How O2 Wideband Controllers work

It cannot be overstated just how important it is to get reliable and accurate data from your wideband air-fuel ratio meter. And while there is a multitude of different wideband O2 sensors on the market and they don’t all play nicely together.

You can’t, for example, take a Bosch sensor and use it with an NTK controller or vice versa. In fact, you cannot even take two series of Bosch sensors like the Bosch LSU 4.2 and the Bosch LSU 4.9 sensor and use them with the same controller. Your wideband controller must be matched with the specific sensor type it was designed for.

Before discussing the different types of sensors, let’s start at the beginning and look at what narrowband and wideband sensors are and how they work.

Narrowband O2 Sensors

Narrowband O2 sensors typically have either 1,2,3 or 4 wires and they all work basically the same way; the output signal will flip from 0V to 1V when the air-fuel ratio goes richer than the stoichiometric air to fuel ratio of 14.7:1, it then flips back to 0V when the measured air-fuel ratio goes leaner than the stoichiometric air-fuel ratio of 14.7:1 or lambda of 1.

This is important to know – because it means a Narrowband O2 sensor does not know and cannot tell you if an engine is at 13:1 air-fuel ratio, 12:1, 14:1, or any specific air-fuel ratio for that matter. It only knows 2 values: lean of the stoichiometric air-fuel ratio and lean of the stoichiometric air-fuel ratio.

TIP: If you have not watched our on Ignition Timing vs Air-Fuel Ratio’s effect on output power – now is probably a good time do it because in that video we explain why selecting the correct air-fuel ratio is so important (spoiler alert: it’s much less about making horsepower and much more about engine longevity).

So, if a Narrowband O2 sensor cannot tell us any specific air to fuel ratios (apart from 14.7:1) and we know that running an engine at full noise with an air-fuel ratio of 14.7:1 is potentially catastrophic – then what are narrowband O2 sensors for?

The simple answer to that question is “tailpipe emissions”. We are not going to go into detail on how to tune an engine to meet specific emissions standards here, but broadly speaking to pass most emissions tests you need a catalytic converter in your exhaust. A catalytic converter is made up of multiple materials each with the specific purpose of converting potentially harmful byproducts of combustion into harmless carbon dioxide, water, or Nitrogen. For the catalytic converter to work effectively it must be receiving a pulsating exhaust gas flow of mixtures rich and then lean of stoichiometry.

Incidentally, this is exactly why in years gone by manufacturers would turn off O2 control under full engine load and high RPM. Not because the engine would make less power, but rather for the O2 control to work it relied on the air-fuel ratio oscillating around 14.7:1 which is far too lean for engine reliability at high horsepower. What the O2 narrowband sensors are not useful for – is tuning an engine.

Wideband O2 Sensors

Wideband O2 sensors typically have 5 or 6 wires and require some very specific electronic circuitry to control them. When controlled correctly wideband O2 sensors are capable of accurately showing air-fuel ratios anywhere from 6:1 to over 20:1 which makes them the only choice for measuring air-fuel ratio when tuning an engine.

With a wideband O2 sensor the ECU can be monitoring the actual air/fuel ratio, checking back against the tuner’s desired ratio, and then make changes to make sure the Target and Actual are always the same. We can even perform what we call “Long Term Learning” so that each time the Target and Actual Air/fuel ratios don’t match the ECU will record and apply a correction. This way the ECU is not trying to correct the same error over and over again. And the best thing is – as you drive the car the tune gets better and better!

Why would there be an error you ask? This could be down to different climatic conditions like temperatures and pressure, it could be related to fuel temperature, intercooler efficiency on the dyno compared to on the road or parts of the fuel map that are hard to simulate on a dyno.

It would be a hugely time-consuming task to tune for every potential temperature for every sensor on every custom modified engine, and it’s for this exact reason why a wideband oxygen sensor and long-term fuel learning are a must for a performance car.

With a wideband Oxygen sensor, you can also set operating limits to protect the engine. For example, if the RPM was higher than 4000 and the boost pressure is higher than 15 pounds you could set an Engine Protection Limp State if the AFR is leaner than say 13:1 (or whatever you choose).

This, coupled with the increased fuel economy and performance that Closed Loop O2 control offers makes choosing a wideband oxygen sensor the obvious choice.

Haltech O2 Wideband Kits

Let’s take a look at Haltech’s current offering of Wideband O2 sensors, the most common of which is a CAN-connected wideband unit.

This unit uses a Bosch LSU 4.9 wideband O2 sensor and has been the mainstay of Haltech’s wideband o2 controller offerings for a number of years. It’s safe to say it’s one of the most tried and true wideband O2 sensors and controllers on the market today. It readily and repeatedly reads air-fuel ratios down to 10.5:1 and when installed correctly has a long sensor life on most fuel types.

Note we said “most” fuel types and not “all”. That’s because the fuel type is one of the limiting factors of these sensors. Fuels that are not petrol or gasoline and air-fuel ratios that are richer than 0.7 lambda can significantly shorten a Bosch LSU 4.9 sensor life.

And that is where the NTK sensors take over. The NTK LZA08 sensor offers a much more robust sensor life at both richer mixtures and with alternate fuel types like methanol and race gas.

Much like the Bosch wideband, the NTK units come in a single channel and dual channel variation and will read reliably all the way down into the 2:1 air-fuel ratio range for methanol drag cars – that’s more than twice the range of the Bosch sensor.

Both the Bosch and NTK Wideband Controllers are auxiliary CAN devices which means they have their own control system and processor built into the control unit and transmit the air-fuel ratio data back to the ECU via a communications protocol known as CAN.

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