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2015 Hino 258 RPM run away

redline808

Well-Known Member
Joined
Jul 4, 2007
Messages
101
Location
Hawaii
Thanks for the update. Glad you figured it out. I’m interested to find out if your fuel economy increases.
FYI. That was not the fix.....Did the same thing in the next rain. Turns out water leaked onto the harness plug on the passenger side. That plug was associated with the TPS and pedal. Dried the plug and used dielectric grease on all connections. Good to go now.
 

redline808

Well-Known Member
Joined
Jul 4, 2007
Messages
101
Location
Hawaii
Hi redline808 do you know what all you unplugged? If you don’t mind me asking I’m having the same problem right now
Under the dash on the passenger side is a black box. That is the bulk head and all the harness connections are in there. The main harness enters from the top of the box from behind the dash. water leaks from the windshield and onto the harness, then runs down the wires and soaks the connectors. The largest connector, which is also the worst one to access is likely flooded and is causing the runaway RPM issue. I noted water also get into the TCM that is behind the plastic dash panel on the passenger side. The one that all your passengers grab onto thinking its a handle and it pulls the whole dash panel off..... I'm sure everyone has had that happen LOL. Anyways the water starts corrosion on the TCM board. Hope this helps you!
 

MikeMike258

New Member
Joined
Apr 24, 2023
Messages
3
Location
Florida
Under the dash on the passenger side is a black box. That is the bulk head and all the harness connections are in there. The main harness enters from the top of the box from behind the dash. water leaks from the windshield and onto the harness, then runs down the wires and soaks the connectors. The largest connector, which is also the worst one to access is likely flooded and is causing the runaway RPM issue. I noted water also get into the TCM that is behind the plastic dash panel on the passenger side. The one that all your passengers grab onto thinking its a handle and it pulls the whole dash panel off..... I'm sure everyone has had that happen LOL. Anyways the water starts corrosion on the TCM board. Hope this helps you!
Do you know name for which harness it is or the the name of the large connector that you said could be soaked I’m calling around for it and I’m getting asked which harness and connector thanks for you help
 

redline808

Well-Known Member
Joined
Jul 4, 2007
Messages
101
Location
Hawaii
Do you know name for which harness it is or the the name of the large connector that you said could be soaked I’m calling around for it and I’m getting asked which harness and connector thanks for you help
I don't quite understand who your calling and for what your calling them for?
 

Shorty_ntd

New Member
Joined
Feb 7, 2024
Messages
1
Location
Australia
Hey guys I’ve been hunting a similar issue with my FM Hino 2004 with the 1J motor. After multiple attempts I’ve finally found my issue. The heater core had a leak and coolant was dripping on the main wiring harness connectors. The plug in the picture is for an external hand throttle for a garbage truck and it had coolant residue in the plug causing a resistance between the red and green wire making the engine rev up at idle. Hope this info helps someone IMG_3998.jpeg
 
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