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Temperature Gauge Not Working, Doesn't Move At All


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#1 Big Tom

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Posted 01 April 2009 - 11:32 AM

Hopefully this isn't a repeat of a past question(s), I did a search and didn't seem to come up with much of anything so I thought I'd post and hopefully get some help.


The truck runs fine but the temperature gauge never moves. I'm not sure how this is wired and I've read some places there are 2 sensors one for the computer and one for the gauge itself? Seems odd to me but that's why I'm here.

How can I go about troubleshooting this issue? Where is the coolant sensor located? Is there a way I can test the gauge itself ie if the sensor outputs 0-5V or 0-12V or something can I remove the wire and hooking up a power supply inject the voltage to see if the guage moves properly on the dash? And the reverse, can I run the motor and check the voltage on the output of the sensor to determine if it's faulty?

#2 kuhl_530

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Posted 01 April 2009 - 11:46 AM

Definately sounds like a coolant temp sensor. The sensor for the guage is usually located around your thermostat/water outlet. What year/make/model/engine size is your truck, I can give you a part number and price. Generally speaking they are inexpensive.
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95 K1500 XC Z71
5.7L TBI
3" body lift 33x12.5 mastercraft courser MT
K&N cold air intake
MSD blaster coil, wires, cap and rotor

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SGT. KUHL, USAR

#3 Zembonez

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Posted 01 April 2009 - 12:00 PM

You can tell if the gauge is bad by grounding the lead to the temp sensor. When the circuit is grounded it should peg the gauge. Don't connect power to it. It works by varying the resistence to the ground side of the circuit.

Sorry but I don't know the exact location on the sensor but I'd look for one somewhere near the thermostat housing.

Edited by Zembonez, 01 April 2009 - 12:02 PM.

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#4 Big Tom

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Posted 01 April 2009 - 01:42 PM

Definately sounds like a coolant temp sensor. The sensor for the guage is usually located around your thermostat/water outlet. What year/make/model/engine size is your truck, I can give you a part number and price. Generally speaking they are inexpensive.



It says in the topic description, 1993 Sierra 1500 5.7L TBI 4x4, I'm assuming it'll just be a bad sensor since it's an older truck with quite alot of miles, but I'm here at work and planning a fishing trip that'll take this old girl 1500+ miles round trip so I'd really like to get it working before I leave so figured might as well get as much info before I go home and tear into it :thumbs:


Zembonez: Thanks for the tip, I had heard somewhere about how to test the guage but completely forgot about grounding the wire, so tonight I'll try it (after I find the sensor) and see if it pegs.

Edited by Big Tom, 01 April 2009 - 01:44 PM.


#5 Big Tom

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Posted 01 April 2009 - 07:22 PM

Between the 2 front cylinders, drivers side, little connector with a green wire sticking out of it. Popped off the connector, put a wire in the end and touched it to ground and turned on the key and needle moved to hot.

So yeah, that was easy! Been living without temp sensor for quite sometime now, didn't really care to much until the thought of the long trip ahead came about

Now I just have to get the replacement sensor and hopefully I'm back in business. Next... locating resistor board for the fan control... or hardwiring the fan to simply be on/off whichever is easier :thumbs:

#6 Big Tom

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Posted 01 April 2009 - 07:24 PM

Between the 2 front cylinders, drivers side, little connector with a green wire sticking out of it. Popped off the connector, put a wire in the end and touched it to ground and turned on the key and needle moved to hot.

So yeah, that was easy! Been living without temp sensor for quite sometime now, didn't really care to much until the thought of the long trip ahead came about

Now I just have to get the replacement sensor and hopefully I'm back in business. Next... locating resistor board for the fan control... or hardwiring the fan to simply be on/off whichever is easier :thumbs:

#7 Mike G

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Posted 02 April 2009 - 09:00 AM

Between the 2 front cylinders, drivers side, little connector with a green wire sticking out of it.

Next... locating resistor board for the fan control... or hardwiring the fan to simply be on/off whichever is easier :D


Yep, that's the one.

What is wrong with your fan? Presuming it's the fan for the heater control, could be that you need a new control head. These are pretty well known for going out. I put one in mine a few years back and life was good again. I think it was like $125, but I'm aging and the memory is getting shorter....
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#8 Big Tom

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Posted 02 April 2009 - 09:22 AM

What is wrong with your fan? Presuming it's the fan for the heater control, could be that you need a new control head. These are pretty well known for going out. I put one in mine a few years back and life was good again. I think it was like $125, but I'm aging and the memory is getting shorter....
--Mike



Mike,

Should likely start a new topic but meh we'll use this one. Fan worked great when I bought the truck, then high quit and by quit I mean low/med worked but if you switched it over to high it'd smell like burning electronics, so I started researching about the problem and read a few places mentioning some resistor board that often goes then after awhile low/med completely quit. I pulled out the fan awhile back and hooked power straight up to it and it still worked so it was put on the to do list then shortly after forgot about, much like the temp sensor.

I probably should get it fixed properly but if the bill is much over a $100 I think I'll just hardwire a switch :D

It's a good truck but paid only $1K for it (or about $750 for the Americans reading this) but I don't hardly use the thing so can't justify putting alot of cash into minor repairs, especially since I'm planning to drive the truck into the ground! If I was thinking of selling, I think I'd need to splurge on proper fixes :D

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#9 kuhl_530

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Posted 02 April 2009 - 10:12 AM

I found the temp sensor for ya. It's made by a company called 'standard'. They offer two lines, the first being the higher quality runs $25.19, part number tx3. The second is more of an 'economy' line, part number tx3t costs $12.99.

There are three major components of a blower motor system. You have the switch, the resistor (controls fan speed) and the fan itself. If one speed doesn't work, but the rest do, it's a resistor problem. If only off and fast work, it's a resistor problem. If you have no power at all, it could be either your switch, or motor, the motor usually being the cheaper of the two to replace. In your case, it's almost the same. The motor costs $36 with the wheel or $23 without (just take the wheel off the original and put on the new motor). The resistor costs $25
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95 K1500 XC Z71
5.7L TBI
3" body lift 33x12.5 mastercraft courser MT
K&N cold air intake
MSD blaster coil, wires, cap and rotor

------------------------------------------

SGT. KUHL, USAR

#10 Big Tom

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Posted 02 April 2009 - 04:56 PM

I found the temp sensor for ya. It's made by a company called 'standard'. They offer two lines, the first being the higher quality runs $25.19, part number tx3. The second is more of an 'economy' line, part number tx3t costs $12.99.

There are three major components of a blower motor system. You have the switch, the resistor (controls fan speed) and the fan itself. If one speed doesn't work, but the rest do, it's a resistor problem. If only off and fast work, it's a resistor problem. If you have no power at all, it could be either your switch, or motor, the motor usually being the cheaper of the two to replace. In your case, it's almost the same. The motor costs $36 with the wheel or $23 without (just take the wheel off the original and put on the new motor). The resistor costs $25



Thanks for the heads up on the part, I called the local wholesalers nearby (farming family, have an account) and they have one regular $34 but wholesale price of about $18.50 so I'll get the wife to pick it up on the way through. Not sure if it's the good one or the cheapie, but for under $20 if it moves the gauge I'm a happy camper.

Speaking of which, I want to send the sensor with the wife to make sure the one she picks up is the right one ie size/connector etc so I'm assuming when I remove it from the block alot of coolant will be coming out, any idea how much? I think when I bought it they mentioned they'd flushed out the cooling system so likely I'll be reusing the coolant but I'm not sure if I should try draining the rad first or just pull out the sensor. ie I'll need a clean container, will there be a gallon or two or five? Is there any proper steps to removing the sensor or should I just drain the rad, unscrew the sensor, pop in the new one and refill the system? Should I use any thread sealer when I install the new sensor or just some tephlon tape or nothing at all?

With the blower motor, where is the resitor board located and what does it look like? Someone should make a how-to with pictures and everything because it seems like a pretty comon problem. I'm wondering if I perhaps blew a fuse or something with it because like I said at first everything worked, then high died, and now everything is dead. I'll maybe tear into it tonight and see what I can find out, would be really nice having it working again. So I'm thinking I should try the fan again, likely straight to the battery and see if it still works, maybe it's siezing up and causing to much current flow and cooked the board?

How can you test the switch? This truck has the digital temp display but if I remember (been awhile since I drove the truck) you can hear clicking sounds when you switch between low/med/high, so would there be a set of relays somewhere in the system also?

#11 kuhl_530

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Posted 02 April 2009 - 06:45 PM

when i go to work tomorrow, I'll pull up a picture of the resistor and post it for you, but i'm not exactly sure where it is located on your truck. If you smelled something burning when it was on high, i would venture to say that you have a bad wire(s), but that's just a guess on my part. It would still be a wise decision to check them and make sure you're not shorting, or it could cause a fire under your dash. There are no relays, just the temp/fan control switch, the resistor and the motor. The clicking could be the switch working, and it's losing power between it and the motor, but again, just an educated guess. I would venture to say that the motor seizing would NOT cause an increase in electrical flow. Think of your wires as a river and your motor as a dam. The dam can only flow so much water down river, and if it stops, so does the water, unless the water finds a faster way down river (which would be like a short) and then it floods the river below the dam and drowns everyone out (unrestricted flow of electricity and a fire) . lol crude analogy, but it works
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95 K1500 XC Z71
5.7L TBI
3" body lift 33x12.5 mastercraft courser MT
K&N cold air intake
MSD blaster coil, wires, cap and rotor

------------------------------------------

SGT. KUHL, USAR

#12 kuhl_530

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Posted 03 April 2009 - 08:05 AM

Blower motor resistor is a standard part number ru61 and runs retail about $29.

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95 K1500 XC Z71
5.7L TBI
3" body lift 33x12.5 mastercraft courser MT
K&N cold air intake
MSD blaster coil, wires, cap and rotor

------------------------------------------

SGT. KUHL, USAR

#13 Big Tom

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Posted 03 April 2009 - 10:15 AM

If you smelled something burning when it was on high, i would venture to say that you have a bad wire(s), but that's just a guess on my part. It would still be a wise decision to check them and make sure you're not shorting, or it could cause a fire under your dash. There are no relays, just the temp/fan control switch, the resistor and the motor. The clicking could be the switch working, and it's losing power between it and the motor, but again, just an educated guess. I would venture to say that the motor seizing would NOT cause an increase in electrical flow. Think of your wires as a river and your motor as a dam. The dam can only flow so much water down river, and if it stops, so does the water, unless the water finds a faster way down river (which would be like a short) and then it floods the river below the dam and drowns everyone out (unrestricted flow of electricity and a fire) . lol crude analogy, but it works


Thanks alot for the picture of the resistor board, kindof neat to see the guts of one and hopefully now I have an idea what I'm looking for I can find it. I'm assuming installed it would have a cover over those coils? Either way, when I get the chance I'll take a look.

I popped out the temp sensor last night, took the easy way out and just threw a few pails under the truck and let it drain out. Probably less then a gallon of coolant came out (didn't actually measure but fairly certain) so that's all good. Hopefully pop the new one in this weekend when the wife brings it home and I'll have a working temp again!

I did smell something burning when setting it to high, so I would assume like you a good run through of all the wiring is in order to make sure there isn't a short/burning cables under the dash. Wouldn't be good if someone borrowed the truck or whatever and didn't know not to set it to high and burned up the truck!

And I do like your analogy, but I'm sorry to say it doesn't work. I'm a electronic technologist at a power plant and work with Electricians and Mechanics daily, and we constantly have DC or AC motors trip overload breakers, 7/10 times we send in the mechanics and the bearings are shot causing the motor to draw to much current. Replace bearings and grease the motor, away it goes drawing the proper amount of current. A siezed motor will act pretty much exactly like a dead short if I recall from school. It's kindof like you have your truck set on cruise and are chugging along on a nice flat surface, optimal conditions. Then you start to climb up a hill, you don't loose any speed but your engine and tranny are working harder now to maintain that speed and drawing more fuel to try and keep running. If you climb a even bigger hill (ie more resistance) again, you'll use more fuel and put more strain on everything trying to keep that same speed. For a motor, the more resistance, the harder it works, the more energy it pulls be it fuel or electricity.

Either way, to me it makes sense that likely the motor is on it's way out, pulling to much current and burning out the electronics. Would also explain the large pile of blower motor issues people post on here, alot mention the board/switch is toast but they plug the fan directly to the battery and it spins fine... battery can put out hundreds of amps of juice, electronics can't pass that much current and fry. Also explains why some posts people mention they replaced all the electronics, worked great for a few months then blew up again!

Anywho, this weekend I'll hopefully get some ambition and start pulling things apart to try and find out what's making the burning smell, and hopefully get things working again fan wise. But really thanks for all the help guys, it makes things alot quicker/easier when you have at least some heads up what to look for an expect instead of hours away from the family tinkering on the old truck.

#14 kuhl_530

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Posted 03 April 2009 - 10:26 AM

And I do like your analogy, but I'm sorry to say it doesn't work. I'm a electronic technologist at a power plant and work with Electricians and Mechanics daily, and we constantly have DC or AC motors trip overload breakers, 7/10 times we send in the mechanics and the bearings are shot causing the motor to draw to much current. Replace bearings and grease the motor, away it goes drawing the proper amount of current. A siezed motor will act pretty much exactly like a dead short if I recall from school. It's kindof like you have your truck set on cruise and are chugging along on a nice flat surface, optimal conditions. Then you start to climb up a hill, you don't loose any speed but your engine and tranny are working harder now to maintain that speed and drawing more fuel to try and keep running. If you climb a even bigger hill (ie more resistance) again, you'll use more fuel and put more strain on everything trying to keep that same speed. For a motor, the more resistance, the harder it works, the more energy it pulls be it fuel or electricity.


haha well sorry about the incorrect analogy, I guess i misunderstood how that stuff works, but great information for future reference! Make a post when all is done and let us know how it went. Good luck!
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95 K1500 XC Z71
5.7L TBI
3" body lift 33x12.5 mastercraft courser MT
K&N cold air intake
MSD blaster coil, wires, cap and rotor

------------------------------------------

SGT. KUHL, USAR

#15 Big Tom

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Posted 04 April 2009 - 08:05 AM

Well that was unexpected.


Ok, so I took out the glovebox, 4 quick little screws, then unclipped and removed the silver computer on the very right side, this gave me a over the top look at the fan. Also directly behind the glovebox was 3 relays, and when I selected low/med/high I could hear and feel them clicking! So not sure if I have an older model or what but I guess my circuit has relays, to me this makes somewhat sense since being a digital dash they would provide the low output signal triggering the beefier relays that would act like a switch.

Anyway, so now I see these relays, still no resistor board though so I'm following some wires and looking around when I notice a purple wire dangling... strange... look at the back of the fan there is a black wire connect but nothing else... move the foam cover around and in one of the holes there is the other end of the connector... plug the purple wire back into the fan and try it out and now I have all three settings and no burning smell???

So, not sure what to make of that. I mean I could understand if the purple wire came loose loosing the low/med settings I had before, but why is the high setting now working and there isn't any smell??

Needless to say, the dash will remain ripped apart until I get the new temp sensor installed and I can start the truck and drive around for awhile with the fan running full tilt. Maybe after a few hours to ripping around and no burning I'll put it all back together and hope for the best!




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