What does it mean?
P1644 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Traction Control Delivered Torque Output Circuit Malfunction .
Symptoms
- MIL on together with traction control and often ABS warning lamps
- Traction control disabled, or intervening briefly with no wheel slip
- Engine does not reduce torque when a wheel spins, so the car scrabbles on wet or loose surfaces
- Momentary power loss or a harsh shift as the modules disagree
- Cruise control refuses to engage or drops out
Likely causes
- Open, shorted or high-resistance torque signal wire between the PCM (powertrain control module) and the traction control module
- Corroded, backed-out or spread terminals at either module connector
- Poor common ground between the engine and traction control modules
- Internal failure of the ABS/traction control module output stage
- Failed driver inside the PCM
- Harness damage from a previous repair, an aftermarket accessory tapped into the circuit, or rodent damage
- Low system voltage from a weak battery or poor battery terminal connections
How to fix it
- Scan every module, not just the engine, and record the traction control codes and freeze frame data
- Unplug and inspect both module connectors for green corrosion, moisture and loose terminal tension
- Check the torque signal wire end to end for continuity and for shorts to ground and to battery voltage
- Voltage-drop test the power and ground feeds of both modules and confirm battery condition
- Back-probe the signal and wiggle the harness, or drive the vehicle while logging, to catch an intermittent fault
- Repair the damaged harness section and clear both memories before retesting
- Consider module replacement and coding only after the wiring is proven good