02 Sensor Heater Malfunction

I have a 96 toyota tacoma 4x4 2.7L truck. I just replaced the exhaust system. I put in a new catalytic converter also. Everything went in nicely, but now I have my check engine light coming on. I have an OBD II reader and found out what was causing the light to come on. The trouble code is P0135, O2 sensor heater malfunction. I think I might have put the sensor in upside down from what it was, if that is possible? Did the sensor go bad just from me taking it out? I was reasonably careful with it. Any thoughts or ideas would be appreciated!

You can’t put the sensor in up-side-down.

The heater circuits for O2 sensors are suseptable to thermal shock. So the fact that the exhaust system and catalytic converter were replaced may have provided better flow causing the exhaust gasses to heat the old O2 sensor faster causing this thermal shock.


No, you can’t put an O2 sensor in upside down. Not even with a lot of ingenuity. If you’re curious about how they work, the Wikipedia article http://en.wikipedia.org/wiki/Oxygen_sensor will tell you more than you ever wanted to know.

Check the wiring to make sure you haven’t damaged the harness somehow. Open the connector to the car’s wiring harness, check for bent/recessed pins (unlikely, but while you are in the neighborhood …), push the connector back together firmly. Clear the code and see if it comes back.

If the code keeps on coming back, check pricing on the internet. You almost certainly do not need a genuine Toyota part. Stores like Autozone will probably have an aftermarket option that is not too far from internet pricing. Replacement should be easy since you just had the previous sensor in and out.

Check the pigtail wiring of the sensor. Since they run in a hot enviornment, moving the wires around may have openned or shorted the heater wire. I do not know if this would be a 3 wire or 4 wire O2 sensor. If this is a 3 wire, ohm out the heater wire to the base. If it is a 4 wire, ohm out the heater hot wire to the ground wire.