Polaris Sportsman 850 Code 45 - Your Ultimate DIY Diagnostic & Repair

You’re geared up. The trail is calling. You turn the key on your Polaris Sportsman 850, ready for an adventure, and then you see it—the dreaded check engine light, followed by fault code 45 on your display. Suddenly, your plans for mud and glory are on hold, replaced by the frustration of a cryptic error.

We’ve all been there. That sinking feeling can derail a whole weekend. But what if that code wasn’t a trip-ender, but just a small bump in the road you could fix yourself?

Promise yourself this: you can tackle this. This comprehensive guide is here to demystify the polaris sportsman 850 code 45, walk you through exactly what causes it, and give you the step-by-step instructions to diagnose and fix it right in your own garage. We’ll cover the tools you need, the parts to check, and the pro tips to get you back on the trail fast.

What Exactly is a Polaris Sportsman 850 Code 45?

Before we grab any tools, let’s understand what your machine is trying to tell you. Modern ATVs like your Sportsman use an Engine Control Unit (ECU) to monitor dozens of sensors. When a sensor’s reading is outside its normal range, the ECU logs a Diagnostic Trouble Code (DTC) to alert you.

Code 45 specifically points to a problem with the Barometric Air Pressure (BAP) sensor circuit. This isn’t just a random part; it’s crucial for performance.

The BAP sensor’s job is to measure the atmospheric pressure of the air around you. It sends this information to the ECU, which then adjusts the air-fuel mixture for optimal combustion. This is especially important as you change elevation—air is less dense at the top of a mountain than it is at sea level.

When this sensor or its circuit fails, the ECU is essentially flying blind, leading to a host of noticeable symptoms:

Poor or Hard Starting: The engine struggles to fire up because the fuel mixture is wrong.
Rough Idle: The engine may sputter or idle unevenly.
Significant Loss of Power: You’ll feel a lack of “get up and go,” especially under acceleration.
Bad Fuel Economy: The engine will likely run rich (too much fuel), burning through your tank faster.
Black Smoke from Exhaust: This is a classic sign of an overly rich fuel mixture.

The Most Common Problems Causing Code 45

While the code points to the BAP sensor circuit, the problem isn’t always the sensor itself. In our experience at the shop, wiring issues are just as common, especially on a machine that sees mud, water, and vibration. This section of our polaris sportsman 850 code 45 guide breaks down the likely culprits.

The BAP Sensor Itself Has Failed

Like any electronic component, the BAP sensor can simply wear out and fail over time. Internal components can break down, leading to incorrect or no voltage signals being sent to the ECU. This is a straightforward failure that requires a replacement part.

Wiring and Connector Issues

This is one of the most frequent common problems with polaris sportsman 850 code 45. The wiring harness on an ATV lives a hard life. Here’s what to look for:

Corrosion: Water and mud get into connectors, causing the pins to corrode (often turning green). This creates resistance and blocks the electrical signal.
Damaged Wires: A wire can get chafed against the frame, pinched by a component, or even chewed by a rodent, causing a short or a complete break.
Loose Pins: The metal pins inside the plastic connector can become loose or pushed back, creating a poor connection that comes and goes with vibration.

ECU (Engine Control Unit) Faults

This is the least likely scenario, but it’s worth mentioning. In very rare cases, the problem can be internal to the ECU itself. Always exhaust every other possibility before suspecting the ECU, as it’s an expensive and complex part to replace.

Tools and Parts You’ll Need for the Job

The great news is that you don’t need a full professional workshop to diagnose this code. Having the right tools on hand makes the job much smoother. Here’s your checklist:

Basic Socket Set: A small metric socket set (8mm, 10mm, etc.) will handle most fasteners.
Digital Multimeter (DMM): This is your most important diagnostic tool. You don’t need a fancy one, just a basic model that can read DC Volts and Ohms (resistance).
Electronic Contact Cleaner: A spray cleaner specifically designed for electrical connections. Do not use brake cleaner or carb cleaner!
Dielectric Grease: This non-conductive grease protects electrical connections from moisture and corrosion after you’re done.
A Good Flashlight or Headlamp: You’ll be looking in tight, dark spaces.
Shop Rags and Gloves: To keep things clean and protect your hands.

If your diagnosis points to a failed part, you may need a new BAP sensor. It’s best to get the part number directly off your old sensor or call a dealer with your VIN to ensure you get the correct one.

How to Polaris Sportsman 850 Code 45: A Step-by-Step Fix

Alright, let’s get our hands dirty. Follow these steps methodically. Don’t skip ahead! The goal is to find the problem, not just throw parts at it. This is one of the key polaris sportsman 850 code 45 best practices.

Step 1: Safety First & Initial Inspection

Before you do anything, make sure your ATV is parked on level ground and the engine is cool. Turn the key to the OFF position and, for good measure, disconnect the negative terminal on your battery to prevent any accidental shorts.

Now, do a quick visual inspection of the engine bay. Look for anything that seems out of place—unplugged connectors, wires hanging loose, or signs of rodent nests.

Step 2: Locate the BAP Sensor

On most Polaris Sportsman 850 models, the BAP sensor is a small, black plastic sensor located on the airbox or very close to the throttle body. It will have a 3-wire electrical connector plugged into it. It’s often held in place by a single small bolt or screw.

Step 3: Inspect the Connector and Wiring

This is where most problems are found. Carefully unplug the electrical connector from the BAP sensor. You may need to press a small tab to release it.

Shine your flashlight inside both the sensor side and the harness side of the connector. Look for any signs of green or white corrosion, dirt, mud, or moisture. Check that the small metal pins are straight and not pushed back into the housing. If you see any corrosion, spray it liberally with your electronic contact cleaner and use a small brush (like a toothbrush) to gently scrub it clean. Let it air dry completely.

Step 4: Test the Circuit with a Multimeter

Here’s where your DMM proves its worth. With the key ON (engine OFF) and the sensor still unplugged, we’ll test the wires on the harness side of the connector.

Check for 5V Reference: Set your DMM to DC Volts. Place the black probe on a good ground (the negative battery terminal or a clean spot on the frame). Probe each of the three terminals in the connector with the red probe. One of them should read approximately 5 volts. This is the reference voltage from the ECU. If you don’t have 5V, you likely have a wiring problem between the ECU and the sensor.
Check for Ground: One of the other wires should be the ground. Keep the red probe on the positive battery terminal and probe the remaining two wires with the black probe. One should show battery voltage (around 12V), confirming it’s a good ground path.
Check the Signal Wire: The remaining wire is the signal wire that sends the pressure reading back to the ECU. The main issue here is to check for breaks. You can do this by checking for continuity between the connector and the corresponding pin at the ECU, but that’s a more advanced step.

If your reference voltage or ground is missing, you need to trace that wire back to find the break or short. If both are present, the sensor itself is the next suspect.

Step 5: Replacing the BAP Sensor

If you’ve confirmed the wiring has power and ground, and the connector is clean, the sensor itself is the most likely culprit. Replacement is typically very simple. It’s usually held on by one or two small bolts. Remove them, gently pull the old sensor out, and install the new one. Be sure to transfer any o-rings if necessary.

Step 6: Final Steps and Clearing the Code

Before you plug in the new sensor, apply a small amount of dielectric grease to the connector terminals. This will help seal out moisture and prevent future corrosion.

Plug the connector in firmly until it clicks. Reconnect your battery. Now, turn the key on. On most models, the code will clear itself after the ECU receives a good signal from the new sensor on startup. Start the engine and let it run for a minute. The check engine light should go out.

Best Practices for Preventing Future Fault Codes

Fixing the problem is great, but preventing it is even better. Adopting a few habits into your polaris sportsman 850 code 45 care guide can save you headaches down the road.

Periodically check and clean your main electrical connections, especially after a particularly wet or muddy ride. A little preventative maintenance goes a long way.

When you’re washing your machine, try to avoid spraying high-pressure water directly at sensors and connectors. And always use dielectric grease on any connection you have apart—it’s cheap insurance against corrosion.

Thinking about a sustainable polaris sportsman 850 code 45 approach means not just fixing the problem, but doing it smartly. Properly diagnosing the issue prevents you from throwing away a perfectly good sensor, which reduces waste. Choosing high-quality replacement parts ensures longevity, meaning fewer replacements over the life of your ATV. This is the most eco-friendly polaris sportsman 850 code 45 mindset you can have.

Frequently Asked Questions About Polaris Sportsman 850 Code 45

Can I still ride my Sportsman 850 with code 45?

It’s not recommended. While the machine might run, it will perform poorly, use excessive fuel, and run rich. A rich condition over a long period can foul spark plugs and potentially damage your catalytic converter, leading to a much more expensive repair.

How much does it cost to fix code 45?

One of the biggest benefits of polaris sportsman 850 code 45 DIY repair is the cost savings. If it’s a simple corroded connection, the fix costs you nothing but time and a bit of contact cleaner. If you need a new BAP sensor, the part itself typically costs between $50 and $100. A repair shop could charge anywhere from $200 to $400, mostly in diagnostic labor.

The code came back after I replaced the sensor. What now?

If a new sensor didn’t fix it, the problem is almost certainly in the wiring. Go back and re-check for 5V reference and ground at the connector. The issue could be an intermittent break in a wire that only appears when the harness is moved. Carefully inspect the entire length of the harness from the sensor to the ECU.

Tackling a check engine light can feel intimidating, but code 45 is one of the most straightforward issues to diagnose on your Sportsman 850. By following these steps, you’ve not only learned how to fix this specific problem but have also gained valuable diagnostic skills.

You have the knowledge and the plan. Now you can confidently grab your tools, solve the problem, and get your Polaris back on the trail where it belongs. Ride safe and have fun out there!

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Thomas Corle

Founder & Automobile expert at FatBoysOffroad

Automobile expert and off-road enthusiast, sharing in-depth knowledge of vehicles, gear, and adventures. Helping readers make smart decisions and enjoy the thrill of off-roading safely and confidently.