Transmission direct error codes for further diagnosis. 

Diagnosing the Problem

Addressing a P0700 code requires a systematic approach:

• Scan for Additional Codes stored in the TCM

  • Use an GM Tech-II or similar scanner to identify additional codes stored in the TCM. These codes can provide more specific information about the underlying issue. Once you have the codes from the TCM pulled, please follow the GM recommended diagnoses and resolutions based on the code provided.

Common Causes of a P0700 Code

Several factors can trigger a P0700 code in your Duramax truck:

• Faulty Transmission Control Module

  • A malfunctioning TCM can lead to improper communication between your vehicle’s systems. A disruption can prompt the check engine light and result in a P0700 code.

• Wiring Issues

  • Damaged, frayed, or corroded wiring can interrupt signals between the TCM and other components. Inspect the wiring for visible damage, and secure all connections.

• Transmission Fluid Problems

  • Low, high, dirty, or contaminated transmission fluid can affect the transmission’s performance. Regularly check and replace the fluid as needed to avoid issues. If you tow often, we recommend servicing the transmission every 25-35K. If the truck is used lightly in daily driven applications you may stretch this to 50k depending on the fluid condition. Here is a great video walking you through a standard Allison 1000 Service:

• Sensor Malfunctions

  • Various sensors monitor the transmission’s operations. A faulty sensor can send incorrect data to the TCM and trigger the P0700 code.

• Internal Transmission Issues

  • Worst case scenario, there may be issues within the transmission that can include clutch slippages, converter failures, or valvebody/solenoid issues. 

Solutions and Repairs

Fixes to the P0700 code is going to be based solely on the codes pulled from the TCM and the GM recommended diagnoses/R&R of the symptoms you are seeing. We do have a huge selection of replacement parts including full rebuilds if necessary. 

Conclusion

A P0700 code in your Duramax diesel truck signifies a problem within the transmission. By understanding the potential causes and taking a diagnostic approach, you can resolve the issue and enjoy smooth and reliable drives once again.