Updated: 2026-11-10
The database covers 163 dealer codes — Allison uses its own factory format, outside the J1939 SPN/FMI standard. A few examples below; look up your own code in the search on the homepage, where you can also pick “Allison” from the brand list.
Allison is an automatic gearbox, and its codes are almost all about the transmission: 163 codes. The most common areas are transmission, lubrication and the CAN bus. The format is mixed: numbers such as 11 and 12, and codes such as P0121 and C1312. Before you search, establish which unit the code came from: the gearbox, the engine and the instruments can log similar faults under different numbers.
| C1312 | Retarder engage request — signal voltage low. Retarder disabled. |
| P0610 | Vehicle options hardware error. Calibration data from the TCM ID module (TID) is used. |
| P0703 | Brake switch signal problem. On refuse trucks, N-D range shifting is blocked; if the code is active, retarder operation is disabled. |
| P0717 | No turbine speed sensor signal. Diagnostics run, transmission locked in current gear. |
| P0733 | Incorrect gear ratio in 3rd gear. Diagnostics run, transmission tries 4th, then 6th. |
| P0776 | Fault in the PCS2 solenoid hydraulic circuit. Diagnostics run, limp-home (RPR) active. |
| P0847 | Pressure sensor PS2 — signal voltage low. |
| P0962 | Pressure control solenoid circuit — voltage low. Diagnostics run, solenoids off, hydraulic control active. |
| P0975 | Solenoid SS2 — open circuit. On the 7-speed transmission, 1-7 and reverse-1 shifts are disabled. |
| P1714 | Transmission pressure switch reverse circuit stuck on Check Trans light on. |
| P1779 | Engine torque delivered to ECM Check Trans light on. |
| P2670 | Circuit HSD2 — voltage low. Diagnostics run, solenoids off, hydraulic control active. |
| P2724 | Fault in the PCS1 solenoid hydraulic circuit. Diagnostics run, limp-home (RPR) active. |
| P2763 | Torque converter lock-up solenoid circuit — voltage low. Torque converter lock-up inhibited. |
| U0010 | CAN bus (IESCAN) counter overflow. Default values used, torque management during shifts disabled. |
Allison makes torque-converter automatic transmissions for trucks, buses and special vehicles (the 1000, 2000, 3000, 4000 series and others). Its control unit (TCM) stores faults, lights the CHECK TRANS lamp and, for serious faults, puts the transmission into a protective mode: it limits the gears or holds one. Codes can be read with a scan tool over CAN, and the manufacturer offers its own diagnostic software, Allison DOC.
The list above mixes short numbers and P0xxx-style codes. The first thing to know is whether a code is active (the fault exists now) or stored from the past.
Many complaints about poor shifting come from the fluid, not the electronics. The level is checked with the dipstick on a warm transmission in neutral with the engine idling, with the sump fluid at roughly 71-93 C (160-200 F), as the Allison manual describes. The fluid is normally a TES 295 or TES 668 synthetic unless your model says otherwise. Overheated, foamy or dark fluid is a reason to find the cause before repairing electrics.
If the transmission is in protective mode, will not shift, or CHECK TRANS comes on with slipping, stop: slip overheats the clutches quickly. If it shifts normally and the code is only stored, drive to a workshop and clear the code after the check.
Never tow a truck with an automatic on its drive wheels without disconnecting the driveshaft: there is no lubrication when the transmission is not running.
Either a protective mode after a solenoid fault or a fluid problem. Start with the fluid level and read the codes.
Read the codes and note whether they are active. The lamp means the TCM stored a fault that needs checking.
It is the brake switch signal. The page notes that on refuse trucks it blocks N-D shifting; check the switch and its signal.
Know the code number? Type it into the search — or paste the whole list from the scanner and we will show which fault is the real one.