92 TRX350 Fourtrax Oil Temp Light - Honda ATV Forum
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post #1 of 16 (permalink) Old 05-28-2019, 10:02 PM Thread Starter
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92 TRX350 Fourtrax Oil Temp Light

Hi folks, finally found a beautiful old tank in fantastic shape. Just working out a few kinks. One is the oil temp light...it does not come on during the test when turning key on initially. Fan works when the lead to oil temp sensor is grounded. Is this a big deal? Reverse light does not come on briefly initially either but comes on when reverse is engaged.

I have searched all the threads repeatedly and didn’t find an answer to this one.

Anybody have any insight!?

Thanks.
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post #2 of 16 (permalink) Old 05-28-2019, 11:35 PM
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Both the fan motor and the oil temp light should come on when you ground the sensor wire. If both come on the fan control unit is good. Next test the resistance through the oil temp sensor using a decent multimeter. It should measure between 9.5k ohms and 10.5k ohms at about 68 degrees F (20 degrees C). If the sensor measures out of that range by more than 500 ohms it needs replacing. If its within range, ride it! Got any pics of your TRX350?
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post #3 of 16 (permalink) Old 05-29-2019, 06:40 AM
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Coolness, a 92 Foreman!
Does the light come on at all?
The service manual steps you through a diagnostics and explains how to get the fan and light to come on by grounding that lead.
If the light doesn’t come on you will have to check the bulb.

Use a flat blade screwdriver to gently dislodge two tabs in the Honda dash insert—gently! Don’t break it.
Underneath there are two screws—remove them and roll the dash over and rearward. This will expose the harness—gently work the friction fit connector from the dash insert. The socket may be dirty or the bulb burned or prongs rusty.

I had all three on mine, plus the PO had a very heavy rack on the front fender that pushed the fender down onto the dash harness–chafed every wire on the bundle. I also used dielectric grease on the bulb seats and the rubber so they would pop into the sockets easier

Notice I referenced the 89 TRX350 parts listing because the later models aren’t listed. Supposedly the 90-93 TRX350 were built in Japan using 89 parts and were not exported to US because Honda began building TRX300 in the US.
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Last edited by Goober; 05-29-2019 at 06:56 AM.
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post #4 of 16 (permalink) Old 05-29-2019, 07:49 AM Thread Starter
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Thanks guys, shoulda mentioned that I put a new thermal sensor in it already, checked the bulb and it doesn’t appear to be burnt. Guess I am wondering if the control unit could cause it. I’ve never seen the light come on at anytime. Have taken the bike on some pretty good rides and have not seen the fan come on either...I’ve read that they need to get pretty hit but just trying to make sure the system is working...if the light never comes on!

Retro, I’ll post up some pics later!
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post #5 of 16 (permalink) Old 05-29-2019, 10:30 AM
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I pasted the troubleshooting flow chart from the service manual, section 20. You can find a copy of the FSM linked from @Goober's sig if you need one.
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post #6 of 16 (permalink) Old 05-29-2019, 10:53 AM
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Take off the inner fenders.

Left side make sure all your fan control unit connections are clean and tight. Esp (Blue) Bu and Blue/Red wires. Pull off right side panel and check Blue wire not disconnected

Right side check the red connector to see if there’s any chafing on the dash harness. Blue/red

Your fuel gauge work? Neutral and Reverse lights? The other wires connected to the light is the Black/Brown fed by the lights fuse so if your guage works check for power at the light bulb.

My experience is real easy to unintentionally disco the connectors on the FCU and under the right side panel

Lol ok i bet the prongs are bad on the bulb connector—swap known good bulb. Otherwise loose Bu/r on the FCU!!
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Last edited by Goober; 05-29-2019 at 11:08 AM.
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post #7 of 16 (permalink) Old 05-29-2019, 05:55 PM
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I believe it's possible a bad or intermittent FSU can cause this issue, in addition to the suggestions listed by everyone above. I have 5-6 FSU's and I came across one that would occasionally not trigger the oil light briefly with the key. Swapped it out and problem went away. I suppose it's just as likely there was a poor connection and swapping units corrected that condition. I'll probably run into it again, as I can't bring myself to throw any of them away just yet.
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post #8 of 16 (permalink) Old 05-29-2019, 07:03 PM
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Quote:
Originally Posted by Duck0fDeath View Post
I believe it's possible a bad or intermittent FSU can cause this issue, in addition to the suggestions listed by everyone above. I have 5-6 FSU's and I came across one that would occasionally not trigger the oil light briefly with the key. Swapped it out and problem went away. I suppose it's just as likely there was a poor connection and swapping units corrected that condition. I'll probably run into it again, as I can't bring myself to throw any of them away just yet.
Hey Duck have you considered heating the bad one? I had an FCU from a TRX300, wouldn’t give me an oil light. Heated it in a 200 degree oven for three full hours—no smell no melting—and let it cool. It works now.
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post #9 of 16 (permalink) Old 05-29-2019, 08:47 PM Thread Starter
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Quote:
Originally Posted by Goober View Post
Take off the inner fenders.

Left side make sure all your fan control unit connections are clean and tight. Esp (Blue) Bu and Blue/Red wires. Pull off right side panel and check Blue wire not disconnected

Right side check the red connector to see if there’s any chafing on the dash harness. Blue/red

Your fuel gauge work? Neutral and Reverse lights? The other wires connected to the light is the Black/Brown fed by the lights fuse so if your guage works check for power at the light bulb.

My experience is real easy to unintentionally disco the connectors on the FCU and under the right side panel

Lol ok i bet the prongs are bad on the bulb connector—swap known good bulb. Otherwise loose Bu/r on the FCU!!
I’ll check those out, thanks bud. There is no fuel gauge on this machine. It’s a canadian fourtrax trx350 not the foreman. The reverse light doesn’t go through the test sequence with the key either but works when gearerd into reverse.
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post #10 of 16 (permalink) Old 05-29-2019, 08:51 PM Thread Starter
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Quote:
Originally Posted by Goober View Post
Quote:
Originally Posted by Duck0fDeath View Post
I believe it's possible a bad or intermittent FSU can cause this issue, in addition to the suggestions listed by everyone above. I have 5-6 FSU's and I came across one that would occasionally not trigger the oil light briefly with the key. Swapped it out and problem went away. I suppose it's just as likely there was a poor connection and swapping units corrected that condition. I'll probably run into it again, as I can't bring myself to throw any of them away just yet.
Hey Duck have you considered heating the bad one? I had an FCU from a TRX300, wouldn’t give me an oil light. Heated it in a 200 degree oven for three full hours–no smell no melting–and let it cool. It works now.
Thats interesting idea...what does heating it do!?
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