How to Read and Clear Transmission Fault Codes with Allison DOC

Introduction

Allison DOC (Diagnostic Optimized Connection) is the official diagnostic software developed by Allison Transmission for accurate communication with its Transmission Control Modules (TCMs). One of the most common and essential functions technicians use Allison DOC for is reading and clearing fault codes, also known as Diagnostic Trouble Codes (DTCs).

Fault codes are critical for identifying underlying issues in the transmission system—from electrical faults and sensor malfunctions to fluid pressure anomalies and shift failures. This guide will walk you through how to properly read, interpret, and clear transmission fault codes using Allison DOC, ensuring your troubleshooting process is efficient and correct.

What Are Transmission Fault Codes?

Transmission fault codes are diagnostic messages generated by the Transmission Control Module (TCM) when it detects irregularities in operation. These codes are stored within the module’s memory and may trigger a warning light or impact how the transmission behaves—often putting it into “limp mode” to prevent further damage.

Each DTC consists of:

• A fault code number (e.g., P0700, P0875)

• A description or system label

• Status (Active, Inactive, or Stored)

• A snapshot of the operating conditions when the fault occurred

Allison DOC not only reads these codes but also provides detailed manufacturer-specific explanations and repair procedures—something generic tools usually can’t do.

Preparing to Read Fault Codes in Allison DOC

Before starting, ensure you’ve completed the following:

1. Laptop Setup

   • Windows 10 or 11 installed

   • Latest version of Allison DOC software

   • RP1210-compatible adapter drivers (e.g., Nexiq, DPA5)

2. Vehicle Setup

   • Vehicle ignition turned ON (engine OFF)

   • Diagnostic adapter connected via USB or Bluetooth

   • Correct diagnostic port (usually 6- or 9-pin Deutsch) plugged in securely

3. Software Setup

   • Launch Allison DOC as Administrator

   • Select the appropriate communication device and protocol (J1939 or J1708)

   • Confirm successful connection to ECM (TCM info should populate automatically)

Once connected, you’re ready to retrieve fault codes.

How to Read Fault Codes with Allison DOC

Step 1: Navigate to the DTC Tab

After a successful connection, Allison DOC will load the vehicle profile and show several tabs. Click on the “DTCs” (Diagnostic Trouble Codes) tab to access fault codes.

Step 2: Review the Fault Code List

The software will display:

• A list of active and inactive fault codes

• A status indicator (Active, Previously Active, or None)

• A brief description of the fault

• System identifiers (e.g., Main Pressure, Shift Solenoid)

• A timestamp and snapshot of when the fault was triggered

Step 3: Access Fault Details

By clicking on any individual code, you can view:

• Detailed definition of the code

• Potential causes and components involved

• Recommended diagnostic flow

• System diagrams or circuit references (if applicable)

This information is pulled directly from Allison’s OEM database, giving you insights that generic scan tools cannot provide.

Understanding Active vs. Inactive Codes

Allison DOC classifies DTCs into:

• Active DTCs: Currently present and affecting transmission operation.

• Previously Active DTCs: Occurred in the past but are no longer present. Useful for understanding intermittent or self-corrected issues.

• None: No faults detected at the time of scan.

You should never clear fault codes without first reviewing active issues, performing diagnostics, and verifying that the problem has been resolved.

How to Clear Transmission Fault Codes in Allison DOC

Step 1: Address the Root Cause

Before clearing any fault codes:

• Run output tests to confirm component behavior

• Inspect wiring, sensors, and actuators

• Perform fluid checks or pressure tests

• Replace or repair faulty components

Clearing codes without solving the actual problem may temporarily reset the warning but can lead to repeat failures.

Step 2: Use the “Clear Codes” Function

1. Navigate to the DTC tab

2. Click the “Clear All DTCs” button

3. Confirm the action when prompted

4. Wait for the software to process the command

5. Allison DOC will show “No active faults” if all codes were successfully cleared

Some codes may not clear if the issue is still present or if the TCM requires a key cycle (ignition OFF then ON) before clearing.

What to Do If Codes Won’t Clear

If you attempt to clear DTCs but they reappear immediately or cannot be erased, consider the following:

• The fault condition is still physically present (e.g., failed sensor or solenoid)

• There is an intermittent fault triggering the code during startup

• A low voltage condition is preventing the ECM from resetting

• The software may require an elevated access level to clear manufacturer-protected codes

In such cases:

• Recheck the fault using live monitoring tools in Allison DOC

• Restart the ignition and try again

• Use OEM-level credentials if necessary

• Update TCM firmware if outdated (requires higher access)

Best Practices When Working with Fault Codes

• Always record DTCs and snapshots before clearing

• Use the Snapshot feature to capture operating conditions during fault events

• Keep a log of cleared codes, especially in fleet environments

• If unsure, refer to Allison service documentation or call tech support

• Never assume a cleared code means the problem is fixed—verify with test results

Conclusion

Reading and clearing transmission fault codes is a fundamental part of Allison DOC’s capabilities, but it’s not just about pressing a button. With proper understanding of how codes are generated, categorized, and interpreted, technicians can diagnose and repair transmission systems with precision.

By following this structured approach to DTC management using Allison DOC, you reduce the risk of repeated failures, improve service efficiency, and keep vehicles in reliable operation.