P2639Torque Management Feedback Signal A Low
- Generic OBD-II code · Powertrain
- Can trigger limp mode
- How the car detects it
- P2639 means the torque management feedback signal A stays below its valid range, so the transmission controller cannot read a usable torque confirmation from the engine. No manufacturer explains this exact code publicly. The closest documented relatives are Allison's P2637, where the TCM checks over the SAE J1939 data link whether the engine honours shift torque reductions, and Honda's P2638 on its nine-speed gearbox. If the feedback travels as a network message rather than a wire, a low value usually stems from a calibration mismatch between engine and transmission software or a missing message; on a hard-wired signal, check for a ground short. CARB requires such inputs to be tested against range limits. Shift quality may suffer and torque reduction may be disabled.
- What you may notice
- Transmission warning or stored code
- Firm or flared shifts
- Likely causes
- PossibleEngine and transmission software versions not matched
- PossibleTorque feedback message missing or corrupted on the data bus
- RareHard-wired feedback line shorted to ground
- Repair
- Workshop only · Usually a job for a workshop.Typical cost: €80 – €500
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.