Reasons Why Your Jet Ski Won’t Start

It’s time to update this post after answering hundreds of comments from readers and helping them with their jet ski starting problems.

I’ve added more things to try when your jet ski is refusing to start, along with many new tips. It can be frustrating when your jet ski won’t start, but with this new updated guide, it will help you figure out why.

Why Your Jet Ski Won’t Start

A jet ski not starting is most often a dead or weak battery. A bad starter relay can also be another reason for a jet ski not starting.

Usually, when you hear multiple clicks from your jet ski, it’s a bad battery and if it’s one click it’s a bad starter relay.

A bad battery and starter relay are the most common reasons for a jet ski to not start, but here is a list of other things that can cause starting problems that we’ll go over in this post.

1. Bad or weak battery.
2. Bad starter relay.
3. Bad spark plugs.
4. Bad or wrong key or Locked.
5. Sucked something up.
6. Bad starter button.
7. Bad fuel injectors.
8. Blown fuses.
9. Bad ground connections.
10. Bad gas.
11. Bad fuel lines if it’s a 2-stroke.
12. Bad starter motor.
13. Bad fuel pump.
14. Hydrolocked.
15. Broken safety lanyard or not attached.
16. Fuel selector is not on, 2-strokes only.
17. TOPS switch is bad.
18. ECU or ECM is bad.
19. Overheating/cooling issues.
20. Throttle position sensor bad.
21. Blown engine.
22. Damaged gauge.

1. Bad Or Weak Battery Can Keep A Jet Ski From Starting

The most common reason for a jet ski to not start is a bad or weak battery.

You can tell it’s a bad battery if you press the start button and all you get is multiple clicks coming from the engine compartment. That multiple clicks are the starter relay clicking because the battery doesn’t have enough power to turn the engine over.

If you put the key on and the gauges do not come on, it is another clue that the battery is dead. A completely dead jet ski battery won’t have enough power to turn on the display or make any noises.

Even if the battery seems fine or is brand new, it still can be a bad battery.

The only way to test if a battery is good is to use a load tester. Testing the voltage doesn’t mean anything, you need to test the amps, and only a load tester can do that. You can take the battery to any autoparts store and have them load test it, or buy a load tester (Amazon Link Ad) to keep in your home.

The best jet ski battery and the correct size to get can be found in our “The Best Jet Ski Battery + What Size You Need” post.

A battery being bad at the start of the season is quite common. Batteries go flat if they’re not used for months, so it’s important you keep a battery charger on your jet ski battery in the off-season. The best battery charger and other questions relating to your jet ski batteries is covered in this post.

2. A Bad Starter Relay

The next most common reason why a jet ski won’t start is that the starter relay(solenoid) is bad.

You can tell the starter relay is bad if you only get one click or thud from the engine compartment when you press the start button. The gauges will come on when you try to start, but all you get from the jet ski is one click, that is a sign of a bad starter relay.

The starter relay is a component that takes the lower power coming from the start button and has it control a high-power wire coming from the battery. The high-power side goes directly to the starter motor to turn the engine over.

It’s not uncommon that you need to replace your starter relay for your jet ski at least 2 to 3 times within its lifetime. You can’t predict when your jet ski’s starter solenoid will fail, it’s random, but it will always give a solid thud when it does fail.

Starter relays are not hard to replace for most jet skis, it’s often two mounting bolts, plus two terminal nuts and disconnecting the low power side wires. It can be dangerous replacing the starter relay, so be sure to disconnect the battery fully before doing anything.

3. Bad Spark Plugs

If the jet ski engine turns over but refuses to fire up or sputters a bit, then that is often a sign of bad spark plugs.

The jet ski may even fire up, but won’t stay running or runs very rough.

Ideally, you should change the spark plugs in your jet ski every year, at the start of the season is the best time. Here is a list of maintenance items you need to do for your jet ski.

4. Bad key, wrong key or Locked

Customers putting on the wrong key is more common than people realize.

It’s not uncommon for a jet ski owner to get two jet skis and the keys not be programmed alike. The keys look the same, but if you have a Sea-Doo and put the wrong key on the jet ski it won’t start as each key is programmed to each machine. If you own multiple Sea-Doo’s ask your dealership about getting all your keys programmed alike to keep this from happening.

If it’s the right key, there is a chance the key or post could be bad. While rare, I’ve seen a few number of Sea-Doo keys go bad and the only fix is to get a new key. The post where the key plugs into can go bad too, one way to test that is to put a strong magnet up to it and if the Sea-Doo doesn’t beep the wrong key sound then the post is mostly likely bad.

Yamaha waverunners have some models that have key fobs, and you can lock the jet ski like you do your car. If your Yamaha has the key fob or a PIN code access, make sure it’s unlocked before trying to start it.

Kawasaki has keys similar to Sea-Doo that go in the glove box, so make sure they’re inserted before attempting to start.

5. Sucked Something Up Into Jet Ski Pump

It’s a good idea to check your jet pump for anything inside it like ropes, rocks, sticks or any large item that’s not supposed to be there.

Jet skis are direct drive, this means the jet pump is connected to the engine, there is no transmission. So when you go to start the jet ski, the jet pump will also spin and if something is stuck in the pump, it will keep the engine from starting.

One of the first things you should check when you get the jet ski out of the water for a non-starting problem is the pump. Look from the rear and also safely crawl under the jet ski to look into the pump to make sure nothing is blocking the pump blades from moving.

If you need to remove something from the pump, I have a post here to show you how.

6. Bad Starter Button

A bad starter button can keep a jet ski from starting and was a common problem for 2-stroke jet skis.

The rubber of the start button can wear out and cause it to not work. The plastic start buttons didn’t give much trouble, but the rubber ones do wear out quicker.

If the button is torn, you have to press really hard with your nail, or the button is super faded, then replacing the start button is a good idea.

Do note, the start button of a jet ski is not the same as your car. You must hold the start button down on your jet ski until it’s fully started. Pressing the start button once on a jet ski will not start it, it needs to be held down until the engine gets going.

7. Bad Gas

If the jet ski turns over but won’t fire up or runs rough, and you replaced the spark plugs, then it’s most likely bad gas.

Gas goes bad when you let it sit without adding fuel stabilizer to it. It’s getting even worse with more ethanol is added to gas.

If your jet ski has been sitting for a while, then it’s a good chance the gas is bad and keeping your jet ski from firing up. Safely remove the old gas and add fresh premium gas to your jet ski.

This is why I like to store my jet ski near empty (1 or 2 bars of gas) in the off-season and when the season starts I fill it up with fresh 93 octane gas. Along with new spark plugs, you’ll be starting the season off right.

8. Blown Fuses And Relays

If you get nothing out of your jet ski when you put the key on or press the start button once, then it could be fuses or relays located in the fuse boxes that have gone bad.

Locate the fuse box, often near the battery, and check every fuse. If a fuse is blown you need to replace it.

Don’t forget to check the fuses that may not be in the fuse box, there are often fuses inline coming out the fuse box or near the battery wrapped in a rubber sleeve.

It’s not uncommon for me to see a jet ski blow a fuse because someone hooked the battery up backwards. Other times fuses blow just because, there is no good reason except the fuse was not good. If a fuse keeps blowing, you need to figure out what is blowing it.

There are also small relays, look like a small black box with multiple terminals, that go into the fuse box area. These smaller relays are used to power on the low-power items and get the jet ski into turning on mode. There is no good way to test these relays unless you have an ohm meter, but if you’ve gotten to the point of testing them, it’s just easier to replace them. These little relays are less likely to fail than the main starter relay, but they can fail.

9. Bad Ground Connections

If a jet ski is older, corroded ground connections are quite a common problem for starting issues and many other problems.

If you have corrosion around the battery terminal cables, then it’s mostly likely your problem. Corroding battery cables also mean the ground wires that connect to the engine block are corroding too.

You will need to clean all the ground connections, including where they connect to the engine block.

10. Bad Starter Motor

A starter motor going bad is more likely on 2-stroke jet skis than 4-stroke, but it can happen to both.

One way to tell it’s the starter motor that is bad is if all this below is true.

1. Battery is good.
2. Starter relay is good.
3. Nothing is in the pump.
4. Engine is not hydrolocked.

If the above is true, then it’s most likely a bad starter motor.

If you have a 12-volt test light probe (Amazon Link Ad), you can see if the starter motor is getting power to it. Clamp the negative to the battery or ground and put the probe light on the positive connection of the starter and press the start button. If the probe light turns on when you press start, then you’re getting power to the starter, and the next thing you need to do is remove the starter and bench test it. If you get no light from the probe, then the problem is before the starter.

To bench test a starter motor, you have to remove it from the engine and put it in a bench vice clamp and hook it directly to a battery. Starter motors are very jumpy, so you need to make sure it’s secured tight in the vice clamp before connecting it to a battery.

11. Carburetor Issues Or Bad Fuel Lines (2-Strokes Only)

If you have a 2-stroke jet ski that has a carburetor, then a super common starting problem is a clogged carburetor or old fuel lines.

If you have a 4-stroke jet ski, then this section is not for you, as all 4-stroke jet skis are fuel injected. You’ll know you’ll have a carbureted jet ski engine if you have a choke cable.

With the rise of ethanol in gas, it’s been doing a number on 2-strokes carburetors and fuel lines.

The solution is to clean the carburetors and replace the fuel lines, and then avoid ethanol gas as much as you can.

12. Bad Fuel Injectors

Not super common, but bad fuel injectors can keep a jet ski from starting.

Bad fuel injectors can also cause “ghost” problems when it comes to starting. If the jet ski will start but not start again after sitting or is rough to get going, it could be the fuel injectors.

I’ve had a jet ski that would start but if you let it sit for a bit it would refuse to start back up. One of the fuel injectors was leaking and dumping gas in, causing the engine to be flooded and refuse to get running.

Messing with fuel injectors is a dangerous repair and should only be done at the dealership.

13. Hydrolocked Jet Ski Engine

A jet ski that is hydrolocked means there is water in the engine, which is not a good thing.

You can get water in the jet ski engine from it sinking, drain plugs left in and flooded by rain water, broken cooling components and more.

A hydrolocked jet ski engine will refuse to start, and trying to start a hydrolocked jet ski can bend piston rods and do further damage. If you flipped your jet ski, follow these steps.

An easy way to test if there is water in your engine is to take the dipstick out and see the color and consistency of the oil. If the oil is runny and looks like chocolate milk, then that is bad. You want the oil to look amber or black and should not be runny.

Another way to see if water is in the engine is to remove the spark plugs and turn the engine over. If you get a geyser of water shooting out the spark plug holes, then there is water in the engine.

Hydrolocked engine is best fixed at the dealership or repair shop, especially if it’s a 4-stroke jet ski. You’re going to need several oil changes and the intake taken off to get all the water out.

14. Bad Fuel Pump

A fuel pump that is bad can keep a jet ski from starting, but fuel pumps going bad are not common and more of a fluke failure.

If the jet ski turns over, you’re getting spark, but the jet ski does not prime or no gas is coming out the fuel injectors it’s mostly a bad fuel pump.

Another way to tell it’s a bad fuel pump is if the gas gauge is not working, as that is a part of the fuel pump.

The fuel pump is located in the gas tank and is a dangerous repair and should only be done at the dealership.

15. Broken Safety Lanyard Or Not Attached

All jet skis have a kill switch called a safety lanyard that attaches to you and the jet ski. So if you fall off the jet ski, the engine will shut off.

Sea-Doo’s safety lanyard is the key, while Yamaha and Kawasaki have dedicated lanyards on the handlebars that wrap around your wrist.

You need to make sure the lanyard is attached to you and connected to the switch on your jet ski, or else it won’t start.

The switches for the safety lanyard can fail, especially if water gets near the contacts.

It’s recommended you let the dealership repair these lanyard switches, as it’s meant to save lives and needs to be done properly. Make sure your waverunner doesn’t have a recall on the kill switches either.

Tip: If your safety lanyard cable is stretched, damage, or broke, you have to replace it. They do not sell the cable/string separately, so you must replace the whole thing, which means for Sea-Doo you need to get a new key.

16. Fuel Selector Is Not On Or Broken (2-Strokes Only)

If you have a 2-stroke with a carburetor, you’ll most likely have a fuel selector.

The fuel selector can be moved to off, which shuts off all gas to the engine and can keep it from starting.

Make sure the fuel selector is in the “ON” or “Reserve” position when trying to start your jet ski.

An interesting way to know if your fuel lines are going bad is if the jet ski runs fine in reserve but not while in the “ON” position. People don’t use the reserve much, so the lines don’t wear out as quickly.

17. T.O.P.S Switch Triggered

The T.O.P.S Switch (Tip Over Protection Switch) is a switch that is used to determine if your jet ski is upside down. If the switch thinks you’re upside down it shuts the engine off.

The T.O.P.S Switch is used to protect your engine if you flip it and to protect you from the spinning impeller blades.

The old T.O.P.S Switches were simple mercury switches, and they could get confused about what’s up and wants down. The newer T.O.P.S Switches are more reliable, but can still fail.

If you feel like you’ve tried everything else, this is a good one to try. The only good way to tell if a T.O.P.S Switch is bad is to hook it up to the diagnostic computer, as it will throw a fault code.

A bad T.O.P.S Switch will keep a jet ski from starting, and it’s one of those things you’ll try last because it’s not common for it to fail, especially for newer jet skis.

18. ECU or ECM Is Bad

A bad or damaged ECU or ECM can keep a jet ski from starting.

The ECU (Engine Control Unit) and ECM (Engine Control Module) are the “brains” of your jet ski.

If you tried everything else and the jet ski won’t start or won’t run right, then the last thing to check is the ECU or ECM.

Unless you got the proper testing equipment from the manufacturer, it’s hard to know if the ECU or ECM are bad. Most dealerships don’t even get the testers out and just replace it with a known good computer to see if they’re bad or not.

ECU and ECM’s each cost about $1,000 to replace and will require a dealership to program them to your jet ski.

19. Overheating And Cooling Problems

If a jet ski overheats for too long, the computer will kill the engine to protect itself.

An overheated engine can refuse to start until it’s cooled back down.

If the jet ski is refusing to start back up after riding, you may have overheating problems. If you do have overheating problems, alarms should be going off to warn you.

Make sure you don’t run your jet ski out of the water for no more than 15 seconds.

20. Throttle Position Sensor Is Bad

Not super common, but a bad throttle position sensor can keep your jet ski from starting.

Fuel injected jet skis, which all 4-stroke are, will have a sensor to determine the throttle positions. If the jet ski throttle is in too much, the jet ski will refuse to start as it’s in drown mode.

Sea-Doo mostly, if you hold the throttle all the way in it goes in a drown mode which kills the fuel injectors. This mode is for testing things like compression and to make sure the engine spins without firing it up.

If the throttle sensor is not set right or confused, this could be why your jet ski won’t start. To reset this, you’ll need to hook the jet ski up to the diagnostics computer to reset the TPS.

Also, make sure you’re not touching the throttle when trying to start your jet ski. I know a few dirt bike and motorcycle guys that are in the habit to give a little gas to start them, but this is not something you do for a jet ski.

21. Blown Engine

A blown jet ski engine can refuse to start or not run well.

You can tell if a jet ski engine is blown by checking its compression with a compression gauge. You want the PSI to be over 100PSI and each cylinder to be within 15% of each other.

An engine that was hydrolocked and not taken care of properly can also blow the engine.

Running improper fuel and air mixture can lead the engine to blow too.

Running the engine to where it overheats and damages it can also blow the engine.

There are many things that cause a jet ski engine to blow, but it’s usually something major that happened to lead to such events. While a jet ski engine blowing can cause it to not start or run right, it’s not always the case and is one of the more rare reasons.

22. Damaged Gauges

A damage gauge could keep the jet ski from starting or confuse you into thinking the battery is bad. A damage gauge could keep from lighting up and ringing the buzzers too.

The main communications you have with your jet ski is the gauge and the buzzer, so if both don’t come on, it could keep you from getting your jet ski started or knowing what’s wrong.

Jet Ski Won’t Start In Water

If your jet ski will start when out of the water but won’t start when in the water, then the most likely problem is the battery or starter motor.

Jet skis are a direct drive system, so if the engine is spinning, so is the impeller. When the jet ski is put in the water, the starter motor and battery need to now work against the water, so if either one is bad or weak the jet ski won’t start.