O2 Sensor Faulty

Confirm, the trouble code is P0135.

Oxygen O2 Sensor, Bank 1,Sensor 1.

Mean that upstream O2 sensor is in faulty. 

A code P0135 may mean that one or more of the following has happened: 

1. O2 Heater element resistance is high 
2. Internal short or open in the heater element 

3. O2 heater circuit wiring high resistance 
4. Open or short to ground in the wiring harness

Questions?

1. Due to part failure

2. Emission too high?

3. Wiring problem that lead the sensor did not functioning correctly (power lost)?

Most probably, replace the right sensor will overcome this problem if the cause is (1). If other causes, the warning light is still ON. Normally cause (2) will trigger other trouble code together. Cause (3) could be identified with simple DIY check to confirm no electrical problem associated with 02 sensor.
Check the either the power is supplied to the sensor or not.

For Alphard ANH10W, there are two O2 sensor, upstream and down stream
Upstream sensor can be identified easily because it is located inside the engine bay.
Downstream sensor is located near underneath car at the exhaust system.

Upstream Oxygen Sensor Heater

Downstream Oxygen Sensor Heater

Changed both upstream and downstream oxygen sensor even the trouble code indicated the upstream sensor is malfunction. Because for me, this sensors work in a closed loop system. Better change both.

This sensor cost me RM490/pc.

New original Toyota about RM500 ~ RM700

Recond one (repair unit), RM200 ~ RM350 

Generic part , RM150 ~ RM250

Use only the new original Toyota sensor because there are some report/claim by them who use recond/generic part, the engine light warning will ON after 2 weeks with same trouble code P0135.