Planar wide band O2 / Lambda sensor :

1) General sensor info :

2) Sensor connection info :

3) Wide-band lambda sensor technology :

The technology of the Bosch LSU-4 wide-band Lambda Sensor allows for accurate lambda ratio readings from 0.7 to 1.4 and beyond.

This wide lambda range is possible, because the closed loop control unit uses an almost linear I-Pump current. The wide-band sensor uses two different cells, an O2-ion pump-cell and a sensor-cell (Nernst type). The pump-current pumps enough O2-ions into the measuring chamber, which is shared by both cells, until the sensor cell shows 450 mV (Nernst cell lambda = 1) across it's electrodes. The lambda ratio is now almost linear proportional to the measured pump current.

 The NTK L1H1 sensor works on the same principal but with different calibration parameters

4) Definition of a lambda sensor :

A Lambda sensor is a device which measures the amount of the remaining oxygen in the exhaust gas. This is the reason why it is also referred to as an Oxygen or O2 Sensor.

The internal combustion engine typically burns hydrocarbons CxHy, where the longest chains are in the octane range of C8H18. With ideal combustion, all CxHx is being oxidized (burned) into carbon-dioxide CO2 and water H2O.

The chemical reaction looks like the following : CxHy + (x+y/4)O2 ==> xCO2 + (y/2)H2O

Since fuel is a combination out of different hydrocarbons, we define the air to fuel ratio in terms of it's mass (weight of molecules). The stoichiometric ratio for gasoline is 1 lb gasoline and 14.7 lb of air (containing 21 % of Oxygen). The volume ratio at 1 bar air-pressure would be about 4500 liter air for 1 lb of fuel.

If you take the results of the divisions M(air) / M(fuel),  the mass units will cancel out of the equation and ratios are the result. If you take both ratios and compare them you get the lambda value, which is not fuel specific anymore as a result.

Note : Stoichiometric ratio is the exact amount of chemicals to produce a theoretically ideal chemical reaction.

5) Lambda sensor range diagram :

This should proof the importance of the wideband technology in the analysis of most air fuel mixtures. By examining the left diagram it is shown in a graphical way how little air fuel information any narrow band tool has to offer. It is almost a switch which defines in a very precise way the stoichiometric point of the ideal air fuel ratio in accordance to the chemical reaction. Which is neither the point of most power nor better fuel economy. It is very easy for conventional fuel injection system to bounce within the closed loop operation range, right around this ideal measuring point.

The wide band lambda sensing technology is the only accurate way to determine the proper operation of your fuel injected or carbureted engine. The AFM-1 can be used to measure most air fuel ratios and can be used to control fuel injections by means of the programmable Lambda sensor simulation outputs.

Here is a side by side comparison of a Bosch LSU-4 wide band sensor (left) and a Bosch LSF-4 narrow band  sensor (right).

LSU-4 wide band sensor, including narrow band range (dark green)	LSF-4 narrow band sensor range

6) Lambda sensor use and care :

Install the sensor in a minimum of 10 deg upward position to avoid the trapping of condensation in it. It should be placed close to the engine to improve reaction speed for close loop control applications, but after a turbo, since the change in exhaust gas pressure will alter the reading. Also place it before any catalytic converter. Make sure it does not exceed the internal thermal limits, to be detected with the AFM-1 windows application.

Any in the exhaust stream installed sensor should be connected and have the sensor heater operated while the engine is running. The heater on with a cell temperature of 750 degC will self clean the sensor and avoids the deposition of carbon deposits or like.

Do not run the engine with any leaded fuel since the introduction of heavy metal-based chemicals will significantly shorten it's lifetime.

Readings can be altered by O2 being sucked back into the tail end of a straight through single cylinder exhaust pipe when placed near the end.
A source of O2 introduced by a leaky exhaust manifold or exhaust pipe or O2 being pumped into the exhaust stream before the sensor will lead to altered readings as well.
Misfiring will cause a similar effect due to the introduction of excess O2 into the exhaust stream

7) Sensor compatibility information :