4720 won't crank - both PTO indicators lit...

[Karl2]

I was driving my tractor down my driveway with garbage bags in the bucket, I stopped and hopped out at the end of the driveway to throw the trash in the bin when all of a sudden my tractor just stopped. It stopped the same way it does when I inadvertently get off the seat while PTO is engaged. But it didn't stop as soon as I left the cab, I had been out a good 30 seconds when it died.

At first I thought I had inadvertently pulled the PTO knob while getting out but when I went back to the cab and checked the knob was down. Tried starting it but no go, not even a click. Battery is fine, all the lights burn bright and electrical equipment works as it should. However I get a "PTO on" message when I try to start and two of the three PTO indicators are lit. That's right, two indicators are lit one saying 540 rpm and the other 2000 (approx. figures) so obviously the reason the tractor won't start is because it "thinks" a (or two) PTO(s) is/are engaged.

Problem is, I only have one PTO (rear) on this tractor and I'm quite sure it can't run at two different speeds at once. And besides, it is not turned on and there is currently no attachment to the rear PTO. Up until today the tractor ran fine.

If only I could clear this error I know it would start but I have no idea how to reset this

Any ideas?

Thanks in advance!

 

[Karl2]

Alright, after a bit of -hopefully- logical thinking I believe that the most likely culprit must be a faulty/jammed PTO safety switch or detector. Since there's no way the tractor will ever start with the safety device jammed at the "on" position I figure I gotta find a way to either un-jam it or temporarily bypass the PTO safety switch so that I can at least get the tractor to start and remove it from the driveway and use it until I can get a replacement part for the PTO safety detector or whatever it's called.

Does anyone know the approximate location of this device on the 4720 or similar models? I suspect it's underneath the PTO knob somewhere but I wouldn't want to start dismantling just about every panel in the cab if it's located elsewhere. Unfortunately I don't have a shop manual so no wiring diagram

 

[Karl2]

Okay done some digging and found some crude drawings of the 4720's electrical system in the parts catalog on the JD site. There appears to be no separate safety switches at all other than the seat switch, however perhaps the PTO switch itself (part #LVA11437) has a built-in safety feature?

On another forum someone suggested I short the seat switch. Since I have the air ride I don't have easy access to the switch itself but I suppose shorting the connector that leads to it from a harness behind the it would do the trick?

I can't see how bypassing the seat switch would do anything for me though, the way I see it the reason the engine won't crank is because the PTO indicators are lit and the "PTO on" error message appears on the LCD display indicating that the computer is blocking power from reaching the starter or something of the sort.

From experience I think that on ehydro models the seat switch has no other purpose than to stop stop the engine should the operator leave the seat with engine running and mid PTO engaged, or if the rear PTO is engaged with transmission not in neutral and park brake not set. Therefore the seat switch has no effect on anything as long as the engine is not running, at least on ehydro models.

Anyway it's pretty clear that the engine won't crank as long as the computer thinks PTO is engaged regardless of the seat switch. I guess that if I can't un-jam the PTO switch I'll just have to bypass it until I get a new switch, no big deal since I don't need to run any rear implements for a couple of weeks.

I still don't understand why two PTO indicators are lit since there's only one PTO installed on this tractor... could it be because the same switch controls both PTO's when two are present?

 

[AKfish]

Try the "operator out of the seat while operating the pto" sequence. Transmission in neutral with emergency brake locked.

See if the engine will start.

If you can locate the pto safety switch - try to jump the connector by unplugging it from the wiring harness and shorting it with a piece of electrical wire.

JDparts should give you a fairly good idea where to find the switch.

Good luck.

AKfish

 

[Karl2]

Try the "operator out of the seat while operating the pto" sequence. Transmission in neutral with emergency brake locked.

Thanks for the reply, I wasn't hopeful I would get any on this gorgeous springtime Saturday evening

The operator off seat sequence is one of the first things I tried but it didn't work. I wasn't really expecting it would since this procedure is to be done after the engine has been started normally, but I gave it a try anyway. From what I gather a lot of late-model tractors including the 4720 simply won't start with PTO engaged (or when the computer thinks it's engaged even when it's not) even with operator on seat.

If you can locate the pto safety switch - try to jump the connector by unplugging it from the wiring harness and shorting it with a piece of electrical wire.

According to JD Parts on the 4720 there is no separate safety switch for the PTO, just the standard PTO rocker switch. Even though they don't say it in so many words I guess it would make sense that the safety feature is embedded in the main switch itself. If it's the case this would constitute a deterrent for those who'd want to disable the safety feature and be able to start the engine even with PTO engaged, since bypassing the main switch would disable the PTO altogether. Could help prevent lawsuits against the manufacturer as well. Just a thought.

So tomorrow morning I'm going to follow your suggestion and either disconnect or short/bypass the PTO switch altogether, hopefully this will allow me to start the engine. Logically, simply disconnecting the switch should work. After all it must be the lack of a return signal that tells the computer the PTO is not engaged? I hope so.

JDparts should give you a fairly good idea where to find the switch.

Good luck.

Thanks and yes indeed JDparts was an excellent resource for locating the position of the parts on the electrical system. If I had known that before instead of losing patience maybe the tractor wouldn't still be in the driveway by now, he he.

 

[AKfish]

I considered your suggestion to simply disconnect the pto switch. Which you could do by simply removing the fuse from the main fuse panel. But... I think the tractor will still not start given that when the fuse blows - the tractor likely shuts down and will not restart until you replace the fuse.

However, at this juncture (and on a Sunday) it's probably worth a shot, anyway.

Good luck and keeps us posted.

PS - hope it's not your computer that's "fried" ... Darin just had his replaced and he figured it was around $1,500!!

AKfish

 

[Karl2]

I considered your suggestion to simply disconnect the pto switch. Which you could do by simply removing the fuse from the main fuse panel. But... I think the tractor will still not start given that when the fuse blows - the tractor likely shuts down and will not restart until you replace the fuse.

There is no fuse for the PTO circuit, could be that the switch itself has a fuse or a breaker within its casing I suppose but I suspect it's simply because the PTO is not powered by the electrical system therefore doesn't require circuit protection since a circuit who simply goes to a switch and back without powering anything is either not likely to surge, or has self-contained protection. I also noticed that none of the cruise control circuits have corresponding fuses on the panel either. All of these appear to be very basic, extremely low-amperage circuits.

However, at this juncture (and on a Sunday) it's probably worth a shot, anyway.

On a Sunday almost anything is worth a shot

PS - hope it's not your computer that's "fried" ... Darin just had his replaced and he figured it was around $1,500!!

Yeah I was a little alarmed when I read that thread but there is a major difference between his problem and mine: he had no error messages when trying to start while I definitively have one ("PTO on" error) that makes it pretty clear why it won't let me start.

Also in the Ford/New Holland forum a few minutes ago I finally found someone who had the exact same problem. The member who replied also had this issue occur intermittently and when it does he solves it by "resetting" the PTO switch, apparently this involves some vague fiddling with it, and this causes the PTO lights to go off allowing him to start the engine. From their description on the NH tractors this switch is much easier to access than it is on JD's, but this gives me good hope.

 

[jenkinsph]

Karl, if nothing else works why not try disconnecting the battery lead for a few minutes to see if this resets the computer? I think it is worth a try.


Steve

 

[Karl2]

Karl, if nothing else works why not try disconnecting the battery lead for a few minutes to see if this resets the computer? I think it is worth a try.


Steve

Thanks for the suggestion Steve. Had to deal with a minor emergency this morning so I couldn't tend to the tractor but I'm getting to it right after lunch. Will try the battery thing prior to removing panels to get at the switch.

 

[sunnyside360]

Karl, if nothing else works why not try disconnecting the battery lead for a few minutes to see if this resets the computer? I think it is worth a try.


Steve

Took the words out of my mouth.... urrrr computer.