What does it mean?
P1891 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: A/T Start Clutch Control System Malfunction . This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms
- Judder or shudder when pulling away from a standstill, worst on a light throttle
- Engine revs climb without matching acceleration, especially uphill
- Delayed or harsh engagement when selecting Drive or Reverse
- Malfunction indicator lamp on, sometimes with the transmission warning lamp flashing
- Burnt smell from the transmission fluid after repeated slipping
- Default (limp) operation restricting speed and ratio range
Likely causes
- Worn start clutch friction material
- Start clutch pressure control solenoid contaminated, sticking or electrically faulty
- Degraded, low or incorrect-specification transmission fluid
- Clogged filter or screen restricting the start clutch feed circuit
- Open, short or high resistance in the solenoid control circuit
- Valve body wear letting the start clutch apply pressure bleed away
- Faulty pressure sensor or module control strategy fault
How to fix it
- Check the fluid level and condition, and confirm the correct fluid specification was used at the last service
- Read all transmission codes and freeze frame data before clearing
- Road-test from a standstill several times while logging engine rpm, input speed and start clutch pressure
- Test the pressure control solenoid resistance and command it with a bidirectional tool
- Change the fluid and clean or replace the filter/screen if contamination is found, then reassess
- Reset and relearn the transmission adaptives after the fluid service
- If slip remains with correct pressure, plan internal repair of the start clutch assembly