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Author Topic: Lambda Sensor  (Read 6559 times)

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Fuse 19

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Lambda Sensor
« on: 14 August 2006, 13:04:15 »

The lambda sensor is known by a number of different names i.e.

Oxygen sensor
Lambda sensor
Exhaust Gas Oxygen Sensor (EGO)
O2 Sensor

etc

This is a simple device which sits in the exhaust front pipe or manifold and monitors the exhaust gases for the presence of oxygen.




Its operation is fairly simple and its constructed from a plate of ceramic or metal with a platinum coating. Some alternative types are constructed using a Zirconium dioxide material.

The device produces a low voltage (between 0.2 and 1.4 V depending on the sensor type) which is related to the oxygen content. Reality is that the non-linearity of the voltage is such that the ECU can only really get a lean/rich indication from the sensor.

On lean burn engines a different type of sensor is required as the mixture is run deliberately weak when cruising, this requires the use of a wide band oxygen sensor. No Omega uses this method of control.

It is important to note the a lambda sensor only works when its hot and as such normally includes a heater to get it up to temperature quickly. The omega ones as a result appear as two types:

3 Wire - Used on the V6, One wire is the sensor output with the other sensor output being earthed via the sensor body to the exhaust. The two additional wires are the heater assembly.

4 Wire - Used on the 4 pots, two wires for the sensor and two for the heater.

The heater resistance is normally around the 4-10 ohm mark.

The ECU controls the mixture by monitoring the sensor reading, if the sensor is reporting the mixture as lean then it rich-ens the mixture by extending the fuel injector period (see other FAQ on fuel injectors), until the sensor flips to the rich indication, it then weakens the mixture until it again reports a lean mixture, this repeats continuously.

Later units have 2 or 4 lambda sensors, this helps to reduce pollutants further by monitoring the oxygen content before and after the cat and comparing the two values.

Thing to note:

1) Lambda sensors rarely fail but, they can be confused due to blocked or leaking exhausts. A leaking exhaust may well pop gas causing a ticking noise out as the pressure rises due to an exhaust stroke passing through it but, this pressure pulse is also followed by negative pressure after the exhaust valve has shut which draws air in.

2) The lambda sensor will not work until its VERY hot and hence the presence of a heater to speed up the heat-up period. If the heater is faulty then a heater coil fault may be flagged, in the case of the V6 the ECU cant monitor the heater directly and is probably actually reporting a slow switching time from the sensor (i.e. its a bit cooler then the optimum). As such you would need to measure the resistance of the heater coil to determine if it is really this at fault.

3) These can be sods to remove and replace, they really need soaking in a very good penetrating fluid.....often the threads are stripped from the sensor body on removal and the front pipe threads then need chasing out.
« Last Edit: 04 February 2010, 10:32:29 by jimbob »
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