Tip & How-To about Mercedes-Benz E-Class

Oxygen (Lambda) sensor

1.12) Oxygen (Lambda) sensor

What is it? This is an electrical device that measures electronically the amount of oxygen in the exhaust.

Where is it located? The device looks, externally, a bit like a spark plug set into the exhaust manifold. It is screwed into the manifold and is identified by a thick wrap cable connected to its top.

How does it work? There are generally two types of oxygen sensor. The first has only one wire to it. This is the voltage output wire, the metal body of the sensor provides the 'ground' in the circuit. The second type of sensor has four wires within the thick cable. Two of these wires generally of the same colour (most often white) are part of electrical heater circuit built into the body of the oxygen sensor (it only works when very hot). The other two wires (often grey and black) are connected to the oxygen sensing element and these send a cycling voltage output (0.1 to 0.9 volts) inversely proportionate to the oxygen levels detected, back to the ECU. If the engine is running very lean the oxygen levels in the exhaust are high and the sensor has low voltage; conversely if the engine runs rich the oxygen levels are low and the voltage output of the sensor is high.

On some systems there are two oxygen sensors, one on the exhaust manifold before the catalytic convertor, monitoring engine operation and one after the catalyst that measures the catalyst performance. With twin separate exhausts as with V6 and V8 engines it is possible to have four oxygen sensors.

Symptoms of faulty oxygen sensor

Associated OBD2 error codes DTCs: P0130 - P0167

Although perhaps seen as the last element in the chain of engine feedback sensors the significance of a faulty oxygen sensor should not be overlooked as it exerts a very strong influence on the ECU:-

· Fast/erratic idle, poor fuel economy - if the oxygen sensor, in error, reports to the ECU that the engine is running lean (oxygen levels are high) the ECU may respond by enriching the fuel mix. This causes the engine to have a lumpy idle at a higher than normal rate and also increases fuel consumption. (see additional note below)

· Hesitation and surging - signals from the oxygen sensor continue throughout the engine performance range so fault issues that manifest themselves at idle will occur at all engine speeds with performance consequences.

· Misfire and stalling - if the oxygen sensor reports that the exhaust oxygen levels are too low (i.e. engine running rich) the fuel mix might be reduced, through reduced injection times, to the point at which the engine misfires or stalls from being made too lean.

NEXT 1.12b) How to check and fix oxygen sensors

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2006 CTS 3.6 getting code P2097. What is the cause please?

DTC P2097 Post Catalyst Fuel Trim System High Limit Bank 1
Circuit Description
The wide band heated oxygen sensor (HO2S) measures the amount of oxygen in the exhaust system and provides more information than the switching style HO2S. The wide band sensor consists of an oxygen sensing cell, an oxygen pumping cell, and a heater. The exhaust gas sample passes through a diffusion gap between the sensing cell and the pumping cell. The engine control module (ECM) supplies a voltage to the HO2S and uses this voltage as a reference to the amount of oxygen in the exhaust system. An electronic circuit within the ECM controls the pump current through the oxygen pumping cell in order to maintain a constant voltage in the oxygen sensing cell. The ECM monitors the voltage variation in the sensing cell and attempts to keep the voltage constant by increasing or decreasing the amount of current flow, or oxygen ion flow, to the pumping cell. By measuring the amount of current required to maintain the voltage in the sensing cell, the ECM can determine the concentration of oxygen in the exhaust. The HO2S voltage is displayed as a lambda value. A lambda value of 1 is equal to a stoichiometric air fuel ratio of 14.7:1. Under normal operating conditions, the lambda value will remain around 1. When the fuel system is lean, the oxygen level will be high and the lambda signal will be high or more than 1. When the fuel system is rich, the oxygen level will be low, and the lambda signal will be low or less than 1. The ECM uses this information to maintain the correct air/fuel ratio.
Fuel trim biasing is used by the ECM to keep the post catalyst HO2S voltage within a range of 580-665 mV as possible. This allows optimal catalyst efficiency under light load conditions, such as at idle or a steady cruise. The ECM constantly monitors how lean or rich the fuel trim bias is commanded. If the ECM detects that the fuel trim bias is commanded rich for more than a calibrated amount, DTC P2097 or P2099 sets.

Air Fuel Wideband vs Oxygen Sensors O2 sensors The Demise of Shadetree...

Sep 01, 2016 | 2006 Cadillac CTS

1 Answer

a service on my Toyota Rav 4 2003 shows p1135 a/f sensor heater fault b1-s1 fault with lambda sensor. How does this affect car running is it safe?

OK a bit of background. The oxygen or lambda sensor determines the amount of air in the exhaust gases. It does this by producing a voltage inversely proportional to the amount of oxygen present. When the oxygen is low the voltage is about 1 volt and when the oxygen is high it is less than 0.1 volt. The ECU uses this feed back to continuously adjust the amount of fuel injected for combustion. These sensors only work effectively when they are hot. The manufacturers of sensors include a heater element within the sensor tip to preheat the sensor at start up when the engine is cold. Most modern oxygen sensors have four wires to them, two for the heater (often of the same color) and two for the oxygen sensor circuit. If the heater element fails the sensor is unable to work effectively when starting the engine up. In this case the sensor reports a low voltage which the ECU reads as "high oxygen in the exhaust" or a 'lean' condition and tries to compensate by injecting more fuel. When the engine eventually warms up and the exhaust gases get hot the sensor then begins to function and the ECU will reduce the amount of fuel being injected once more. It is perfectly safe to drive the vehicle. However if you are making lots of short trips in which the engine rarely gets to reach hot running conditions your fuel consumption will suffer badly as the ECU will be injecting way more fuel than you need. You will also find that your exhaust smells of un-burnt fuel and your idle maybe a bit fast and lumpy with the over rich injection cycles. Often a 'bad heater' can be just down to a bad connection due to dirt, or more often corrosion, in the plug/socket to the actual sensor and a few cycles of connecting and disconnecting it can fix it. Replacing a sensor is not catastrophically expensive, $100 or so for the part (Denso or NGK) but that can rise if the garage also fits it.

Jul 05, 2011 | 2003 Toyota RAV4

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It has a fault number p1051 and p1168 pls tell me what to do

p1051 and p1168:

P1051 A/F Sensor Heater (Added 29APR2007)
p1168 A/F Sensor Heater.

A/F Sensor The air fuel ratio (A/F) sensor like the oxygen sensor is used by the powertrain control module to measure the amount of oxygen in the exhaust. The PCM uses this data to control the air fuel mixture in the engine. The (A/F) sensor can meter fuel more accurately than an oxygen sensor. The A/F sensor changes current output by measuring the amount of oxygen in the exhaust. The A/F sensor operates at a much higher temperature than an oxygen sensor. The PCM measures the amount of current that is output by the A/F sensor and converts this current flow data to a voltage signal. When the mixture is lean and the oxygen content is high the voltage signal will be above 3.3V. When the mixture is rich and the oxygen content is low the voltage signal will be below 3.3V. When the mixture is at 14.7 to 1 the voltage signal will be at 3.3V. The heater circuit in the A/F sensor shortens the time required for the sensor to reach operating temperature and provides a more accurate signal.
The A/F error is like an Oxygen Sensor error. There could be a problem with this sensor or the wiring to it causing voltages to be out of specifications.

Jul 31, 2010 | 2003 Nissan Murano

2 Answers

can you tell me what a lambda sencer does and how does it affect the engine,as my engine light comes on but dosent stay on but when on reduces power.thank you it is a vauxhall astra club 2000 16v did not have vauxhall on list

Not sure, but I believe the lambda sensor is the feedback sensor, to determine if the mixture really is right.
On most cars that is the oxygen sensor I believe, and is located in the exhaust manifold or the top of the exhaust pipe.

Mar 30, 2010 | 1985 Volkswagen agon

1 Answer

oxygen sensor

An oxygen sensor, or lambda sensor, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analyzed.

Sep 06, 2009 | 2003 Chevrolet Silverado 1500

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