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I had an early failure of one of the two lambda sensors in my 2011 Toyota Yaris that was driven for approximately 40 000 - 50 000 km at the time of failure. Fortunately, this was replaced for warranty. I became naturally curious why the lambda sensor failed.

The dealership offered no explanation for the failure, and I do not have the failed component so I cannot take a look at the old lambda sensor.

So, why would a lambda sensor fail?

Might it be a sign that there is something else defective in the car, or is the likely cause a manufacturing defect in the lambda sensor?

Or is it just normal wear and tear that a lambda sensor fails so early?

I assume the car has a heated lambda sensor as it's a quite recent car. According to Wikipedia, a heated lambda sensor fails due to catalyst depletion, but if this was really the failure mode then why would the catalyst deplete faster than usually?

According to Wikipedia, heated sensor lifetime is typically 160 000 km, from three to four times as much as my sensor lifetime.

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  • Other problems I've seen with O2 sensors failing is a poor placement; I've heard of some that are angled upwards which allow residual moisture to concentrate inside of the sensor, leading to sensor element failure (see here). Granted, that was an aftermarket part design flaw, but it's not inconceivable that a vehicle manufacturer could also have design flaws. That said, it's also not inconceivable that your original O2 sensor was just a lemon and failed early. "Lifetimes" are average values.
    – Shamtam
    Commented Dec 24, 2015 at 17:37

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Lambda sensors have several different failure modes.

  1. Heater element. The heater element is a resistive material that resists electron flow thus producing heat. This is the most common cause of early failure. The resistor burns through opening the circuit.

  2. Failure of the catalyst material. Usually caused by contaminates coming from the engine. Very uncommon early failure.

  3. Failure of the circuits connecting the electrical circuits connecting the sensing electrodes to the PCM.

  4. Contaminates on the outside of the sensor, plugging the air inlet vents.

The onboard testing done by the PCM is quite thorough on these sensors. It has many trouble codes that are used to describe the various failures.

This vehicle has two lambda (fuel mixture) sensors. They are very different, the one ahead of the catalyst is wide band type capable of reporting a fairly wide range of fuel mixtures. The one after the catalyst is a narrow band type capable of reporting mixture at stoichiometric. However, failure modes are similar, with some added circuit tests for the much more complicated wide band type.

Note: Some technicians poorly understand how these sensors work and how to test them. Inaccurate training over the years has caused confusion about how this sensor works. Most technicians are doing little testing; they are relying on the trouble code which works most of the time.

If you can provide the failure code the cause can be narrowed down.

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  • Unfortunately, I don't exactly recall the exact failure code as it failed over one hand half year ago, but if I recall correctly, it was caused by (1) the rear sensor and (2) due to an incorrect voltage, but I don't recall if the voltage was too low or too high. The symptom was that the check engine light was on and when I tested it with an OBD scanner, it showed a rear sensor incorrect voltage failure code. I don't believe it's a resistor failure, as I suspect the heating circuit failure would have a different failure code than an incorrect voltage failure code.
    – juhist
    Commented Dec 24, 2015 at 19:10
  • I googled to see if any of the failure codes seemed familiar, and P0136 seemed to sound the most familiar. I'm pretty sure it was P0136 but because this is just recalling from my memory, I'm not 100% certain. So, this would be the low voltage code for the rear sensor.
    – juhist
    Commented Dec 24, 2015 at 19:17

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