[Off_Road_Al]

I’ve got an 03 450 Foreman S and suddenly it won’t stay engaged in 4x4. I put it in 2 wheel the other day and it quit working properly. The 4x4 light comes on when you start it and it stays on for about 30 seconds then goes out. If I gun it it will sometimes come back on and stay on while moving. Eventually it will start blinking 6 times and 4x4 will not engage again until I shut it off and start it again. Then the process repeats

It is not a mud/water machine. The battery is good at nearly 12 volts and charges around 15 when running. The white connector at the right rear wheel is plugged in and tight. The green connector on the front diff is plugged in and tight. I’ve got continuity at the selector switch on the handle bar. Anyone have any ideas? Why would it work for 30 seconds-ish then stop? Who misses the good ole days when your ride was either 4 wheel or not? We’ve got to complicate everything... Any help is appreciated

 

[Carolynskii]

At less than 12volts on your battery it'd be hard to diagnose. Your battery should have over 12volts. It's no less than 12.4 volts I believe. Unless you charge or change your battery it'd be hard to tell.

 

[shadetree]

i have the same atv. odds are, either the 4wd control unit ?, or a bad speed sensor ?.

 

[Off_Road_Al]

The battery charges at nearly 16volts at idle. My battery charger shows it to be at 100% charge. Can a speed sensor mess that up eleven though it’s standard shift? No ESP...?

 

[Off_Road_Al]

A quick bit of research and the final clutch control unit sounds likely. I’m assuming that’s what we’re talking about? FCCU they call it. It’s a new one to me but fits why it’ll sometimes reengage when I gas it. Could be either I suppose

 

[Carolynskii]

You're in good hands with Shadetree he knows these bikes blindfolded lol
Here's a repair manual for your bike. If it's not an electric shift then code 6 is a low voltage problem. Possible battery alternator rectifier or bad connection problem as far as I can tell.
But I promise you shade know more than this manual does lol
https://drive.google.com/drive/mobi...ZJWJYBYx3vJ7s?usp=sharing&sort=13&direction=a

 

[Off_Road_Al]

Thanks for the link to the manual. All good advice I’m sure and I’m grateful. I think I’ll start with the FCCU/speed sensors and go from there. That indicator light has blinked and acted wild for years but the 4wd always worked. Didn’t give me trouble till I selected 2wd this winter to some sliding in the snow. Thanks again! I’ll follow up next break through

 

[shadetree]

The battery charges at nearly 16volts at idle. My battery charger shows it to be at 100% charge. Can a speed sensor mess that up eleven though it’s standard shift? No ESP...?

at 16 volts ?, this tells me your reg/rec is bad, and it's over charging. what i discovered on my '03 trx450fm when i thought the 4wd control unit was bad ?, is it had to be put in gear in order for the front drive to engage. soooo, i bought a new control unit from Honda, installed it, same problem, no 4wd light on the display ?!..hmm..well crap, finally got around to testing the engine while on my lift ( all wheels up ), put it in gear to check the tranny, low and behold, 4wd light came on !!..well crap..bottom line : it has to be running ( in gear ), in order for the front drive differential to engage so it seems. this is why i narrowed it down for you, either 4wd control unit ?, or the front speed sensor..yes..there is a front differential speed sensor on there !, the 4wd control unit needs to '' see '' the atv moving in order for the 4wd control unit to engage for the front.

 

[Off_Road_Al]

I’ve got a control unit on order. If that doesn’t work speed sensor is next and we’ll see what happens. Thanks again! I’ll post results

 

[shadetree]

I’ve got a control unit on order. If that doesn’t work speed sensor is next and we’ll see what happens. Thanks again! I’ll post results

yw, plz keep us updated !.

 

[retro]

You'll need to fix the battery and charging system 1st. 16 volts output at idle speed is way too high! On a good battery fully charged at idle you should see about 14.5 volts max. At 16+ volts the control units on Hondas shutdown to protect themselves due to overvoltage. At approximately 16.5 volts & up CDIs commonly fry... so you are lucky that the bike still runs.

So put a new battery in the bike 1st. Then start the motor and monitor charge voltage for several minutes as the new battery becomes fully charged. If the charging voltage rises above the spec, replace the regulator/rectifier immediately.

Once you fix the battery and charging system your selectable 4x4 control unit will probably function again. Let us know how it goes if you can.

 

[fishfiles]

I have that same atv , mine is a 2002 FW , I think they called them 450S till 2002 when they went to selectable front diffs , I had a problem similar to yours , but mine all started blowing a fuse immediately when I engaged 4x4 , cleaned and dielectric greased every connector and got the fuse to quit blowing , then it started doing the same thing as your , it would engage for 10-30 seconds and then cut out , I had all 4 wheels over the ground and would run it in the air and see it happen , I had a test light probed into the power wire to the front diff clutch and when it would kick out the 4x4 , the voltage was till there , so that told me the problem was in the final diff clutch , I took the plug off the final drive clutch again and cleaned the socket and plug really well with WD40 and scraped the terminals with a pick , then compressed air and packed it full of dielectric grease , it has been ok since ----------------------- but I am no fan of electrical components when not needed , have a 2000 non-electric diff and a 4x2 ready to drop in there if it ever gives me trouble again

 

[Off_Road_Al]

I put a different battery in it last night for good measure and confirmed it’s charging at about 14.5 at idle. It moves a little between high 13 and 14. Could be me, I’m not electrical, no 16 though. I fired it up and road it for about 2 miles. High gear pinned, slow crawl, climbed hills, sit and idled. Everything worked fine until I shut it off. Start it back up and within 30 sec or so the light goes out or starts blinking. Can switch in and out while riding and sometimes it’ll come on for 30 sec again. And yep, I’ve never missed an old full time 4wd so much. Parts on order. I’ll clean plugs and replace when they arrive. Maybe it’s that simple

 

[retro]

^^^ See fishfiles advice above. ^^^

Good battery and clean connections solve most electrical issues on these bikes. Unless you are very wealthy... in that case its usually OK to throw money at it, rather than diagnose and confirm before buying.

 

[Carolynskii]

I would say since you got battery measurements while the bike thought it was healthy I would take measurements again after it acted up to get confirmation on that rectifier like Retro said as you may have more than one issue.
Appreciate you reporting back because it may help the next person. Welcome to the forum!

 

[Off_Road_Al]

No new parts but an update today that was different. First, I appreciate everyone’s advice, I’ve never seen anything like it. That’s good advice as well about taking a reading when it acts up. I just rode it for nearly 2 hours. It started out flaky as usual. I hooked a 6’ chain drag up to it to drag the field I just disk and when I went from 4wd to 2wd back to 4wd it locked in and stayed the whole time. I drug the field then sprayed fence with a sprayer never shutting it off and it worked fine the whole time. So coincidence...maybe. But under a load it worked fine for a long while. Maybe it is just a connection issue (possible charging issue) and didn’t do my due diligence checking eVery plug.

 

[Carolynskii]

Well there's a very technical explanation for that ........ your bike has lost it's darn mind! Lmao

 

[retro]

Its a connection issue, costs almost nothing to fix. Get yourself some dielectric grease and treat every harness plug pair on the bike. Clean grounds too... and you may have to spray the switches out if it sits out in the rain and weather uncovered. Have fun!

 

[retro]

It sounds like you may have been letting periodic maintenance slip as well. You can find a free copy of the factory service manual from this site and spend a measly $100 on it to catch up.

 

[Off_Road_Al]

No luck yet. Start it up and it’ll will engage for 30 sec or so, sometimes longer. Sometimes when riding it the 4x4 light will go out and it’ll disengage and then come back on and engage with a hard flip of the throttle. Eventually it will start blinking 6 times and not engage until I shut the engine off and restart but then it just does it again.

New battery that charges at 14.5 volts at idle when the light is and is not flashing

Unplugged and cleaned then greased the electrical plugs at the front diff. There are 4 plugs, two green, a gray and a blue. Traced them back to a large gray plug at the top of the steering stem. Also replaced the 4x4 control unit.

I guess I’m looking at ordering another speed sensor? When is acceptable to beat it to death and lite it on fire? Does anyone have any ideas first?