Allison Transmission Fault Codes
Allison Transmission builds fully automatic transmissions used behind virtually every major diesel engine -- Duramax, Cummins, Detroit Diesel, PACCAR, and CAT. Allison transmissions have their own Transmission Control Module (TCM) that reports faults using standard OBD-II P-codes in light-duty applications and J1939 SPN/FMI pairs in medium- and heavy-duty applications.
13 curated Allison TCM codes · 4 product series · TCM P-codes + J1939 · Light-duty to vocational HD
Allison Product Series
| Series | Typical Applications | Notes |
|---|---|---|
| 1000 Series | Chevrolet Silverado HD / GMC Sierra HD (Duramax), older medium-duty | Light-duty 6-speed automatic. Most commonly paired with the Duramax 6.6L in GM HD pickups. |
| 2000 Series | Medium-duty trucks, buses, RVs | Medium-duty applications. 5-speed or 6-speed automatic, often behind ISB 6.7L or ISL. |
| 3000 Series | Medium/heavy-duty trucks, fire apparatus, transit buses | Heavy commercial applications. 6-speed automatic rated up to ~60,000 lb GVW. |
| 4000 Series | Heavy-duty vocational: dump, refuse, concrete, oilfield | Heaviest-duty Allison automatic. Often paired with Cummins ISX/X15, DD16, or CAT in vocational trucks. |
Common Allison Fault Codes
Allison TCM codes appear as standard P07xx and P08xx OBD-II DTCs in the Allison 1000 series behind the Duramax. Heavier Allison installations (2000, 3000, 4000 series) report faults over J1939 and expose both proprietary Allison DTCs and SAE J1939 SPN/FMI pairs. Each code below links to the full diagnostic page with causes, tests, and fixes.
P0700
Transmission Control System malfunction -- generic TCM request for MIL illumination.
P0218
Transmission fluid over-temperature -- often Allison TES 295/668 fluid degradation or low fluid.
P0741
Torque Converter Clutch stuck off -- companion to P0742, often the same valve body cause.
P0742
Torque Converter Clutch stuck on -- common Allison 1000 failure behind Duramax.
P0776
Pressure Control Solenoid B stuck off -- often the PCS located inside the valve body.
P0871
Shift Solenoid E pressure switch -- solenoid pack or internal wiring harness.
P0872
Shift Solenoid E pressure switch circuit low -- related P0871 / valve body issue.
P0877
Shift Solenoid F pressure switch circuit -- common Allison 1000 valve body code.
P0731
Gear 1 incorrect ratio -- worn clutches or solenoid not engaging 1st properly.
P0732
Gear 2 incorrect ratio -- companion to P0731, often the same root cause.
P0733
Gear 3 incorrect ratio -- typically valve body or clutch pack wear.
P0734
Gear 4 incorrect ratio -- shift solenoid or clutch pack failure.
P0735
Gear 5 incorrect ratio -- common with valve body solenoid wear on high-mileage Allisons.
Most Common Allison Issues
- Valve body solenoid wear causing harsh shifts and P08xx codes in the Allison 1000
- Torque converter clutch (TCC) shudder and stuck-on codes (P0742) behind Duramax
- Fluid contamination -- Allison TES 295 / TES 668 specification is not optional on heavy series
- C3 pressure switch / PCS sensor issues on 3000/4000 series transmissions
- Limp mode (fifth-gear hold or neutral) triggered by range verification faults