P2643
Torque Management Feedback Signal B Low
Powertrain torque management
Generic OBD-II
Medium
What it means
P2643 means the control module detected a low signal on torque-management feedback circuit B, the line the engine and transmission controllers use to coordinate engine torque during shifts. A fault here usually shows up as rough or delayed shifting and reduced power, and the transmission may protect itself with a limp mode. It does not stop the engine from starting.
Medium
Can I keep driving? Usually drivable, but shift quality and power delivery may be off and the transmission can drop into a protective limp mode.
Common symptoms
What you'll notice
- Check-engine light on
- Harsh, delayed, or erratic shifts
- Reduced power or a flare in engine speed during gear changes
- Transmission may enter limp (limited-gear) mode
Common causes
Most likely first
- Low voltage or short to ground in the torque-management signal circuit between the ECM and TCMLikely
- Corroded or loose connector at the ECM or TCMCommon
- Wiring chafe or damage in the signal harnessCommon
- Faulty transmission control moduleLess often
- Faulty engine control module (least likely)Less often
How to diagnose & fix
Work through it in order
- Read freeze-frame data and check for companion torque-management or transmission codes.
- Inspect the ECM-to-TCM signal wiring and connectors for shorts, corrosion, or damage.
- Check reference voltage and ground on the affected circuit.
- Verify the torque-management signal values with a scan tool against expected ranges.
- Repair the wiring or connector; replace the TCM or ECM only if confirmed faulty. Clear and re-test.
FAQ
Quick answers
Is it safe to drive with P2643?+
Short trips are generally okay, but expect rough shifts or reduced power, and the transmission may limit itself to protect internal parts. Have it checked before hard or extended driving.
Can I just clear P2643?+
It will come back until the signal circuit or module is repaired. Clearing does not restore proper torque coordination between the engine and transmission.
Related codes
Often seen with P2643
Read & clear P2643 yourself
Scan your car, confirm the code, and clear it once it's fixed — with OBD DashX on your phone.
✓ Verified name — SAE J2012 / ISO 15031-6Guidance reviewed by OBD DashX