Honda CB400 Coolant sensor

[chriss]

Hi Guys,

I'm a new user :)

I would like to ask you a question, I have a Honda CB 400 SF version R (1992). I have a problem with the temp gauge. If is not working. I've bought a new genuine sensor and still did not work. I am sure it is good since I've tested it with the multi meter. The old sensor also worked... I've tried to short the sensor to ground and the gauge needle went up and down as I removed the wire.

I am now aware that the previous owner change the dials (tachometer module) with another. It seems that the new dials have some sort of different resistance that does not match with the sensor.

Do you have any idea how can I go around this issue?

Thanks in advance,

Chris

[SevenThreeSeven]

I guess you'd have to do some research to discover exactly which model/version of the CB400 gauge binnacle the bike's prior owner installed, then do more research to find the correct "genuine" water temp sensor that model/version required. If you can match those two things they should give good readings.

Although it would come as a surprise to me if you found that Honda used different temperature sensors on such similar bikes, but you never know do you?

Did you check the input voltage to the temp gauge? The temperature sensor is just a "thermistor" which is an electrical resistor whose resistance is greatly reduced by heating, so you want to make sure the gauge has good/correct voltage input for the temperature sensor to act upon.

Sounds like you've already done a bit of a test on the gauge, maybe accidentally, if I'm reading your post correctly. Because connecting the terminal of the temperature gauge where the temperature sensor is normally connected directly to a ground (i.e. the bike's battery negative terminal) will simulate the temperature sensor having reached its full (hottest) end of the temperature range. At the hot end of its temperature range the temperature sensor completely grounds the gauge, flowing the maximum 12volt current through it which will cause full-scale deflection (end of the range, full overheat reading).

[chriss]

Hi,

Thanks for your reply.

Yesterday I've dismantled the dials but unfortunately it has no model. :S 99% its a model that could be found on ebay (china ones)
In the link below you can view the gauge I have.

http://www.ebay.com/itm/GAUGES-Speedome ... c1&vxp=mtr

Unfortunately I do not have the wiring diagram of such device.

Yes, when I ground the wire connected to the sensor it makes a full scale deflection and the pointer goes to the H point.

I think I will try to figure out what is the exact voltage coming in the gauge (probably 12V) and check the wiring.

If the problem still persist I think I should go for an original gauge rather than the china one :)

thanks once again for help,

Chris

[Albertus]

Hi Chris,

Try doing a hot water test and check the sensor's output voltage.

Al