455 Blows PTO Fuse

[Wiens]

Fellow JD diesel owners/mechanics,

I need some help. My new to me 455 is blowing the "F-6" fuse, at least that's what the dealer called it. It's the top fuse on the two on the circuit board. I mowed for two hours on Tuesday when it was cool outside and had no problems. Today I mowed for 20 minutes and it blew the fuse. It was around 95-100 degrees. After trying to find why it didn't start I found the blown fuse and I replaced it. It had sat for about an hour and had cooled down. It ran fine for another 20-30 minutes and did the same thing. I replaced the fuse and started it up and it blew within 5 minutes. This went on for 5 more times until I ran out of 15, 20 & 30 amp fuses. I was scared to try the 50 or 75 amp. If I leave it set for 30-60 minutes it runs fine until it gets warm. The temp gauge didn't show more the 1/4 to 1/3 up.

Is the PTO circuit connected to the temp sending unit as a fail-safe? I will be able to borrow the tech manual for my local JD dealer but was wondering if anyone had prior experience with this problem or had a tech manual they could look up the testing procedure. The tractor is a 2001 model, serial number 90,000+. It has only 500 hours on it and is clean and appears well maintained. Coolant is full, the side grills are and have been cleaned and the radiator screen is kept clean during mowing. I greased the mower deck spindles before mowing. Nothing seems to be binding in the deck.

I'm at a loss, however, I suspect something in the cooling circuit may be causing the fuse to blow. What do you think?

Thanks in advance,

Kevin in Kansas

 

[Glenn9643]

I haven't read the manual regarding this, but our 455 will shut the pto off when it overheats, and it will start and operate normally after cooling. So far we haven't had any fuse problems.
Shutdown point on ours is at or near the "redline" area of the temp guage. I was cutting yesterday and had to stop and clean the screens/blow out the radiator fins, and after that it ran cool.
Sounds like there's a short somewhere in this safety switch circuit. Good luck.

 

[awlchu]

Wiens,

I find it hard to believe it is a temperture related problem. I mean, the increase operating temp is causing the blown fuses. It is driving another problem.

The resistance of the circuit is dropping so quickly that the current increases beyond the fuse. A path must exist between the 12v and zero ground for you to blow a fuse.

Is the PTO internal to the rear differential? On my X485 a electric solenoid is activated and engages the internal PTO. I believe the circuit from the PTO switch is protected by a relay (separate the high current from the user).

1- The solenoid is a device containing very fine wire windings. Possible the windings are shorting against the internal core/mechanism of the solenoid (at temp) causing the short.

2 - The relay that closes the circuit is shorting at temp. It is quite possible the internals of the relay are shorting.

3- Chafing of a harness is possible be unlikely. Look for disconnects, disconnect them from each other and with a flashlight inspect the crimping of the wires on the pins. f possible pull back the outer insulation and look for stray strands of wire that might not have been crimped onto the pin. What I have done is separated each circuit (and with the power OFF) used a paper clip and a continuity meter (beep when a circuit is closed) to look for internal shorts. You short one end of the harness with the clip, then connect the meter to the other end, then wiggle the harness throughout it's length.

 

[awlchu]

Do not replace any more fuses greater than factory value.

 

[jd455]

I looked at my tech manual and the high temp sensor is tied into the PTO circuit. Two of the items to test in the PTO circuit test procedure are:

Engine high tem relay terminal (87A), should have no voltage, if not normal replace high temp relay

Coolant temp switch, should have no continuity to ground with coolant temp below 110C, if not normal replace coolant temp switch

Whole procedure is two full pages plus two pages of diagrams, let me know if you need more.

Good luck!

Mark
NH

 

[Wiens]

Well, I think I found the problem to the fuse blowing on my 455. The wiring harness on the left inside frame rail has has a connector for the rear PTO option. After I transferred my rear 540 PTO from my 425 to my 455 I noticed two cut wires (RIO) and one pink/white wire (RIP) that looked like it had its insulation stripped back 1.5 inches . From what I can tell it would short on the frame. I haven't been able to use the tractor yet as I encountered a few small problems with the rear PTO.

I hopefully will be able to use the mower in the next two evenings. I'll keep you posted.

Kevin in Kansas

 

[awlchu]

Good!

You can save the wires by using some heat shrink tubing.

Also, check to see why the wire were loose, missing tie straps?

 

[joe patterson]

Good!

You can save the wires by using some heat shrink tubing.

Also, check to see why the wire were loose, missing tie straps?

my 455 jd blew 15 amp fuse on ctl board when pto was turned on, found pto selenoid on rear of trans, was apperantly shorted internally, showing vert low owms compared to a new one. about $150.00 at deere, cheaper on line, but dealer in stock and let me ohm parts before buying. thought that was better than the few bucks saved and waiting several days. part # AM878297

 

[Industrial Toys]

Unfortunately, heat shrink is only good if you can get it over the end of the wires.

Often it seems that a fuse blowing after heating up is a shorting solenoid coil. Just had that on my old 770. Hold coil on fuel solenoid was going bad.

Is the PTO fuse for a sonenoid (engagement) or just for safety circuits?

 

[joe patterson]

yes . PTO switch turns selenoid on, running fine after replacing . found selenoid hot to touch after about 10 min engaged. never checked it before now so this may be normal.