Hino temp gauge problem

The temp gauge in our hino 2004 GH1J is playigng up. Generally, when you have the air con on and things are warming up (big load, up a hill) the temp gauge climbs right up, switch the air con fan off and the gauge falls back down to normal temps. Behaves fine until you turn the air con on. I'm thinking they share an earth which has gone bad. But having problems finding it. I thought I could just add another earth, but can't work out which wire.

Hino emailed me the wiring diagram for the sender and gauge (combo meter) but it does't show any earths. Is any one able to decipher it or know where I'd find the earth?

Hmm i may have rushed things here, I was obsessing over an earth but just assumed it was sending a 24v to the gauge and then reading the resistance, actually it's looking at the resistance to earth isn't it... So it might be one of those connections to fuse 19 or 3

Wedgy
Gudday M8

Sum big beasties have factory set
to increase coolin wen AC iz on
dunno ifn u're lorry haz a variable speed fan or doodadd to increase cool n wen AC iz on

Jist guessin outside the square
otherz may kno bettr
:lol: :lol:
cya

well it's a recent problem, hasn't always been like this. Also doesn't have to be ac, can just be heater fan...

Crook Contact or and Earth

Swishy wrote: Crook Contact or and Earth

completely agree, it's finding them I'm struggling with. It's not short of a wire or two behind the dash and I need to find where to look...

Sounds to me that you might have a crook fuze or connection supplying 24V to the AC or Heater Fans.
I f this is the case, when you have a reduced voltage supplying the gauge, the reading will be affected, ie , lower voltage with the same current running through the gauge changes the resistance, ie, more resistance = higher temp reading.
Hope this helps
Cheers
Alistair

I sent you a PM Wedgie.

Your problem reminds me of almost every Austoft cane harvester and Powerhaul I have ever driven, as you'd have to turn off all your lights and air con to get an accurate fuel level reading.

Bitsa wrote: Sounds to me that you might have a crook fuze or connection supplying 24V to the AC or Heater Fans.
I f this is the case, when you have a reduced voltage supplying the gauge, the reading will be affected, ie , lower voltage with the same current running through the gauge changes the resistance, ie, more resistance = higher temp reading.
Hope this helps
Cheers
Alistair

Thanks - yeah this seems the theme. It's coming over today so I'm going to have at the fuse box and dash. First will check if they share fuses...

dieseldog wrote: I sent you a PM Wedgie.

Your problem reminds me of almost every Austoft cane harvester and Powerhaul I have ever driven, as you'd have to turn off all your lights and air con to get an accurate fuel level reading.

Thanks DD, good to know you've come across a similar problem. Now you mention lights I think someone might have mentioned the lights triggered the fault the other day!

From what I can work out, the CPU is supplied from fuse 19. I'm assuming the CPU is looking at the current flowing through the temperature sensor, and supplying a current to the gauge that is proportional to the sensor current. I can't see where the air con circuit ties into these circuits as these are low current control/supervisory circuits.

Since the air con compressor and coolant temperature sensor are both earthed on the engine block, I would check the block to chassis earth strap.