Coolant light question

[dstang97]

UPDATE ON 2ND PAGE




I'm guessing that if the lights ( low coolant and High temp) do not flash when you turn the key they are defective and need to be replaced with new switches right? I already checked the contacts and did a search and only found info on low coolant, but not High temp. I need to fix asap because yesterday I blew a hose at night and it did not warn me.

 

[dstang97]

Anyone?

 

[doghead]

I've never noticed them. I'll go look at mine now.

 

[doghead]

The low coolant light comes on when the key is turned on(before starting).

The temp light lights up when I crank the engine over.

 

[Warthog]

I'm guessing that if the lights ( low coolant and High temp) do not flash when you turn the key they are defective and need to be replaced with new switches right? I already checked the contacts and did a search and only found info on low coolant, but not High temp. I need to fix asap because yesterday I blew a hose at night and it did not warn me.

The High temp will come on in the start position. You can trace dark green circuit 35A & 35B in diagram E-3 and E-4

The low coolant light should light for a few seconds when the key is first turned on as a test. It is controled by the low coolant module. It gets it power from the pink/black circuit 139. Ground is circuit 150. Idiot light Gray circuit 69. And temp sensor yellow/black circuit 68. Diagrams E-3 and E-4


It could be a bad bulb, dirty circuit connectors on the instument cluster, bad/dirty low coolant module in diagram E-3 and E-4 in the TM 9-2320-289-34 manual.

Right click on thumbnail and choose "Open Link in New Window"

 

[dstang97]

Thanks guys

I checked every bulb when I was last in the cluster and cleaned everything, so that is definitely not the problem. I am going to replace both sensors and see what happens. If I was to take the time to diagnose would I be looking for 12v or Ohms at these sending units?

 

[Barrman]

The -10 tells you which light lights up when during the start process. Then, the huge electrical troubleshooting section in the -20 takes you through how to make each light come on for test purposes.

 

[JAsher45]

I had this same problem when i had a head gasket go bad. the temp light never came on cause the engine coolant jacket in the heads filled with air from the cyinders, and over pressurised the radiator. the pressure then caused the radiator to push the coolant out into the overflow.. the only thing i knew was the tattle tale sweet smell of antifreeze hitting the exhaust.

 

[dstang97]

OK did some more researching and found out some stuff I had already known but I'll repeat it for everyone else.

every light should flash when you try to start your truck. that tells you if it is working correctly.

So on the Low coolant sensor it says that you take off the ground and light should go off. Ok make sense but my light never came on. So is that the sensor, module, or a wire touching something its not? I looked, but could not find the answer. It told me to tell a supervisor.

 

[Warthog]

Since you are your own supervisor.........................

You will have to breakout the voltmeter and start checking the circuits.

My first guess will be a bad contact on the circuit board on the intstrument cluster. I have seen many bent/missing/coroded contacts on the clusters I have worked on. Just because the bulb is good, doesn't mean the contacts are making a complete circuit.

Have you removed and cleaned every fuse in the fuse box? Checked the ground wire that attaches above the emergengy brake?

Then I would check for power at the Low Coolant Module.

Checkout these post for an example.

http://www.steelsoldiers.com/electrical/43351-cucv-instrument-cluster-repair.html?highlight=cluster

http://www.steelsoldiers.com/cucv/46054-cucv-instrument-cluster-decoded.html?highlight=cluster

 

[topgun217]

I always tell "doghead" & "warthog"they've always been the right answer men when the tm's say to "tell a supervisor"

 

[dstang97]

Warthog I am having trouble understanding those diagrams. I am not very good at reading those, but 2 months ago I did the cluster repair I bent all wings cleaned with sandpaper, checked all bulbs and contacts so I am 99.9% its not a connection in the cluster. Here is what I found when I went probing around.

At the low coolant module I am getting 12v at Port A and E
I then plugged in the sensor and nothing changed. I do have a m1009 across town that is unmolested so I will snag that module and see what happens, But does this seem Correct?

 

[Barrman]

Did you actually put power to the pins on the gauge cluster and see the light come on? The cluster in the post by Warthog about repair ended up in my truck. I had to pull it to mess with the speedometer. I put it back and some of the lights didn't work. I pulled it again and went through each light with a power source. Lights that worked in the truck didn't on the kitchen table. Lights that worked on the table didn't on the truck. Of course all this use of the big plug on the back caused a few of the contacts to break off. I have gotten pretty good at using super glue to hold them in place while I solder them together.

These trucks are 25 years old or more. Take nothing for granted when it comes to connections and wiring. Check everything by starting at one end of a circuit and go all the way through until you find the problem or reach the other end. Then go through it again.

I had this with my fuel gauge. It was all the way over past full. I followed the -20 and ground the pink wire at the sender. My observer in the truck said the gauge moved when he turned on the key. That means bad sender. I did it again and the gauge didn't move. didn't move any other time I tried it after that. Wart hog told me when I got the truck that it sometimes worked. -20 says replace gauge. I did. No change. I put in another used one and no change. I decided to live with it. A month later I was under the truck checking the brake lines for corrosion. While I was running my hand on the rear line, the pink fuel sender wire fell down on my face. It was chewed through above the rear axle, yet until I moved it. Still was making contact every now and then. Spliced the wire and I have a working fuel gauge.

Check everything, even if you think it should be good because C happened when you did A and B.

 

[dstang97]

Ok the low coolant module was the issue for the low coolant light, now that the light works I have to replace the sending unit.

BUT I replaced the sending unit on the temp gauge and nothing happened. So now I am real lost as what that could be. I took out the light and put a meter to it. I guess the last thing I could check/test the circuit board on the back of the panel right?

 

[rnd-motorsports]

To check to see if the thing works with key on simply pull the wire off the sending unit and ground it same as the collant level it just a ground switch when the temp reaches a sertain level the swicth closes or grounds the wire turning the light on (its the sending unit on the driver front corner of the engine the one on the pass side is for the glow plugs) just for those who will ask witch one is the temp light sender. I like to see the temp so I put gauges in mine mechanicl not electric!

 

[dstang97]

To check to see if the thing works with key on simply pull the wire off the sending unit and ground it same as the collant level it just a ground switch when the temp reaches a sertain level the swicth closes or grounds the wire turning the light on (its the sending unit on the driver front corner of the engine the one on the pass side is for the glow plugs) just for those who will ask witch one is the temp light sender. I like to see the temp so I put gauges in mine mechanicl not electric!

OK low coolant problem is 100% fixed

But still having trouble with the coolant temp. (Brand new sensor) I tried grounding it out and nothing happened. So what you are saying is, there is always power to the coolant light at the dash So I should check for 12v? I can not understand the diagrams.

 

[Warthog]

But still having trouble with the coolant temp. (Brand new sensor) I tried grounding it out and nothing happened. So what you are saying is, there is always power to the coolant light at the dash So I should check for 12v? I can not understand the diagrams.

The way the high temp lamp works is:

With the key on, the pink/black wire (39A) is suppost to be hot (12v). It feeds the idiot lights on the dash. (temp, low coolant, brake and fuel).The power travels thru the bulb to the dark green wire (35B). The green wire passes thru the firewall at the large terminal block and then onto the Coolant tempature switch on the left front head.

The tempature switch is normally open. When the tempature gets to the proper setting the circuit closes and the idiot light turns on.

When you are starting the truck, the ignition switch momentarilly closes the circuit and lights the lamp.

So things to check:

1. fuse
2. bulb
3. firewall connection ( I have seen more and more trucks that needed the connection taken apart and cleaned)
4. terminal at the switch
5. all the wiring involved

 

[rnd-motorsports]

what warthog said If I read it the way he put it he is saying the temp light sender is in the rear on the left side It is on the left side or driverside but the front of the engine. THANKS warthog you answerd before I saw it

 

[87cr250r]

OK low coolant problem is 100% fixed

But still having trouble with the coolant temp. (Brand new sensor) I tried grounding it out and nothing happened. So what you are saying is, there is always power to the coolant light at the dash So I should check for 12v? I can not understand the diagrams.

Well, little bit of symantics here, but your CUCV should not have a coolant temperature sensor. It has a coolant temperature switch. Sensors give an analog output meaning they very based on whatever they are measuring. Switches are either off and on, digital, and well it will only switch on at a prescribed temperature (most likely 230F).

The switch probably has positive power going to it, the light is down stream of it. Once the temperature limit is reached, the switch closes the contact and connects positive power to the light, causing the light to turn on.

 

[Warthog]

what warthog said If I read it the way he put it he is saying the temp light sender is in the rear on the left side It is on the left side or driverside but the front of the engine. THANKS warthog you answerd before I saw it

That is what I get for not proof reading before I hit the Submit Button.

Yes the "switch" is on the left front of the engine.