Wideband versus Narrow Band O2 Sensor Signals

Wideband versus Narrow Band O2 Sensor Signals

By in Engineering

Traditionally combustion engine controllers have used narrow band oxygen sensors to adjust fuel mixture. They require no calibration making them ideal for factory engine controllers. However, they can only tell us if the exhaust stream is rich or lean. They cannot tell us how rich or lean which makes them poor for tuning applications. I’d like to see if there’s way a wideband sensor could be adapted to work in place of a narrow band. Then a factory engine controller could run without the need for installing a second wideband sensor to tune with.

Narrow band versus wide band Oxygen sensor

These tell the controller if there’s unburnt oxygen in the exhaust. Oxygen sensors tell us if there’s less oxygen in an exhaust system in reference to ambient air. Narrow bands can only tell us if there is more or less oxygen but not how much. That’s where wideband sensors come into play. They can give us a ratio of how much oxygen there is between exhaust and ambient air. This makes them a necessity when tuning applications where the fuel ratio requires excess fuel such as power enrichment.

Harness adapter

I am going to prototype on my 2001 Chevy Tahoe. Specifically for a bank one sensor which is used to adjust the fuel mixture. The controller is a widely used Delphi P59 based off MAP and MAF sensors for dynamic air flow and or speed density. A bit more detail than we need but this covers operation of most EFI vehicles pre torque management modeling which started around 2008?

Narrow Band Connectors

Connector in PCM harness to factory narrow band sensor.

Controller Connector Part# 12162144 Manufacturer Aptiv
Sensor Connector Part# 12162102 Manufacturer Aptiv

Wideband Connectors

The Bosch 4.9 and 4.2 are the industry standard wideband sensors. I have a 4.9 on hand which uses the following connectors:

Controller Connector: Part# D261.205.356-01
Sensor Connector: Part# 1928.404.687

Pinout for Bosch 4.9 Wideband Sensor from datasheet HERE

Controller Wiring

Narrow Band Theory of Operation

The narrow band sensor requires a input voltage supplied by the ignition circuit of a vehicle. This is ideally between 12.6V and 14.5V. Voltage in my application is supplied via the heater circuit pins. This energizes an element in the sensor to heat up the “sensor “Nernst cell” to operating temperature. It also provides input voltage for the sensor signal to be generated.

The sensor can be read once the plate / Nernst cell separating ambient air (reference) from exhaust gas operating temperature. As the sensor reaches that temperature the current draw of the heater circuit drops. If it does not the controller will trigger a fault for a faulty oxygen sensor circuit.

Electrons saturate the cell creating a sensor signal when exhaust gas has fewer oxygen atoms in reference to ambient air. The less oxygen in the exhaust, the richer the mixture, the higher the voltage. The more oxygen, leaner the mixture, the lower the voltage.

Narrow band signal

Narrow band process with a single Nerst cell creates a signal from approximately 200mV lean to 800mV rich. The controller then has a “fulcrum” value typically around 450mV. Under this value is considered lean, and over it is rich.

How much excess fuel or oxygen isn’t certain with this process. The controller meters fuel such that the sensor reading switches between rich and lean. Fuel trims / adjustments are made based off how frequently the sensor switches between rich and lean mixture, also known as a “cross count”.

NOTE: Some oxygen sensors utilizing the same narrowband process do not require the voltage input. I think the process is piezoelectric. However, in my automotive application the heater must be energized to get the sensor output.

A work in progress…

I’m currently storing my notes here. I’ve got some microcontrollers I plan to install both a wideband and narrow band in the same exhaust stream and compare the signals as read by a microcontroller. The plan is to use a ESP32 and stream the values via Bluetooth do a device where I can log them. Eventually a transfer function will be programmed into the ESP32 and output provided to the PCM with a separate wideband output for tuning and datalogging.

Matthew Jeschke

I've been hard on jeans since childhood when my single most important job was to stuff my Fisher Price camera in my pocket and set out to explore. My mission was to photograph animals I wanted to make pets such as squirrels, chipmunks, and rabbits. A sense of adventure propelled me deeper into the grassy fields of rural Nebraska. My trusty sidekick Domino (pet dog) was a great companion always by my side. An old Schwinn bicycle served my iron horse. We set our sights set on the distant horizon over which, somewhere, the rolling hills of Nebraska had to turn into mountains. Years later I landed on that distant horizon asked to make aerospace parts whatever those must be. I was a long ways from those squirrels and endless cornfields in Nebraska. I'm also few boot sizes bigger from those days, but still armed with my cameras and and a sense of adventure. Only this time I have a vast desert and dozens of mountain ranges to explore. The wilderness here hasn't much changed since the original Spanish colonists arrived nearly 500 years ago. Heck I imagine this place is not much different than when God created it. What has changed is the internet. Nobody grew up dreaming of being an internet sensation, rotary phones were still the big thing! The only viral videos to be found were on Saturday morning of Wile E Coyote chasing the roadrunner.

Comments are closed.