Wiring Wideband O2 Sensors


Goblin Guru
This has been a popular topic recently, so I'll attempt to write something up that can be referenced rather than adding information piecemeal in response to various questions.

What is an O2 (oxygen) sensor?
Spark ignition engines must inject a precise amount of fuel based on how much air enters the cylinder. Too little fuel (lean) can cause the engine to run hot or to knock, and too much fuel can reduce power and foul spark plugs. O2 sensors are necessary to provide feedback to the computer as to whether more or less fuel is needed for a given airflow.

O2 sensors measure the amount of unburnt oxygen in the exhaust stream and output a calculation that indicates the ratio of air to fuel. Under steady state, the engine tries to minimize over- or under-fueling, where excess fuel or air would pass through the cylinder unincorporated into the combustion process. For pure gasoline, the ratio is about 14.7 parts fuel to 1 part air, also written as 14.7:1 AFR. For E85, it's about 9.8:1, and for methanol around 6.5:1. To obviate the need to specify fuels and their corresponding AFRs, it can be easier to refer to O2 sensors as measuring lambda (λ), or the ratio of the actual AFR to the stochiometric AFR (a ratio of a ratio, yes, but it does simplify things). When trying to make power, especially with forced induction, a richer fuel mixture is needed to keep things cool and allow for more timing- something like 11.5-12.5 AFR on gasoline, 7-8 AFR on E85, or, more simply, 0.8 λ.

What's the difference between a narrowband and wideband?
There are two types of O2 sensors: narrowband and wideband. A narrowband sensor can really only quantify between 0.99-1.01 λ, or like 14.6-14.8 gasoline AFR. With a 0-1v output, steady state stochiometric is seen by the ECM as a rapidly and evenly alternating lean-rich cycle. Too rich would tend to show more measurement time at the low end of the output range, and vice versa. Because this sensor can't tell the difference between anything richer than 0.99 λ, it cannot be used effectively to tune for power, which is where the wideband sensor comes in.

The wideband sensor can accurately quantify a wider range of λ, thus its name. The common Bosch LSU4.9 sensor can read down to 0.65λ, or about 9.6 gasoline AFR or 6.8 E85 AFR. With a 0-5v output, the ECM and/or tuning computer can measure rich lambda and more accurately track the fueling required to maintain the target air-fuel ratio.

So what?
The 2008-2010 Cobalt SS/TC with LNF engine is the only Cobalt that came from the factory with a wideband O2 sensor. While I don't have an LNF, I have read and been told that it's not the most accurate or reliable. All stock Cobalts, turbo or not, have a stock narrowband O2 sensor after the catalytic converter (also referred to as HO2S2, heated O2 sensor 2), whose sole purpose is to measure catalytic converter efficiency. All non-LNF Cobalts have a stock narrowband O2 sensor pre-cat (HO2S1).

Whether you have an LNF and want to add an aftermarket wideband O2 sensor/gauge or have any other motor and want to do some tuning, this leads to the topic that led to the creation of this post:

How to add an aftermarket Wideband O2 sensor

0. Purchasing
You will need to purchase, at minimum, a sensor, a controller, and a wiring harness. AEM and Innovate are two brands I can name off the top of my head. Most kits include a Bosch sensor. For most kits with a gauge, the gauge is also the controller. Kits with controllers but without gauges do exist. Many kits will include weld-in bungs if your exhaust needs somewhere for the sensor to install. OBD2-interfacing gauges exist and will be clarified below.

1. Physical Install
The sensor will need to be screwed into a bung in the exhaust. If you have a free bung, great. If you have to add one, see your wideband's manual for advice regarding placement. Options do exist to replace a narrowband with a wideband and send a simulated output, and will be clarified below. You will also need a mounting solution for the controller/gauge. Shameless plug, I designed and 3d printed a gauge pod for the stock Cobalt boost gauge, an Innovate MTX wideband, and the Cobalt ambient light sensor. Info here.

2. Electrical Install
You will need to get 12v power and ground to the controller, at a minimum. Wherever you're grabbing power from, whether via relay from the battery or other source, it should be a key-on power source. Leaving it powered all the time will kill your battery, and forgetting to power it on with the car will kill the sensor as it has a heater that needs to be powered so it doesn't get coated with crud. Most gauges will also have an additional signal wire that, when tapped into a circuit that's powered with the headlights, will dim the gauge with the headlights on (aka when it's dark).

I honestly don't remember where I pulled my switched power source from. I think it was from the circuit in the front I had planned for my heat exchanger power source as I ended up installing that in the back of the car. I just used a T-tap on a headlight wire planning to come back to it... you can guess how that worked out.

3. Bringing in Output Data
So you've got your sensor in the exhaust, your gauge/controller powered and mounted, and you're looking at some numbers. Now what? You're probably going to want to use this data when tuning in HP Tuners. There are 4 ways to get it there (off the top of my head):
  1. Connect your gauge/controller straight to your logging/tuning computer. I've done this once before, it was a pain. It involved a serial -> USB adapter, and I spent more time trying to get that set up and running than it did to create a base tune in HP Tuners.
  2. Purchase an HP Tuners Pro interface module with 0-5v inputs on the side. Wire your 0-5v output from the gauge/controller into the interface module. The HP Tuners channel will simply be the MPVI or MPVI2 Pro input.
  3. My favorite option, wire the 0-5v output into the AC pressure sensor signal wire. On my setup, the yellow wire coming off the gauge is the 0-5v analog output. When thinning the engine harness, I removed everything for the AC compressor clutch relay, and the 5 volt and low reference for the AC refrigerant pressure sensor. I kept the red/black wire on the engine side of the engine harness and connected the two together. If you don't have an '06 LSJ (like a loser) then your wire color may vary. Then, I take my butt over to HP Tuners, add the AC Pressure Sensor channel and Commanded AFR to my logs, set up Math Parameters for Wideband AFR and AFR error (and gripe about HP Tuners wanting to do AFR in gasoline numbers instead of Lambda).
  4. OBD2 Wideband... although this only works with a CAN PCM, which I think includes the LNF and LAP, does not include LSJ or early L61, and which may or may not include LE5 and late L61? Piece of cake, plug it into the OBD2 port, plug your HP Tuners interface into the OBD2 port, configure it I don't know how because I don't have it, done.
  5. Write down your AFR under WOT and then compare it to your commanded AFR in HP Tuners and then adjust your tune. Spare motors suggested for this method.
Final thoughts: as I've mentioned elsewhere before, in my worthless opinion, the only downside to my favorite method of getting data into HP Tuners via the AC pressure signal wire is the effort it takes to hook up the first time. Wiring into the HP Tuners interface is certainly easier, but then you have to either leave it in the car or disconnect the signal wire and tape it up to protect it from shorting.

TL;DR If you want or need to add a wideband O2 sensor, buy an OBD2 wideband if you have an LNF or LAP, HP Tuners Pro interface if you want to spend 5 minutes hooking it up, or go through the AC if you want a clean, reliable, permanent solution.


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Well-Known Member
To add to 3.4., all you have to do in HPTuners is repoll parameters and add the wideband. See here:

Just did it for my 2.2 LAP and it couldn't have been easier.


Goblin Guru
To add to 3.4., all you have to do in HPTuners is repoll parameters and add the wideband. See here:

Just did it for my 2.2 LAP and it couldn't have been easier.
Nice. I was pretty sure this worked for an LNF but wasn't sure about an LAP. Still not sure if it works on any or all LE5 or L61. I am confident this doesn't work on an LSJ though. Will add those comments into the original writeup.


Well-Known Member
This is super helpful and I'm right in the middle of my wideband install now. Does anybody have the connection diagram to the ECM for an LAP motor? 09-10 2.2. I thinned the wires out of my harness.


Well-Known Member
I just completed option 3 today on my LAP. Couple notes.

My radiator fan turned on right away. Have to change ac pressure vs fan map in the calibration. Set all to zero so the wideband won't turn the fan on.

I'm using the Autometer wideband where 0 volts is 10.0 and 4 volts is 17.0 AFR. Calculation is ([7101.10]*1.75)+10

Otherwise, this worked great and is super cool. This post was perfect timing.


Well-Known Member
Yeah I had no problems with it. I'm running my gauge right where the cobalt gauge cluster should be