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How does the safety/interlock system work on Craftsman Lawn Tractor Model #917,271910?

How does the safety/interlock system work on Craftsman Lawn Tractor Model#917.271910?

Craftsman , Lawn Tractors , Lawn Mowers
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4 Answers from these members:
afritz afritz
When I have a question on my item something that like to do is refer back to my owners manual because usually it provides me with lots of answers on questions that I have. I would highly recommend reviewing your owners manual. If you do not have yours I have managed to locate one here on the Manage My Life website. I attached the link below for you to view while you wait on your answer from an expert. I hope this can help you better understand your lawn tractor.
by afritz afritz Earned 13,820 community points in Craftsman
December 19th, 2010
Answered in 10 minutes
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Manage My Life
There are basically 2 safety circuits on this tractor. One affects the starting and the other deals with operator control.

The starting safety circuit ensures that the machine is immobile and that the blades are off to prevent injury. This circuit starts at the ignition switch on terminal "S". When you turn the key to the "start" position voltage is sent from the ignition switch to a switch on the clutch/brake. If that clutch/brake is pushed or locked down, voltage is allowed to pass through to the PTO switch where the same thing is determined. If the PTO lever is up, voltage stops there and the starter is never engaged. If the lever is down, voltage is allowed to pass on to the starter solenoid where the voltage will engage the solenoid and allow a contact to be made to engage the starter and spin the engine over.

The "operator presence" safety circuit works (more or less) between the PTO safety switch, a safety switch on the seat, and the clutch/brake switch. What it is looking for is the seat switch being triggered. If you are on the seat, you can start the blades. If you are not on the seat and you attempt to start the blades, the system is grounded out and the engine shuts down. The same actions take place for the clutch/brake. If you are not on the seat (switch not triggered) and the clutch brake pedal is lifted, the engine will shut down. All this works on the idea that a bad situation can get a whole lot worse if the machine does not stop doing what it's doing if something bad happens. If the tractor turns over, the engine is going to die. If you are not on the seat, it is assumed that you are no longer in control of the machine and it needs to shut down (quickly) to prevent further injury.

The safety circuit on this mower is quite simple and very effective at doing what it is designed to do. I know that every year people try (and some succeed) at bypassing the safety features. In way too many cases, the outcome of that is terrible. I cannot possibly stress enough how important it is to


tamper with the safety circuits. We get reports all year long of situations where people have been maimed or killed because the safety circuit was bypassed and the blades did not quit turning when they should have. It's very easy to assume that I know what I'm doing on a tractor and I don't make mistakes. That's human nature to make that assumption about something you do weekly. But accidents are called accidents because they are just that. If they were normal, they would not be called accidents.

A quick story of my own to demonstrate how easy it is to just not think when something very abnormal happens. My house back home as 10' glass doors all the way across the front of the house. I've mown that yard well over 100 times. I came across that stretch one afternoon and caught a rock from someone and sent it through that window. One of my nieces was sitting just on the other side of that window when it crashed in. I was moving and the tractor, saw the glass go everyone and immediately stood up to get off and go check on my niece. Had the safety circuit been bypassed (because I do know how to do it), I would have likely lost a foot when I stepped down because the 50" deck does not know my foot is there. The safety circuit caught the fact that I had left the seat and immediately stopped the engine. Everybody was ok and I just had to replace an $800 window.

I work on these machines a lot and I came right off the seat and never though another thing about it. It is human nature to make those sort of mistakes and the manufacturers to the best they can (within reason) to help us not hurt ourselves.

So, that's my safety circuit speech. If you are having problems with yours, please reply back to me here on this thread and I will help make sure yours is working as it should be.

Thank you for using Manage My Life!
by Manage My Life
December 20th, 2010
0 votes
Manage My Life
Hello Wade, I recently picked up a Craftsman 15 HP Ride-on mower, Model #917256552 on the side of the road, the owner had a free sign on it and he told me the engine ran fine but the interlock system was not working. I am very anxious to give this old mower a new life, but i don't know where to start, the battery for the mower is new, and its fully charged, but even when I sit on it and lock the brakes the Mower won't start. The mower is missing its cutting deck, does this affect its ability to turn on? When i turn the key the little dial on the front of the machine moves, indicating battery power. I know very little about ride-on mowers, where would i start to find out what may be causing the interlock safety feature to be faulty?
by Manage My Life
August 22nd, 2013
0 votes
Mark T
I am sorry you are having this problem with the tractor. I recommend determining what is causing the engine not to turn over. First, make sure the engagement lever is down or the PTO button is pushed in and the brake pedal is fully depressed or the tractor will not attempt to turn over. If you have already done this, I recommend checking the fuse. The fuse is located behind the dash. If the fuse is good, you have a wiring or switch problem. The easiest way to pin point the problem is with a volt meter. If you do not have a meter, you can purchase one relatively cheap.

Turn the meter to check dc volts, and then hold the black lead to the black negative battery terminal for all of the voltage checks. Place the red lead on the positive terminal of the battery. The reading should be 12 volts. If you have a 12 volt reading, move the red lead to the first blue dot in the image. Your reading should be 12 volts. If you have 12 volts, have someone sit on the tractor and hold the brake pedal while turning the key for the rest of the checks. While they have the key turned to the start position, move the red lead to the next blue dot. The reading should always be 12 volts. Then move to the next blue dot. If you lose the 12 volts, the problem is between the last blue dot you had the voltage and where you lost the voltage. If you have 12 volts all the way to the white wire on the solenoid, the solenoid or the starter is defective.

To determine starter or solenoid short the two large posts on the solenoid together with a screwdriver. There should be a spark it is normal. Once shorted the starter should run.

If the tractor still will not run once you get the starting issue fixed, please let me know. I will be happy to assist you with diagnosing that.

Thank you for using Manage my life.

Mark T.
by Mark T Earned 58,303 community points in Craftsman
August 23rd, 2013
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