I've had to clean my sensor off several times over the years. It gets covered in crud and gives erroneous readings. Take it out and clean it first. If that doesn't work, it may be time to replace it.

Jake

 

I'm thinking it's a bad sensor. If so, where's it located and how difficult of a repair / replace job is it for a newbie?

Thoughts? Thanks!

Sensor is in the overflow tank mounted to the firewall.

Check to make sure you have coolant in the overflow tank up to the MIN Cold line after everything cools off. Sometimes after flushing you have to add coolant to the overflow tank a time or two.

 

Try unplugging it and see what happens.

 

Thanks for the posts, guys.

OK - so I inspected the reservoir and it looked nasty inside. It also had about twice the coolant in it than it should have. So I disconnected the 2 bolts and it had a plastic "fin" on the back of it that slid out of a metal holder attached to the firewall. I disconnected the hose from the reservoir and emptied the nasty coolant into a bucket.

It appears someone tried to plug holes in the system using copper at some point and it was caked all over the reservoir. I cleaned it out the best I could.

Then I noticed that the line I disconnected had quite a bit of copper build-up in it, to the point where it looked clogged, or at least mostly clogged. I disconnected the line from the radiator, sprayed it out, cleaned up the reservoir, reattached it, and no warning light so far. Hopefully, that was the issue and now the problem is solved.

NOTE: I did not see anything resembling a sensor ON or IN the reservoir - it was just plastic - no wires or anything else other than the cap itself. Where else could the coolant level sensor be located? Or am I totally missing something?

 

NOTE: I did not see anything resembling a sensor ON or IN the reservoir - it was just plastic - no wires or anything else other than the cap itself. Where else could the coolant level sensor be located? Or am I totally missing something?

This is from the 1994 C/K Truck Manual regarding the Coolant Level Indicator. (Unfortunately we do not have a 1993 manual in the FAQs):

DIESEL ENGINES
The coolant level indicator circuit is shown in figure 7.
Indicator Lamp Will Not Illuminate
1. Turn the ignition switch to the "ON" position.
• If the lamp illuminates, the lamp is OK and the
connector is properly installed on the module. Go
to step 2.
• If the lamp does not illuminate, check the bulb,
socket, and wiring between the socket and the
module connector, as well as the connector on the
module. Replace or repair as required.
2. Turn the ignition switch to the "ON" position and
disconnect the electrical lead at the coolant level
sensor on the radiator.
• If the lamp fails to illuminate, check the wiring
between the coolant level sensor connector and
the module for a short circuit to ground. If the circuit
is OK, replace the module.
Indicator Lamp Remains Illuminated
1. Turn the ignition switch to the "ON" position.
• Check the coolant level. Add coolant if necessary.
• If the lamp remains illuminated, go to step 2.
. Disconnect the electrical lead at the coolant level
sensor on the surge tank and use a jumper wire
and "G" type electrical connector.
• If the lamp does not illuminate, replace the sensor.
• If the lamp remains illuminated, connect the
electrical lead and go to step 3.
. Check for an open circuit between the sensor and
the module.
• If an open circuit is found, repair it.
• If no open circuit is found, replace the module.

The factory manual indicates the sensor is on the radiator in one part of the trouble shooting instructions and on the surge tank later on in the instructions :confuzeld.

So all I can recommend is check the radiator for a sensor with an electrical connector.......

 

Low coolant light.

My truck is a '93 6.5 C2500 and the low coolant sensor is in the passenger side radiator tank. About a foot down from the top. Also, if I'm remembering this correctly, the circuit board fed by the sensor and that controls the low coolant light is behind the ashtray. You'll have to pull out the ashtray assy.

 

Thanks, all. The problem of the warning light seems to be fixed, as it hasn't illuminated in the last 24 hours or so. Let's hope that stays true.

I inspected the radiator and I think I found the sensor - where a few of you mentioned it was - passenger side, about 10 inches down. I took a pic to show you, but I'm not sure how to insert it - it wants me to insert it from a url instead of from my PC. If you can point me in the right direction on how to do this from a url, I'll share the pic on this thread.

Thanks again!

 

93 and older is in the right side radiator end tank.

94+ is in the surge tank on the firewall.

93 and older systems are the "traditional" setups with a cap on the radiator, and a simple one hose overflow tank setup.

94+ runs a "surge tank" setup with no cap on the radiator, and a relatively large feed line "T"ed into the lower radiator hose, and a burp line from the rad to the surge tank, and the pressure cap on the tank.

For folks with the 94+ setup, if you have a 94-96 and your tank is in poor shape with a bad sensor or is leaking, remember to order the tank for a 97+ that came OEM with the K47 airbox, so you have more room, as its just a touch thinner.


TheDauber, if the overflow tank looked like that, imagine what the rest of the system looks like!! I would be flushing the cooling system ASAP, sounds rather sludgy...

 

FWIW... See "Cooling System- Low Coolant Warning Lamp Circuit," page 96 of DB Student handbook.

"One of the end tanks has a fitting for the probe used in a low coolant warning lamp circuit (see Figure 4-12). The monitoring circuit is located in a module mounted behind the instrument cluster.
The low coolant circuit has the ability to detect the absence of liquid in the radiator tank at the probe location and complete the LOW COOLANT warning lamp circuit to alert the vehicle driver (see page 8-37 for more information)."​

 

Good point, GM Guy - will do. Good info, as well. Thanks!

 

HeavyChevy95 - thanks for pointing me to this manual - this will come in handy!