Polaris Rzr Code 65590 And 65591 - Your Complete Misfire Diagnostic

There’s nothing worse. You’re geared up, miles from the trailhead, and just as you’re about to conquer that perfect mud hole, your RZR sputters. The check engine light flashes on, and the dash screams an error code at you. Your rig goes into limp mode, and your epic ride grinds to a halt. We’ve all been there, and it’s beyond frustrating.

If you’re staring at your dash seeing a polaris rzr code 65590 and 65591, you’ve come to the right place. Don’t call for a tow just yet. We promise to demystify these common misfire codes and give you a clear, step-by-step roadmap to diagnose and fix the problem yourself.

In this guide, we’ll break down exactly what these codes mean, walk you through the most common causes—from simple fixes to more complex issues—and give you the pro tips you need to get your machine roaring back to life. Let’s get those wrenches turning and get you back on the trail.

What Do Polaris RZR Codes 65590 & 65591 Actually Mean?

First things first, let’s translate what your RZR is trying to tell you. These codes are specific and point you in the right direction. They are not a generic “engine problem” light; they are your machine’s way of saying a specific cylinder isn’t firing correctly.

Here’s the breakdown:

Code 65590: Engine Misfire Detected – Cylinder 1. This is the cylinder on the PTO (Power Take-Off) or clutch side of the engine.
Code 65591: Engine Misfire Detected – Cylinder 2. This is the cylinder on the Mag (Magneto) or stator side of the engine.

A “misfire” means the combustion cycle in that cylinder is incomplete. Essentially, the mixture of air and fuel isn’t igniting when it’s supposed to. When the Engine Control Unit (ECU) detects this, it triggers the check engine light and often puts the vehicle into limp mode to prevent catastrophic engine damage from unburnt fuel washing oil off cylinder walls or damaging the catalytic converter.

Before You Grab a Wrench: Essential First Steps

Hold on, tiger. Before you start tearing into the engine, let’s do some quick detective work. Sometimes the solution is simpler than you think. This is one of the most important polaris rzr code 65590 and 65591 tips we can offer.

First, safety is paramount. Make sure the engine is completely cool to avoid burns. If you’re going to be working on the electrical system, it’s always a good practice to disconnect the negative battery terminal.

Now, ask yourself a few questions:

Fuel Quality: Did you just fill up from a questionable gas can or station? Old, separated, or water-contaminated fuel is a common culprit for misfires.
Recent Events: Did the code appear right after a deep water crossing or a high-pressure wash? Water can easily find its way into electrical connections or spark plug wells.
Initial Check: Pop the engine cover and just look. Is a spark plug wire loose or disconnected? Do you see any obvious damage to wires or hoses?

Taking a moment to assess the situation can save you hours of unnecessary work. If nothing obvious stands out, it’s time to move on to a more methodical diagnosis.

Your Step-by-Step Polaris RZR Code 65590 and 65591 Guide

We’ll tackle this like a pro mechanic would: starting with the easiest and most common culprits first. This process is all about the “Big Three” of combustion: Spark, Fuel, and Air. A misfire is almost always a problem with one of these three elements.

Step 1: Inspect the Ignition System (The Usual Suspects)

The ignition system is the number one cause of misfire codes. It’s exposed to extreme heat and vibration, making its components prime candidates for failure.

Check the Spark Plugs
Your spark plugs are the workhorses of the ignition system. Pull the plug from the cylinder that’s throwing the code (Cylinder 1 for 65590, Cylinder 2 for 65591). You’ll need a spark plug socket and a ratchet.

Look for Fouling: Is the tip black and sooty (running rich) or oily? Is it white and blistered (running too hot/lean)?
Check the Gap: Use a feeler gauge to ensure the gap is set to your machine’s spec (check your owner’s manual).
Inspect for Damage: Look for any cracks in the ceramic insulator. A cracked plug will arc to the engine head instead of firing in the cylinder.

When in doubt, just replace them. Spark plugs are cheap. We recommend sticking with the OEM-spec NGK plugs for the best performance.

Test the Spark Plug Wires and Coils
The spark has to travel from the ignition coil to the plug. A bad wire or coil will stop it in its tracks.

First, inspect the spark plug boot and wire for any cracks, burns, or corrosion on the terminals. Ensure the boot “clicks” firmly onto the spark plug and the coil.

Here’s a pro diagnostic trick: If you have a code for one cylinder (say, 65590 for Cylinder 1), swap the ignition coils between Cylinder 1 and Cylinder 2. They are usually identical and easy to switch. Clear the codes and run the engine. If the code changes to 65591 (Cylinder 2), you’ve just proven you have a bad ignition coil. No guesswork needed.

Step 2: Investigate the Fuel System

If your spark is strong, the next place to look is fuel delivery. Your engine needs a precise amount of fuel to fire correctly. This is one of the most common problems with polaris rzr code 65590 and 65591.

Clogged Fuel Injectors
Fuel injectors can get clogged with debris or varnish over time, preventing them from spraying the proper amount of fuel. A quick way to check if an injector is working is the “screwdriver stethoscope” method. Carefully place the metal tip of a long screwdriver on the body of the injector and put your ear to the handle. You should hear a distinct, rapid clicking sound. If it’s silent or sounds weak compared to the other injector, it may be clogged or faulty.

Running a high-quality fuel injector cleaner through a tank of gas can sometimes solve minor clogs.

Fuel Pressure
Low fuel pressure from a weak fuel pump or clogged filter will starve the engine for fuel, causing misfires, especially under load. Checking fuel pressure requires a fuel pressure gauge that you tee into the fuel line. Your RZR should have a specific fuel pressure spec (typically around 58 PSI). If it’s low, you’re likely looking at a failing fuel pump.

Step 3: Check Airflow and Intake

The final piece of the puzzle is air. Your engine needs to breathe freely, and any restrictions or leaks in the intake system can throw off the air-fuel ratio and cause a misfire.

Inspect the Air Filter
This is the easiest check of all. A filthy, clogged air filter will choke your engine. If you just came back from a dusty ride and your filter is packed with dirt, it’s absolutely the first thing you should clean or replace.

Look for Vacuum Leaks
The intake boots between the throttle body and the engine head can develop cracks over time. This allows unmetered air to enter the engine, leaning out the fuel mixture and causing misfires. With the engine running, carefully spray a small amount of carb cleaner or starting fluid around the intake boots. If the engine RPM changes, you’ve found your leak.

When the Misfire is Deeper: Advanced Mechanical Problems

If you’ve checked spark, fuel, and air and are still getting a misfire code, the problem might be mechanical. This is where the diagnosis gets more serious and may require a trip to the shop if you’re not a seasoned DIY mechanic.

A compression test is the next logical step. This test measures the engine’s ability to compress the air-fuel mix. Low compression in one cylinder points to serious internal issues like:

Worn piston rings
A burnt or poorly-seated valve
A blown head gasket

Another potential issue is incorrect valve lash. If the clearance between the valves and the rocker arms is too tight, a valve may not close completely, causing a loss of compression and a misfire. Checking and adjusting valves is part of routine maintenance but is often overlooked.

Best Practices for Preventing Misfire Codes

The best way to fix a problem is to prevent it from happening. Following a few polaris rzr code 65590 and 65591 best practices can save you a world of headaches on the trail. This is the core of a sustainable and effective maintenance strategy.

Think of it as a polaris rzr code 65590 and 65591 care guide. A well-maintained machine is not only more reliable but also more efficient. A clean-burning engine is a more eco-friendly engine, ensuring you’re leaving nothing but tracks behind.

Use Quality Fuel: Always use fresh, high-octane fuel from a reputable station. Use a fuel stabilizer if your RZR will be sitting for more than a month.
Regular Plug Changes: Don’t wait for a misfire. Change your spark plugs as part of your regular maintenance schedule.
Keep it Clean: Keep your air filter clean! After every dusty ride, inspect it and clean or replace it as needed.
Listen to Your Machine: Pay attention to how your RZR sounds and feels. Often, you can catch a minor issue before it becomes a code-throwing, ride-ending problem.

Frequently Asked Questions About Polaris RZR Code 65590 and 65591

Can I still ride my RZR with a 65590 or 65591 code?

We strongly advise against it. A persistent misfire can dump unburnt fuel into the exhaust, potentially damaging the catalytic converter. More seriously, it can indicate a problem that could lead to severe internal engine damage if ignored.

What are the basic tools I need to diagnose these codes?

You can get pretty far with a basic mechanic’s toolset. At a minimum, you’ll want a good socket set with extensions, a dedicated spark plug socket, a set of feeler gauges for checking the plug gap, and perhaps a multimeter for checking electrical components.

Will just clearing the code fix the problem?

Absolutely not. Clearing the code simply turns off the check engine light. If you haven’t fixed the underlying mechanical or electrical issue that caused the misfire, the code will come right back as soon as the ECU detects the fault again.

My RZR is throwing both 65590 and 65591, and maybe 65592 (multiple misfire). What now?

If both cylinders are misfiring, look for a problem they have in common. This is less likely to be a single bad spark plug or coil. Common causes for a multi-cylinder misfire include bad fuel, a clogged air filter, low fuel pressure, or a faulty crankshaft position sensor.

Tackling a check engine light can feel intimidating, but a polaris rzr code 65590 and 65591 issue is often very solvable. By working through the steps logically—from spark to fuel to air—you can systematically pinpoint the cause and perform the repair yourself.

You have the knowledge and the roadmap. Take your time, be methodical, and you’ll solve the puzzle. Get that rig running right, and we’ll see you back on the trails where you belong. Ride safe!

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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.