P2644: Torque Management Feedback Signal B High

P2644 reports that torque management feedback B exceeds its upper range limit. No manufacturer publishes a code-specific description. The closest documented case is Allison's P2641: a 2013 Cummins ISX12 calibration reported more torque than the low-range cap allowed, and Mack and Volvo trucks showed the same code under heavy load until the engine software was updated. A reading that is not just above the cap but beyond any valid value points to the same family of problems, namely engine software that scales or encodes the torque message differently from what the transmission expects, or a wired signal shorted to voltage. Low ranges may be locked out and the warning lamp lit. P2643 is the low fault, P2640 the high fault of signal A.

Symptoms

• Transmission warning lamp on
• Low ranges blocked
• Shift quality reduced

Most likely causes

• Engine software sends torque with a scaling the transmission does not expect
• Engine calibration older than the level required by the transmission maker
• Wired feedback line shorted to voltage

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the fluid level and condition
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Read the input and output speed in live data
4. Check the connector and wiring
5. Check for other related engine codes
6. Consult the manufacturer's procedure for the transmission

Good to know

• It can trigger limp mode.

What each character of P2644 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 6: Control modules and outputs
• 44: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2644?

Drive gently to a repair shop. If it slips, you hear clunks, or it loses its gears, do not keep driving.

What causes code P2644?

The most common causes are: engine software sends torque with a scaling the transmission does not expect; engine calibration older than the level required by the transmission maker; wired feedback line shorted to voltage.

Related codes

• P2641Torque Management Feedback Signal B
• P2642Torque Management Feedback Signal B Range/Performance
• P2643Torque Management Feedback Signal B Low
• P2640Torque Management Feedback Signal A High

Sources

• law.cornell.edu: 13 CCR 1968.2
• static.nhtsa.gov: MC 10155490 9999
• static.nhtsa.gov: MC 10203974 0001

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.