P0721

DTC P0721
Downshift safety monitoring.

Possible causes by suggested order of priority:
- Engine management ECM engine speed fault.
- connectors C243,EAT C193 .
- Open circuit shaft speed sensorC193/14 (B) to C193/42 (R).
- Open circuit C243/E (K) to C193/42 (R).
- Open circuit C243/F (B) to C193/14 (B).
- Shaft speed electrical interference.
- Shaft speed sensor fault.
- Torque converter mechanical fault.

Engine management ECM engine speed fault.
CHECK THE FOLLOWING:
- Read ECM fault codes and diagnose any engine speed, crankshaft sensor or related fault codes set.
POSSIBLE FAULTS
- Fault codes set in engine management ECM.

Connectors C243,EAT C193.
- Check for connector not correctly latched, backed out pins, damaged pins, corroded pins

Open circuit shaft speed sensorC193/14 (B) to C193/42 (R).
- Check resistance > 1M Ohm

Open circuit C243/E (K) to C193/42 (R).
- Check resistance > 1M Ohm

Open circuit C243/F (B) to C193/14 (B).
- Check resistance > 1M Ohm

Shaft speed electrical interference.
- Use Live Data reading to display the output shaft speed as measured by the transmission ECU
CHECK THE FOLLOWING:
- With the engine running and the position switch in 'P' the shaft speed should measure 0 RPM.
- If the reading is not 0 RPM then there may be a problem with electrical interference.
- Check the connections to the screen around the output shaft sensor wiring.
POSSIBLE FAULTS
- Faulty output shaft sensor wiring.
- Faulty output shaft sensor

Shaft speed sensor fault.
- Use Live Data reading to display the output shaft speed as measured by the transmission ECU
CHECK THE FOLLOWING:
- Monitor the road speed (from the vehicle speedometer) and the output shaft speed while driving on the road or on a rolling road.
- The two readings should maintain the same ratio. If one reading doubles so should the other reading.
- If the readings do not maintain a fixed ratio the output shaft sensor may be faulty.
POSSIBLE FAULTS
- Faulty output shaft sensor

Torque converter mechanical fault.
- Use Live Data reading to display the output shaft speed as measured by the transmission ECU.
CHECK THE FOLLOWING:
- Monitor the road speed (from the vehicle speedometer) and the output shaft speed while driving on the road or on a rolling road.
- The two readings should maintain the same ratio. If one reading doubles so should the other reading.
- If the readings maintain a fixed ratio the torque converter may be faulty.
POSSIBLE FAULTS
- Transmission torque converter mechanical fault.