Allison Transmission is one of the biggest companies that makes automatic gear for buses, trucks, and military vehicles. Allison Transmissions have a diagnostic system that can give trouble codes to show if there are problems with the transmission or other parts that go with it.
Please keep in mind that the fault codes for an Allison Transmission can be different based on the model of transmission and the type of vehicle. Also, Allison may sometimes update the software for its transmissions, which could change the list of trouble codes.
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Allison transmission fault code list
| Code | Description | Check Transmission Light |
|---|---|---|
| P01 | Input Speed Sensor No Signal | On |
| P02 | Output Speed Sensor No Signal | On |
| P03 | Engine Speed Sensor No Signal | Off |
| P04 | Vehicle Speed Sensor No Signal | Off |
| P05 | Transmission Control Module (TCM) Power Supply Low | On |
| P06 | TCM Internal Error | On |
| P07 | Torque Converter Clutch Solenoid Circuit No Signal | On |
| P08 | Reverse Solenoid Circuit No Signal | On |
| P09 | 4th/5th/6th Gear Solenoid Circuit No Signal | On |
| P10 | Line Pressure Solenoid Circuit No Signal | On |
| P11 | Brake Switch Signal Incorrect | On |
| P12 | Manual Valve Solenoid Circuit No Signal | On |
| P13 | Neutral Safety Switch Signal Incorrect | On |
| P14 | Adaptive Learning Not Available | Off |
| P15 | Input Speed Sensor Signal Erratic | On |
| P16 | Output Speed Sensor Signal Erratic | On |
| P17 | Engine Speed Sensor Signal Erratic | Off |
| P18 | Vehicle Speed Sensor Signal Erratic | Off |
| P19 | TCM Power Supply High | Off |
| P20 | TCM Power Supply Low | On |
| P21 | Torque Converter Clutch Solenoid Circuit Shorted | On |
| P22 | Reverse Solenoid Circuit Shorted | On |
| P23 | 4th/5th/6th Gear Solenoid Circuit Shorted | On |
| P24 | Line Pressure Solenoid Circuit Shorted | On |
| P25 | Brake Switch Signal Open | Off |
| P26 | Manual Valve Solenoid Circuit Shorted | On |
| P27 | Neutral Safety Switch Signal Open | Off |
| P28 | Adaptive Learning Not Enabled | Off |
| P29 | Input Speed Sensor Signal Intermittent | On |
| P30 | Output Speed Sensor Signal Intermittent | On |
| P31 | Engine Speed Sensor Signal Intermittent | Off |
| P32 | Vehicle Speed Sensor Signal Intermittent | Off |
| P33 | TCM Power Supply Intermittent | Off |
| P34 | Torque Converter Clutch Solenoid Circuit Overheated | On |
| P35 | Reverse Solenoid Circuit Overheated | On |
| P36 | 4th/5th/6th Gear Solenoid Circuit Overheated | On |
| P37 | Line Pressure Solenoid Circuit Overheated | On |
| P38 | Brake Switch Signal Intermittent | Off |
| P39 | Manual Valve Solenoid Circuit Overheated | On |
| P40 | Neutral Safety Switch Signal Intermittent | Off |
If you see any of these codes on your Allison transmission, it is important to have it checked by a qualified mechanic. The code may indicate a problem with the transmission that could lead to further damage if it is not repaired.