Sidewinder / Thundercat won’t start – Frozen Relays Sidewinder / Thundercat won’t start – Frozen Relays
One of the more annoying problems with a snowmobile is when it doesn’t start. Even worse is when it starts in the morning when... Sidewinder / Thundercat won’t start – Frozen Relays

One of the more annoying problems with a snowmobile is when it doesn’t start. Even worse is when it starts in the morning when cold, but doesn’t restart the second time.

This has been the case with some of the Yamaha Sidewinder and Arctic Cat Thundercat sleds. Owner turns the key and the engine cranks and cranks but no start.

Let’s back up for a moment. Modern snowmobiles are fitted with a number of electronic components called “relays”. Usually found inside the fuse box, a relay is a method of using a low voltage logic signal to control a higher current load. Like headlights. Or a starter. Or, a fuel pump. The sled’s computer, or ECU, sends a signal to the relay to “turn on” or engage. Inside the relay, more accurately an electro-mechanical relay, is a set of contacts that closes an electrical circuit. The relay gets the signal to engage, and it closes the contacts to turn on the load.

This is how the sled’s computer controls higher current loads and components, and is very common in cars, ATVs, all kinds of equipment. Most of us should be familiar with a starter relay on a car, where when you turn the key the starter relay passes the current from the battery to the starter motor. The key itself can’t handle the amount of current required by the starter motor, so we use the key as the “trigger” to energize the relay, closing the contacts and completing the circuit.

On a snowmobile we have an extreme environment where the relay is asked to perform in a wide range of conditions, from extreme cold to hot underhood temperatures, as well as extreme amounts of moisture and steam being created.

Ah, steam. This seems to be the one that really causes havoc in the Sidewinder and Thundercat models. The turbocharger, more accurately the intercooler, is placed up in the nose of the snowmobile. And, guess where the fuse box with the relays is located? Yep, up under the hood in the nose of the machine. Anyways, when snow hits the warm intercooler it quickly melts and vaporizes and steam is created. Generally, the relays used to control the headlights and fuel pump and such are fitted in a small plastic case, square or rectangular, and may or may not be sealed. Long story short, moisture gets into the relay assembly. Environments that create condensation or frost, like inside a trailer, can make things worse.

Yamaha Sidewinder Won't Start

So what happens is the moisture gets inside the relay, and when you go to start your sled there can be ice or frost inside of the relay creating a layer of insulation between the contacts. And this leads to the fuel pump not getting power, no fuel pressure in the fuel rail, no fuel being injected into the engine, and no starting of the mighty turbocharged engine.

Owners of these sleds have learned to listen for the fuel pump to turn on and come up to pressure when they turn the key. Actually, when cold starting a Sidewinder one wants to let the fuel pump come up to full pressure before turning the key to the next position which engages the starter motor. In colder conditions, many owners will do this twice – turn the key on to pressurize the fuel rail, turn the key off, turn the key back on again and let the fuel pump run a second time, and then when it quits running the second time then they crank the engine. This is in stark contrast to simply twisting the key from full off to immediately cranking the engine, which works fine when the engine is warm but is not the most effective way to do it with a cold engine.

So, if you turn the key on and don’t hear the fuel pump running you could have a frozen relay. If it cranks but doesn’t start, we clearly have a problem. Owners have learned to warm up the culprit relay, melting away the frost and ice inside, so the contacts can flow current and energize the fuel pump. This can be done by warming the entire sled, or by opening up the fuse box and pulling the relay out and warming it, or replacing it with a warm (dry) one. Sometimes it can be a matter of warming it in your hands, taking it inside a warm vehicle and heating it up, or into a warm hotel room to thaw it briefly.

Yamaha experienced a similar situation back with their Apex models a few years back, and came out with a Solid State Relay (SSR) for use on their sleds to eliminate the problem. A Solid State Relay is a totally electronic device with no mechanical function so there are no contacts to close, or freeze. And, they are far more expensive. Now with the Sidewinder there is not an SSR available from Yamaha, but we do have options.

Many Yamaha dealers have learned there is a similar relay, also rated at 20 amps with the same pin configuration, used by Polaris that is better sealed to the elements. Seems Polaris had some trouble on their ATVs and side by sides and sourced a better relay that would perform better in wet conditions. These Yamaha dealers have been installing the Polaris relay, part #4016819, and report improved reliability with the Sidewinder fuel pump. These sell for about ten bucks and seem to perform better, but do not totally solve the problem.

Inside the Sidewinder fuse box there are actually six relays, four of them are just like the fuel pump relay with four pins (rated at 20 amps) and then there are two relays with five pins. A person could always swap any of the four around, but one of the four is the main relay so that would be a bad one to try. The lighting relay would be a better one to swap with, at least your sled would start but might not have headlights until the (frozen) relay warmed up enough to energize. The five-pin relays are used for the reverse servos, so if you have a problem with reverse you might want to start by looking there.

OK, so how about a long term fix? The Polaris part seems to work OK. From what we can tell, it is a “flux sealed” relay with improved sealing (more for manufacturing than environmental conditions). While there are many 20 amp relays available with a similar pin configuration, some will only have a simple dust cap, some with be flux sealed, and some will be what is called “washable sealed”, again referring to manufacturing conditions and not environmental conditions. Even so, the washable sealed relay design seems to be the more durable of the electro-mechanical relay options.

Some riders have even resorted to taking one of the standard relays and sealing the dust caps, using things like epoxy, nail polish, or plastic tool dip, to coat the relay case and try to seal it so moisture simply can not get inside. Others simply carry a spare relay with them so if they should ever have the problem, they open up the fuse box and pull the frozen relay and replace it with a warm dry one. Some have taken to trying to better seal the entire fuse box, focusing on this perimeter seal for the fuse box cover instead. Something as simple as improving this seal could make all the difference.

About the best solution we’ve found is from the same guy that made the black box to fix weak Yamaha handwarmers. He’s taken some of the better relays and has sealed them hermetically sealed (airtight) and then fully encapsulated in epoxy. Dealers who use this exact relay report zero repeat problems. They suggest you replace both the main relay and the fuel pump relay as those are the two that are energized when you turn the key on and need the relay to engage at low voltage before the engine is running. You get these epoxy sealed relays for $40 for a pair of two and they will eliminate the problem. You can order these “No Freeze Relays” from and they actually work on all of the Arctic Cat Procross sleds as well, especially the 7000s and 9000s that use the same fuse box and relays as the Yamaha models.

Moral of the story, knowing how relays work and how they affect the function of your sled can allow you to fix many problems, helpful while in a parking lot or out on the trail. Taking the hood off and opening up the fuse box at -20 degrees is never fun. Some riders will actually replace ALL of the relays on their sled with higher quality, more expensive, sealed units in an attempt to prevent it from ever causing an issue while out on the trail, but the two that need to come on before the engine starts are the critical ones that most often are the issue. And finally, why does Yamaha or Arctic Cat not install better relays to begin with? According to a Yamaha Technical Specialist, they have decided install new “cold weather” 20 and 30 amp relays in the 2020 Sidewinder models. Our bet is dealers will soon be using these to replace any trouble pieces on previous year sleds.

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