Temperature Gauge or Coolant Temp Sensor for the Gauge?

[bizzaro]

So my temperature gauge stopped working the other day.  Now the gauge is mostly pegged (stuck) high, but I can get it to drop to pegged(stuck) low when the key is off by rapping the side of my knee pad.  This suggests to me, it is the gauge, and not the sensor . The gauge is no longer available by the way.  But can someone point me to how you would test the sensor? And, or how test the gauge? I would  assume I could test the resistance of the sensor and it should have a cold value as well as increasing with values the coolant temps rise?  I have done an extensive search. Nothing comes up. 
Thanks in advance.

[rbm]

The gauge probably has a short circuit somewhere between the temp sensor and the gauge that needs to be taken care of.  It's not the gauge, most probably.  First try to remove the gauge from its metal enclosure and see if it still acts up.  If it continues to peg, there is most likely a short circuit to ground in the cabling, most likely at the temperature sensor in the water pump area.  Disconnect the gauge from its harness connector and test for resistance reading between the Black wire and ground.  If you read near 0 ohms, the short is confirmed in the wiring.  Check the sensor.  There is a 1/4" female spade connector that contacts the temp sensor's hot terminal (the other end is grounded through the water pump body).  Check that it is not touching a part of the motorcycle frame.

[Blue]

The circuit for that gauge is not fused and has been known to spark bikebque.

[bizzaro]

Robert, I knew you would have an answer!  Blue, thanks for the heads up on potential wire roast.  Smells bad and tastes worse.

Thanks,Guys.  Will check it out when I get a chance. For now I will just unplug it.  I suspected a short.  But thought I would inquire anyway. 

[Scott_]

The circuit for that gauge is not fused and has been known to spark bikebque.

I don't think so....  According to the BMW wiring schematics, the power feed for the gauges is as follows..... Battery -> fuse #5 -> engine electronics relay(Motronic relay) -> fuse #1 -> gauges.

[bizzaro]

Thanks Scott. Just to be on the safe side, I will disconnect it.  I was looking at my Clymer schematic for the 94K11LT wiring trying to trace the temp gauge and sensor etc. last night looking for possible issues. I am pretty sure it is s short, as RPM has suggested, and I suspected.

[rbm]

Additional instruments power comes from Fuse #1.  See the Schematic:  https://drive.google.com/open?id=0B3UPbNZRyr1rVGVrWngyaHBkZjA
9940 = gas gauge
9945 = water temp
B9562 = water temp sensor
F9200 = Fuse #1

[bizzaro]

There doesn't appear to be a short. I get no continuity between the black and ground.  I get .4 ohms at the  four pin connector between the black and ground.  And .4 ohms at the sensor between the grounding nut/coolant plug and center spade connector.  Is that the correct value for a cool engine? I am guessing/thinking it is the sensor.  If I test the same connection(the coolant plug/ground and it's center spade connector with a hot engine the ohms value should change? Correct?

Is there a way to hook up the gauge to simulate the sensor?

Thanks...................................

Oh, and Blue, I did manage to blow fuse #5 fiddling around. In my owners manual it is says the #5 fuse is the motronic, which covers many connections.  Just so ya know.

[rbm]

What you've just described is a shorted temp sensor.  If there is 0.4 Ohms between the tip of the sensor and its body, then the sensor is a dead short.  Explains the pegged needle.  The resistance should be about 2000 Ohms at room temperature, according to the below chart.


If the gauge was working fine one minute and failing the next, then it was a catastrophic failure not characteristic of a weakening NTC resistor.  Try isolating the components to help identify the bad one.  Take off the spade connector and measure sensor resistance again.  if it reads 2000 Ohms, then the problem is your lead wire between the spade connector and 4-pin plug.  Carefully examine the entire length of the wire. Maybe its a small stray strand from a wire that is contacting the frame.  Maybe the insulation has worn off somewhere.   It disappears behind  the HES cover so maybe the wire has chaffed  over time with the heat of the engine.  Maybe it's time to replace the wire.  Try running a new wire temporarily to the gauge from the sensor to verify the suspected cause.

[bizzaro]

 rbm.   Thanks. Yep. Pretty sure it is the sensor.  I get different values with hot and cold engine when I check the resistance, but it is always in the decimal range.   I may just ride out the season with the temperature gauge as is.  This weather can't go on much longer here in Vermont.  The riding season should end shortly.  Aren't the cooling fan and the overheating temp warning light from the stand pipe sensor, and not the temperature gauge sensor anyway?  Hmm, on upon reconsidering that, it is probably the other way around? The stand pipe sensor is probably "just" for the motronic and fuel injecton input?

The graph for the stand pipe coolant sensor for the fuel injection is not the same as the graph you show here for the temp. gauge is it?  I am going to be checking that when the riding season ends  That is one of the things on my long list of things that need attention on my bike this Winter. 

Thanks again for your help. 
Bizz

[Laitch]

This weather can't go on much longer here in Vermont.  The riding season should end shortly. 

Listen up, Swami! Confine your predictions to MegaMillions. I'm enjoying this weather up here! If it's a sign of the End Times, I'm ok with attending them in a T-shirt.
 :hehehe

[bizzaro]

Laitch, we can't know for sure what is to come now that the Weekly World News has closed it's doors some years past.  They had connections with science and prophets far beyond this world..............................(I think they had Nostradamus's phone number!)   now predicting the future is just a crap shoot!

[billday]

If the gauge was working fine one minute and failing the next, then it was a catastrophic failure.

Let's try to keep things in perspective. It's an inconvenience, sure . . . but a catastrophe?

[Laitch]

. . . we can't know for sure what is to come now that the Weekly World News has closed it's doors some years past. . .

  :tinhat2 WWN—Gone is the citizen's bastion of information untainted by corporate greed.  RIP   
I guess our only choice now is RT. :giggles

[The Mighty Gryphon]

  :tinhat2 WWN—Gone is the citizen's bastion of information untainted by corporate greed.  RIP   
I guess our only choice now is RT. :giggles

Agreed.  I'm convinced that the closing of my only source of news of the world by the Global Elites is part of a plot to hide their plans for global domination.  With the closing of WWN I am deeply concerned for the welfare of Batboy.  Has anyone heard anything about him lately.

[bizzaro]

Not to worry.  When WWN shut it's doors and Batboy was out of work. He moved to Shanghai and got a job at McDonalds! 
(guess this thread is seriously off the rails!) Oh well. My thighs are a pretty accurate temperature gauge anyway! :hehehe