A
Adrian Tuddenham
- Jan 1, 1970
- 0
I have been testing a Bosch automotive exhaust gas oxygen sensor of the
zirconium dioxide type, which I suspect is faulty. There are four
connections to it: two wires to a floating heater element, which require
12v of no particular polarity; one sensor output wire and one sensor
earthing connection to the body of the device.
The heater correctly takes about 1.7A when cold, falling below 1A as it
warms up. The sensor is supposed to give readings between +0.2V and
+0.8v when exposed to exhaust gases, the voltage becoming more positive
with decreasing oxygen level. Instead, it gives readings between -0.8v
and -0.2v, with the voltage becoming more positive with decreasing
oxygen levels. In other words, the readings are behaving correctly but
are displaced about 1.0v negative.
According to various websites, this is typical behaviour for a sensor
which has become contaminated with silicone residue, and the obvious
solution is to replace it. However, I can find no source for such a
contamination and some websites imply that the contamination might be on
the reference surface of the zirconium oxide 'thimble', not on the side
exposed to the exhaust gasses.
My question is: does anyone know which side of the sensor is the
contaminated one when the voltage is displaced negative?
I realise this is not exactly a 'design' problem, but I think that I
shall only get a proper answer, as opposed to hearsay and guesswork, by
asking designers who have actually worked with such devices.
[I have already eliminated bad earthing contact between the exhaust
system and the engine, which is the commonest cause of a spurious
voltage readings. The vehicle is not consuming large quantities of
coolant, so anti-freeze contamination is not very likely. To the best
of my knowledge no repairs have been done with silicone sealants]
zirconium dioxide type, which I suspect is faulty. There are four
connections to it: two wires to a floating heater element, which require
12v of no particular polarity; one sensor output wire and one sensor
earthing connection to the body of the device.
The heater correctly takes about 1.7A when cold, falling below 1A as it
warms up. The sensor is supposed to give readings between +0.2V and
+0.8v when exposed to exhaust gases, the voltage becoming more positive
with decreasing oxygen level. Instead, it gives readings between -0.8v
and -0.2v, with the voltage becoming more positive with decreasing
oxygen levels. In other words, the readings are behaving correctly but
are displaced about 1.0v negative.
According to various websites, this is typical behaviour for a sensor
which has become contaminated with silicone residue, and the obvious
solution is to replace it. However, I can find no source for such a
contamination and some websites imply that the contamination might be on
the reference surface of the zirconium oxide 'thimble', not on the side
exposed to the exhaust gasses.
My question is: does anyone know which side of the sensor is the
contaminated one when the voltage is displaced negative?
I realise this is not exactly a 'design' problem, but I think that I
shall only get a proper answer, as opposed to hearsay and guesswork, by
asking designers who have actually worked with such devices.
[I have already eliminated bad earthing contact between the exhaust
system and the engine, which is the commonest cause of a spurious
voltage readings. The vehicle is not consuming large quantities of
coolant, so anti-freeze contamination is not very likely. To the best
of my knowledge no repairs have been done with silicone sealants]