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E46 M3 exhaust sensor
- Thread starter Imraan
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tarintino
New member
2rin said:
Wikipedia is awesome!
Automotive oxygen sensors, colloquially known as O2 sensors, make modern electronic fuel injection and emission control possible. They help determine, in real time, if the air fuel ratio of a combustion engine is rich or lean. Since oxygen sensors are located in the exhaust stream, they do not directly measure the air or the fuel entering the engine. But when information from oxygen sensors is coupled with information from other sources, it can be used to indirectly determine the air-to-fuel ratio. Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to enabling electronic fuel injection to work efficiently, this emissions control technique can reduce the amounts of both unburnt fuel and oxides of nitrogen entering the atmosphere. Unburnt fuel is pollution in the form of air-borne hydrocarbons, while oxides of nitrogen (NOx gases) are a result of combustion chamber temperatures exceeding 1,300 kelvin due to excess air in the fuel mixture and contribute to smog and acid rain. Volvo was the first automobile manufacturer to employ this technology in the late 1970s, along with the 3-way catalyst used in the catalytic converter.
The sensor does not actually measure oxygen concentration, but rather the difference between the amount of oxygen in the exhaust gas and the amount of oxygen in air. Rich mixture causes an oxygen demand. This demand causes a voltage to build up, due to transportation of oxygen ions through the sensor layer. Lean mixture causes low voltage, since there is an oxygen excess.
Sensor failures:
Normally, the lifetime of an unheated sensor is about 30,000 to 50,000 miles (50,000 to 80,000 km). Heated sensor lifetime is typically 100,000 miles (160,000 km). Failure of an unheated sensor is usually caused by the buildup of soot on the ceramic element, which lengthens its response time and may cause total loss of ability to sense oxygen. For heated sensors, normal deposits are burned off during operation and failure occurs due to catalyst depletion. The probe then tends to report lean mixture, the ECU enriches the mixture, the exhaust gets rich with carbon monoxide and hydrocarbons, and the fuel economy worsens.
Leaded gasoline contaminates the oxygen sensors and catalytic converters. Most oxygen sensors are rated for some service life in the presence of leaded gasoline but sensor life will be shortened to as little as 15,000 miles depending on the lead concentration. Lead-damaged sensors typically have their tips discolored light rusty.
Another common cause of premature failure of lambda probes is contamination of fuel with silicones (used in some sealings and greases) or silicates (used as corrosion inhibitors in some antifreezes). In this case, the deposits on the sensor are colored between shiny white and grainy light gray.
Leaks of oil into the engine may cover the probe tip with an oily black deposit, with associated loss of response.
An overly rich mixture causes buildup of black powdery deposit on the probe. This may be caused by failure of the probe itself, or by a problem elsewhere in the fuel rationing system.
Applying an external voltage to the zirconia sensors, e.g. by checking them with some types of ohmmeter, may damage them.
Some sensors have an air inlet to the sensor in the lead, so contamination from the lead caused by water or oil leaks can be sucked into the sensor and cause failure.
Symptoms of a failing oxygen sensor includes:
Sensor Light on dash indicates problem
Increased tailpipe emissions
Increased fuel consumption
Hesitation on acceleration
Stalling
Rough idling
are you sure the sensor needs replacing? often something like a vacuum leak can bring up sensors but they are not the problem...
2rin said:
If you have no problems then leave it for now...
I take it the codes were cleared after reading? then you can take it back in a month or so have it read again to see if the same code comes up... if it does come up again you can think of replacing it... random codes are often thrown it does not always mean there is a problem...
codes are very useful to help find a problem but they cant be trusted 100%
I know this is an old thread but having recently changed mine on my old 325i I thought I would share some info.
I too did not have any indication of there being something wrong with the sensor. I also didnt think there was any lack of power or bad consumption. I just thought the lack of power was due to it being old. (its a 2002 IIRC)
I changed the sensor and it feels like a totally different car. It revs alot quicker, fuel consumption has improved andit even sounds different believe it or not.
So my suggestion if the fault shows up again, replace it.
I too did not have any indication of there being something wrong with the sensor. I also didnt think there was any lack of power or bad consumption. I just thought the lack of power was due to it being old. (its a 2002 IIRC)
I changed the sensor and it feels like a totally different car. It revs alot quicker, fuel consumption has improved andit even sounds different believe it or not.
So my suggestion if the fault shows up again, replace it.
