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Failed Smog Test

Toyota Sienna failed smog for PO125 PO135 and PO155

My 1999 Toyota sienna failed Smog Test. With a trouble code machine I got codes PO125 &PO135 & PO155.

I replaced A/F sensor B1-1(denzo) and B2-1 and o2 heated downstream sensor and CTF all brand new. I replaced the termostat as well. Why am I still getting the same trouble codes after 3-4 miles? Please help me. Thank you.


You've replaced several emission sensors with no change in Check Engine Light results. Often simply replacing a trouble component does not mean the system has been repaired. In this particular case we recommend making sure each sensor is communicating with the ECU properly, and reference voltage & ground is available at each sensor (as required).

When more than three components are indicated to be failing we often notice a ground problem or ECU reference voltage problem.

The following are general trouble code descriptions:

OBD II DTC P0125 - Insufficient Coolant Temperature For Closed Loop Fuel Control

Engine coolant temperature (ECT) sensor indicating engine has not reached closed-loop operation required temperature within 160 seconds. Possible faults may include faulty ECT sensor, defective ECT wiring or harness, low engine coolant levels, stuck open thermostat.

OBD II Trouble Code DTC P0135 - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)

Possible faults include high O2 Heater element resistance, high wiring and/or harness resistance, open or short in the O2 Heater Ground circuit.

Since you've already replaced both bank 1 and bank 2 sensors, we highly recommend checking the ground source.

OBD II Trouble Code DTC P0155 - 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

(same as P0135 except for Bank 2)

posted by SmogTips Support 09-05-2012 01:55 PM

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