Harley Davidson Oxygen Sensors: The Complete Guide for Exhaust Upgrades & Tuning

Harley Davidson Oxygen Sensors: The Complete Guide for Exhaust Upgrades & Tuning

For Harley-Davidson owners, the Oxygen Sensor (O2 Sensor) is often the most misunderstood part of the bike.
You might ignore it until you install a new set of Vance & Hines or Cobra exhaust pipes. Suddenly, your bike is popping on deceleration, running too hot, or idling roughly.

Whether you are riding a Softail, Dyna, Touring, or Sportster, the O2 sensors are the critical link between your engine and your bike's computer (ECM).

At Automotive-leader, we supply high-precision replacement sensors that keep your V-Twin running at peak performance. In this guide, we’ll explain how they work, why they fail, and which part numbers (like the common 32700005 & 32700006) you actually need.

1. Why Does My Harley Need O2 Sensors?

In the past, Harleys used carburetors. Today, they use Electronic Fuel Injection (EFI).
The O2 sensors measure the amount of oxygen in the exhaust gas. They tell the ECM whether the engine is running Rich (too much fuel) or Lean (not enough fuel).

  • Closed Loop: Cruising speed. The ECM uses O2 sensor data to adjust fuel for MPG and smooth running.

  • Open Loop: Full throttle. The ECM ignores the sensors and dumps fuel for power.

The "Tuning" Problem:
If you change your exhaust pipes or air cleaner (Stage 1 Upgrade) without updating your sensors or tuning, your bike will run dangerously lean (hot), potentially damaging the engine.

2. Signs of a Bad (or Lazy) Harley O2 Sensor

Unlike cars, a bad sensor on a Harley affects the "feel" of the ride instantly.

  1. Decel Pop / Backfiring: Loud popping noises when you let off the throttle.

  2. Surging Idle: The bike can't hold a steady RPM at traffic lights.

  3. Engine Heat: A failing sensor can cause the engine to run lean, making the pipes glow red hot.

  4. Poor MPG: You are filling up the tank more often than your riding buddies.

  5. Historic Codes: You might see codes like P0131 (Front Lean) or P0151 (Rear Lean).

Think it might be just dirty?
Sometimes, carbon buildup is the issue.
👉 [Read More: How to Clean O2 Sensor: A Comprehensive Step-by-Step Guide] 

3. The Great Debate: 18mm vs. 12mm Sensors

Harley changed their sensor technology around 2010-2012. Knowing the difference is vital to buying the right part.

  • Older Models (Pre-2011): Used larger 18mm sensors. These are usually "Unheated" (1-wire or 2-wire). They take longer to warm up.

  • Newer Models (2012+): Switched to smaller 12mm Heated sensors (4-wire). These are much faster and more accurate.

Why does this matter?
If you buy aftermarket exhaust pipes, you must ensure the "O2 Bungs" (the holes for the sensors) match your sensor size (12mm or 18mm).

4. Front vs. Rear: They Are NOT the Same!

This is the #1 mistake Harley owners make.
A V-Twin engine has two cylinders: Front and Rear.

  • Front Sensor: Usually has a longer cable to reach the connector.

  • Rear Sensor: Usually has a shorter cable.

  • Color Coding: Harley often uses Black connectors for Rear and Gray for Front to help you distinguish them.

Always check the cable length before ordering!

5. Find Your Part Number (Cheat Sheet)

We stock the high-performance replacements for the most common Harley applications. Here is how to match them up.

For 2012-2017 Softail / Dyna / V-Rod

These bikes use the modern 4-wire heated sensors.

  • Front Sensor (Gray Plug): Replaces OEM 32700006

  • Rear Sensor (Black Plug): Replaces OEM 32700005

  • Fits: Fat Bob, Street Bob, Wide Glide, Softail Slim, etc.

👉 [Buy Now: 2Pcs Harley Dyna Softail Oxygen Sensors (Front & Rear) - 32700005/6] 

For Touring Models (Road King, Street Glide)

Touring bikes often have different wire lengths due to the exhaust routing.

  • Replaces OEM: 27729-10 (and related variants)

👉 [Shop Harley Touring Oxygen Sensors] 

6. Installation Tips for Bikers

Changing these sensors is a quick garage job, but requires special care.

  1. Special Socket: You need an "O2 Sensor Socket" with a slit cut out for the wire.

  2. Anti-Seize: Be very careful not to get anti-seize grease on the sensor tip! This will kill the sensor instantly.

  3. Cable Routing: Use zip ties to keep the sensor wires away from the hot engine block. Melted wires are a common cause of failure.

Need a generic installation guide?
👉 [Read More: How to Install Oxygen Sensor: A Step-by-Step DIY Guide] 

7. Conclusion

Your Harley is a precision machine. Don't let a $50 sensor ruin the performance of your $2,000 exhaust system upgrade.
At Automotive-leader, our sensors are built to handle the vibration and heat of a V-Twin engine.

Ready to ride?
Select your model below and get back on the road.

👉 [Shop All Motorcycle Sensors]