Updated: Jun 18
Accurate data from a Wide-Band Oxygen Sensor is crucial to successfully tuning a vehicle.
Even with a good AEM X-Series UEGO, converting from an analog 0-5v signal to an air fuel ratio that you can understand may be an obstacle. Some don't have the proper equipment to natively log an analog input (HPTuners Pro Link), and others fight with ground / voltage offset issues while trying to read the UEGO through a pin on the factory ECU.
This guide will help demonstrate how to use the Serial output on the X-Series UEGO in order to get a digital reading into HPTuners, without Pro Link or any extra math.
Analog Communication (The Problem)
Traditionally, gauges output an analog voltage to represent an air fuel ratio. For example, the 30-0300 would output 3.11 volts. We would then have to configure HPTuners to multiply 3.11 * 2.375, and add an offset of 7.31 to find that the gauge is reading: (2.375*3.11)+7.31 = 14.69 AFR This math is convoluted by the fact that a weak ground, or wiring problem, can skew the formula. Any time we use a customer installed wide-band, we recalculate this formula, and often find that the default equation is more than 10% off. The predecessors of the X series do not have a dedicated ground for their analog outputs, dropping accuracy further.
Serial Communication (Our solution)
The AEM 30-0300 has several different output options, making it one of our preferred gauges to work with. The output we are utilizing in this guide is called a "Serial" output.
The Serial output can communicate with your computer's Universal Serial Bus (USB), and digitally output a reading of "14.69" rather than a voltage that needs manipulated into data. HPTuners, even without Pro Link, is able to listen to your computer's communications ports, for data that looks like a Wide-Band reading. This is the easiest way to bring accurate Wide-Band data into your vehicle's data logs.
On To The Build!
Above, you can see a schematic of the modifications we're intending to make. The Vehicle Interface cable coming out of the X-Series has several wires that enable the different functionalities of the gauge. We are going to extend the power (Red) and ground (Black) wires to a 12v Cigarette Lighter Adapter for ease of use, and we will extend the Serial Data (Blue) output from the X-Series to a location near the 12v outlet for easy logging.
You may have your own preferences of components to make the connections and coverings, and I encourage you to work with the components you are most comfortable with. I will be using solder joints, shrink tube, and woven split loom. These techniques give me the best fit and finish for a piece of electronics that will live inside of the car.
Wideband that supports Serial Output I am using the AEM X-Series 30-0300. It's a good (the best?), reliable gauge, and is versatile in that it has many outputs, and can be easily configured to read Lambda (Which you should learn to use). If you have a 2008+ vehicle, there are easier options that we will cover in another post. Link to X-Series on our Storefront
12v Vehicle Outlet Adapters For this project, I picked an adapter from CUZEC. It has a built-in fuse, an LED indicating that the adapter is getting power, and firm side-connections to ensure it does not come loose while driving the vehicle. Amazon Link
Shrink Tube Shrink Tube is my favorite way of insulating and cleaning up wiring projects. An assortment of 2:1 shrink tube is a great thing to have on hand when undertaking a wiring project. Just remember to slip it over the wire before you make a solder point :) Amazon Link
DB9 Female Serial Cable Serial Data Lines typically use a standard "D" shape Female Block connector with 9 Pins. The standard for this is "DB9". We will be using this cable to adapt our Blue serial line and our Black ground line into a common connector we can use. These DB9 serial cables commonly have a headphone jack on one end, as they're use to configure TVs and other appliances. Amazon Link
Serial to USB Converter This cable plugs into the DB9 cable we are adding to our Wide-Band, and works to control traffic between your computer and the gauge. This will be the component that plugs into your USB port after modification is complete. From my years working as a Systems Engineer, I have had favorable results from StarTech brand cables Amazon Link
16 Gauge Automotive Wire For the insignificant amount of amperage used by this project, 16 gauge wiring will be a good fit respective to voltage drop and wire size. It's a good idea to look for automotive specific wiring, as the properties of the outer sheathing are intended to prevent degradation if they come in contact with your vehicle's fluids and heat. Amazon Link
Split Wire Loom While not functionally required, self closing split loom cleans up and protects the lengths of wires we are going to assemble in this project. 1/4" self closing loom is a good size for this project, and works well for enclosing 2-3 wires. Amazon Link
We're going to start by cutting some of our 16-gauge automotive wire to lengths that are appropriate for this project:
- 5' Red (For Power)
- 5' Blue (For Serial Data) - 4'1" Black (For Ground) - 1'1" Black (For Serial Data)
- 1'1" Black (To 12v outlet)
I've left an extra 1" on the black wires, as some of the wire length will be lost when the grounds are stripped and soldered in order to "T" off towards the Serial Data line.
With our new wires cut to length, we can move onto preparing the AEM's harness, so that we can solder onto it. The leads on the AEM harness come pre-soldered, which (while convenient) does not lend to a reliable solder joint. We are going to cut the pre-soldered sections off of the leads:
Next, we will be soldering our Black Red and Blue wires onto this harness. We will start with the Red power wire, and I will walk you through a reliable method of joining these wires with a solder joint. Strip roughly 3/4" off of the AEM's red lead, as well as our new long Red wire.
To start our solder joint, fan out the strands of both wires.
Thread the fanned strands into each other, holding the wires facing each other at a ~90* angle.
Grab all of the strands from the AEM and twist them together clockwise, while holding the copper strands from the new Red wire, twisting them together counter-clockwise.
Roll the twisted up bundles of strands opposite directions around the un-twisted sections of the opposing wires. The AEM section will twist towards us and around the bottom of the wire, while the new section will twist away from us and around
The desired result looks as follows, and is ready to be soldered. By weaving the wires together link this, we have created a strong mechanical connection that will hold several pounds of force before unraveling -- Even before soldering the wires together.
Next, solder the long new Blue and Black wires to their respective partners on the AEM harness with this technique, and cover them with Shrink Tube to isolate them from each other.
I recommend using self-closing split loom to bundle all of these wires together, and tidy up the project. Use the ~4" length of new black wire to help you judge the length of split loom you would like to use. Remember we will need to solder onto the far end of the black wire, so I suggest around 2-3" of stick-out on the black wire after looming. My loom ended up being ~4'6" long. I use shrink tube at the ends of the split-loom to keep it from unraveling.
Next, we're going to solder and complete the ground junction point at the opposite side of the new wiring harness. It would be wise to think through how you may want to use shrink tube to bundle wires together. Below is a picture of my finished junction point that may help you plan for this step.
Before starting on this junction, I slipped a medium sized piece of shrink tube over all three (Blue Black and Red) wires from the main harness.
Next, Strip one end of each of the smaller ground wires, along with the end of the new ground coming out of the AEM main harness.
Using the same techniques as before, we're going to thread and twist the wires together. One of the short black wires should point back towards the gauge, and the other short wire should be opposing it towards the 12v power source.
The result should look as follows:
The wires can now be soldered and covered with shrink tube. Now is a good time to route and support each group of wires with shrink tube as illustrated earlier.
Next, we will modify and solder the 12v outlet adapter to the Black and Red wires. Cut the supplied connectors off of the adapter, and then trim the AEM's new power and ground leads so that they are equal length to each other.
Strip the ends of the power and ground wires to be soldered, and remember to put Shrink Tube over the wires before soldering them together. I added an extra medium sized shrink tube over both wires, to allow me to bundle them together over top of both solder joints.
If you intend to use shrink-tube and woven split loom over this length of cable, it would be wise to add two additional large piece of shrink tube to the 12v adapter now.
With the 12v adapter soldered on, we will move onto modifying the DB9 Serial Cable. Cut the 3.5mm headphone jack off of the end of the connector, and strip off the outer sheathing with one of the larger openings of your wire stripper. You don't want to damage the tiny wires inside.
Conventionally speaking, the bare wire wrapped around the aluminum shielding will be your ground wire. The Yellow wire should be your computer's receive wire (AEM's transmit wire). The Blue wire should be your computer's transmit wire (Which we will not use).
If you are using the cable that I have suggested, you can trust these colors. Other brands may not use the same convention. If you do not have the same cable, the computer's receive wire (the one we want) will have continuity to Pin 2 (Second from the left on the top row) on the DB9 connector. You can identify this wire by measuring resistance from Pin 2 to each wire with a multimeter.
We can cut the Blue wire off of the DB9 serial cable, as it is not used in this application. Since the ground is exposed, it would be wise to cover the cut end with liquid electrical tape or hot glue to avoid a short to ground.
Strip the yellow wire, as well as the remaining Blue and Black wires coming from the new AEM harness. I recommend stripping 1 1/4" from the yellow wire to allow extra surface area for a good solder joint.
With excessively small wires such as this, it's easy to accidentally break off some of the conductors. Use caution to keep all of the strands intact, or be prepared to cut this end off of the DB9 cable to try again.
If you intend to use shrink-tube and woven split loom over this length of cable, it would be wise to add an additional large piece of shrink tube to the DB9 cable now.
Solder the exposed ground wire to the Black wire coming from the AEM, and solder the Yellow wire to the Blue wire coming from the AEM. Remember to put shrink tube over the blue and black wires before soldering. I added two sections of large shrink tube over both wires as well, so that I could add extra rigidity to the joint.
Use loom and shrink tube to finalize a professional looking Serial to USB wide-band. The StarTech serial to USB converter will plug into the end of the DB9 cable, and into your USB port.
In HP Tuners, you can add the AEM to your channels by selecting AEM - AFR under the Serial Port External Inputs section.
In order to log data, the AEM needs to be powered on and talking over the Serial port before you click on the "Connect to Vehicle" button. If the AEM - AFR channel disappears when you begin to Record Data, that indicates that HPTuners did not see any AFR data over the serial port during the connection process. To resolve this, disconnect and reconnect to the Vehicle with the buttons in HP Tuners VCM Scanner.
We can now log accurate data from our Wide-Band Oxygen Sensor to HP Tuners without the Pro Feature set, and we can easily move our installation from vehicle to vehicle. The assembled cable is one of several we loan out with deposit for Remote Tuning. We can also make and further customize these gauges for you. Please reach out if you have any questions, or if you would like us to make you a gauge. As an Amazon Associate, I earn a small percentage of qualifying purchases. We appreciate your support so that we can continue delivering instructional content like this.