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.
