There’s nothing that kills the thrill of a trail ride faster than a flashing check engine light. Your powerful Polaris 850 suddenly feels sluggish, goes into limp mode, and the dash flashes a dreaded three-letter code: DET. Your heart sinks, and the questions start racing. What does it mean? Is my engine toast? How much is this going to cost me?
Take a deep breath. While this code is serious, it’s often caused by something surprisingly simple. You don’t have to immediately load it onto the trailer for a trip to the dealer. We promise this guide will give you the expert insights you need to solve the problem yourself.
In this complete guide, we’ll break down exactly what the 2020 Polaris 850 DET code means, walk you through the most common culprits from bad fuel to simple sensor checks, and provide a clear, step-by-step action plan. You’ll learn how to diagnose the issue and get your rig running strong again, often with just a few basic tools and a little bit of garage time.
What “DET” Code Means and Why You Can’t Ignore It
First things first, let’s get the technical definition out of the way. “DET” stands for detonation. In simple terms, this is an uncontrolled explosion of the air/fuel mixture inside your engine’s cylinder, rather than a smooth, controlled burn.
Think of it like this: a proper combustion event is a strong, steady push on the piston. Detonation is like hitting the top of that piston with a sledgehammer. It’s violent, creates immense heat and pressure spikes, and is incredibly destructive to internal engine components like pistons, rings, and connecting rods.
Your Polaris is smart. It has a sophisticated sensor, called a knock sensor, that “listens” for the tell-tale signs of this destructive event. When it detects detonation, it immediately triggers the DET code and puts the engine into a reduced-power “limp mode” to prevent catastrophic failure. Ignoring it is not an option; you’re risking a complete engine rebuild.
The Number One Culprit: All About Your Fuel
Before you start tearing into wiring or ordering sensors, you need to look at the most common cause of the 2020 Polaris 850 DET code: the fuel in your tank. Over 80% of the time, the issue lies here. This is one of the most common problems with the 2020 Polaris 850 DET code, but also the easiest to fix.
Low Octane Blues: The Most Common Mistake
The Polaris 850 Patriot engine is a high-performance, high-compression powerhouse. It’s designed specifically to run on premium, high-octane fuel—that means 91 octane or higher. Using lower octane fuel, like regular 87, is the quickest way to trigger a DET code.
Lower octane fuel is less stable under compression and ignites too early, causing that engine-killing knock. Always, always fill up with 91+ octane from a busy, reputable gas station to ensure you’re getting fresh, quality fuel.
Stale Fuel and Water Contamination
Did your machine sit for a few months over the winter? The fuel in the tank has likely gone bad. Modern gasoline, especially with ethanol, can absorb water from the atmosphere. This leads to “phase separation,” where a layer of water and ethanol sinks to the bottom of your tank and gets sucked into the fuel pump.
This water-logged fuel doesn’t combust properly and is a guaranteed recipe for detonation. One of the best practices for your machine is to use a quality fuel stabilizer if you know it’s going to be parked for more than 30 days.
Your First Action Step: The Fuel System Reset
If you suspect bad or low-octane fuel, here’s how to 2020 Polaris 850 DET code fix it:
- Drain the Old Fuel: Safely siphon or drain all the old fuel from the tank. Be sure to do this in a well-ventilated area away from any ignition sources.
- Add Fresh, High-Octane Fuel: Refill the tank with at least a couple of gallons of fresh 91+ octane premium gasoline.
- Add Injector Cleaner: This is a great time to pour in a bottle of a quality fuel system cleaner, like Sea Foam or Lucas Fuel Treatment, to help clear out any gunk from the old fuel.
- Cycle the Key: Turn the key to the “on” position (without starting the engine) a few times. You should hear the fuel pump prime. This pushes the fresh fuel through the lines and injectors.
- Clear the Code & Test: Start the engine and let it run for a few minutes. In many cases, the code will clear itself after the engine computer recognizes conditions are back to normal.
Beyond Fuel: A Step-by-Step 2020 Polaris 850 DET Code Guide
If a fresh tank of premium fuel didn’t solve the problem, it’s time to grab some tools and dig a little deeper. Follow this diagnostic guide in order, moving from the simplest checks to the more involved ones.
Step 1: Inspect Your Spark Plugs
Your spark plugs are a window into the health of your engine. A fouled or incorrect spark plug can be a direct cause of detonation. You’ll need a spark plug socket and a ratchet.
Pull the plugs and examine the tips. A white, blistered appearance indicates the engine is running dangerously hot or lean. Black, sooty deposits show it’s running rich. Oily fouling can indicate other issues. Regardless, if they look worn, it’s cheap insurance to replace them with the OEM-specified NGK spark plugs, gapped to the correct spec found in your owner’s manual.
Step 2: Check the Knock Sensor and Wiring
The knock sensor is the very part that triggers the code. While the sensor itself rarely fails, its wiring is vulnerable to damage. Locate the knock sensor on the engine cylinder (consult your service manual for the exact location).
Carefully inspect the wiring leading to it. Look for any signs of rubbing, fraying, melting, or rodent damage. Unplug the connector and check for corrosion or moisture inside. A poor connection can send a bad signal to the ECU, falsely triggering the DET code.
Step 3: Look for Air Leaks (Lean Condition)
A lean air/fuel mixture (too much air, not enough fuel) raises combustion temperatures and is a prime cause of detonation. This is often caused by a vacuum leak somewhere after the throttle bodies.
The most common culprits are the rubber intake boots that connect the throttle bodies to the engine. Over time, they can dry out and crack. With the engine off, carefully inspect them for any visible cracks or splits. Gently wiggle them to see if they are loose on their mounts.
Step 4: Consider Your Cooling System
An overheating engine is an engine that’s prone to detonation. Heat is the enemy. Your troubleshooting should include a quick check of the cooling system.
Is your coolant level full? Are your radiator fins clear of mud and debris? When the machine gets up to temperature, does the cooling fan kick on as it should? A simple issue here can lead to the dreaded DET code.
Advanced Troubleshooting: When the Simple Fixes Don’t Work
If you’ve gone through the steps above and are still staring at a DET code, the issue may be more complex. This is where this 2020 Polaris 850 DET code care guide moves into more advanced territory. Proceed if you are a confident DIY mechanic.
Testing Fuel Pressure
A weak fuel pump or a clogged fuel filter can’t deliver the volume of fuel the engine needs under load, creating a lean condition. You’ll need a fuel pressure test gauge to properly diagnose this. If the pressure is below the factory specification, your fuel pump may be on its way out.
Carbon Buildup Concerns
Over time, carbon deposits can build up on the piston crown and in the combustion chamber. These deposits can glow red hot, acting like rogue spark plugs and pre-igniting the fuel mixture. This is another area where adopting a sustainable 2020 Polaris 850 DET code approach by keeping your engine clean pays off in performance and longevity.
Running a high-quality top-end cleaner through the system periodically can help break down these deposits and prevent future issues.
Knowing When to Call a Pro
There’s no shame in knowing your limits. If you’ve checked the fuel, plugs, and wiring and still have the code, it’s time to see a qualified technician. They have advanced diagnostic tools that can read live sensor data, test injector pulse width, and pinpoint the problem quickly, saving you time and frustration.
Best Practices for Preventing the DET Code for Good
The best way to fix a problem is to prevent it from ever happening. The benefits of 2020 Polaris 850 DET code prevention are clear: more ride time and less wrench time. Follow these best practices:
- Always Use Premium Fuel: We can’t stress this enough. Use 91 octane or higher from a top-tier gas station.
- Use Fuel Stabilizer: If your machine is going to sit for more than a month, treat the fuel with a quality stabilizer.
- Follow Maintenance Intervals: Change your spark plugs according to the schedule in your owner’s manual, not just when there’s a problem.
- Perform Regular Inspections: Before each ride, do a quick visual check of your intake boots, coolant level, and visible wiring harnesses.
- Keep it Clean: A clean machine is easier to inspect and a clean radiator works more efficiently. This is an easy, eco-friendly 2020 Polaris 850 DET code tip that keeps your engine happy.
Frequently Asked Questions About the 2020 Polaris 850 DET Code
Can I just clear the code and keep riding?
No. The DET code is your engine’s cry for help. The limp mode is active to prevent catastrophic damage. Clearing the code without fixing the underlying issue—be it bad fuel, a fouled plug, or a lean condition—is asking for a massive repair bill down the road.
What specific error codes are related to DET?
The “DET” warning on your dash is often accompanied by a specific fault code you can read with a diagnostic tool. The most common are 65590, 65591, and 65592, which correspond to knock detection on specific cylinders or a general knock condition. These help narrow down the problem.
Will a performance tune or aftermarket exhaust cause the DET code?
It can, if not done correctly. An aftermarket exhaust that changes backpressure or a “canned” tune that isn’t optimized for your specific machine and elevation can lean out the air/fuel mixture and cause detonation. Always use reputable tuners who adjust fuel maps properly.
Tackling a 2020 Polaris 850 DET code can feel daunting, but as you’ve seen, the solution is often straightforward. By starting with the most likely culprit—your fuel—and working through the system methodically, you can diagnose and fix the issue yourself. Stay diligent with your maintenance, feed your machine the high-octane fuel it craves, and you’ll spend more time kicking up dirt and less time staring at warning lights.
Now get back in the garage, use this guide, and get that 850 ready for the next adventure. Ride hard and ride safe!
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