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Discussion Starter · #1 ·
If you'll look at my new member introduction, you can see the details about my new toy. EVERYTHING works as new, except, of course, the pesky LOW COOLANT lamp. The malfunction on mine is a little different, but I just wanted to describe how it acts...I'm sure it needs to be replaced.

The light operates normally when starting out cold and even when the car warms up to temperature. Never comes on other than the bulb check when starting the car. The strange thing is if you shut down the car when at temp, the light comes on and stays on when re-started. Let her cool down, light is back to normal...hence, I guess I need to replace it.

I was wondering if it could be due to Dex-Cool. Although when delivered new to the first owner in 1994 it had the green stuff in it (Dex didn't come out until 1996 model year), he changed it over to Dex-Cool for unknown reasons. I know there are all sorts of opinions about Dex that I don't want to get started here, but it makes me wonder if I should go back to the original green when I replace the sensor. Opinions?
 

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Examine the water pump weep hole for leakage.
 

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Here is a theory that comes to mind...After running warm the coolant vents back into overflow bottle to just below sensor level. After cooldown vacuum present in the system draws coolant back to the radiator to a level just over sensor level. Sensor works as advertised. Just a thought.
 

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Discussion Starter · #5 ·
Here is a theory that comes to mind...After running warm the coolant vents back into overflow bottle to just below sensor level. After cooldown vacuum present in the system draws coolant back to the radiator to a level just over sensor level. Sensor works as advertised. Just a thought.
I suppose that could be...

Anyway, I just installed a brand new sensor...now I get no light at all even at key on bulb check before starting. ARRRRGGGG!!!! Stupid me didn't bother to check the new sensor dry before installing it which would have required re-installing/removing the battery again, so I didn't bother...figured heck, it's brand new...it will work....NOT. It's a simple job, just a big PIA.

I now know and understand why people just say F... it and leave it unplugged. I'm just one of those types that wants everything to work as they should on my cars. The old one was pretty dirty...I'm going to try to clean it and re-install it again tomorrow after I (and the engine) cool down. :mad:
 

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If you cannged it and now it doesn't work make sure you inspect the electrical connection as well.
 

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Discussion Starter · #7 ·
If you cannged it and now it doesn't work make sure you inspect the electrical connection as well.
Yes I will tomorrow. I'll connect up the battery with battery cables to the battery connectors so I won't have to pull it in out while troubleshooting...

I wonder if I could just hook up a battery charger to the battery connections....
 

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Yes I will tomorrow. I'll connect up the battery with battery cables to the battery connectors so I won't have to pull it in out while troubleshooting...

I wonder if I could just hook up a battery charger to the battery connections....
I wouldn't do that. Some chargers put out too much voltage under a light load or no load.

These sensors go bad by leaking coolant inside after a few years. The type of coolant is not important. You can test the lamp by shorting the two terminals in the sensor connector with it unplugged.
 

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Discussion Starter · #9 ·
I wouldn't do that. Some chargers put out too much voltage under a light load or no load.

These sensors go bad by leaking coolant inside after a few years. The type of coolant is not important. You can test the lamp by shorting the two terminals in the sensor connector with it unplugged.
Yeah, I was sort of afraid to try that. After I thought about it, the jumper cables won't work either since it's a side post threaded battery. Back and forth we go with the battery I suppose....:mad:
 

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I keep a couple of side post adapters in the car's tool kit, just for that issue.

 

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I don't mean to hijack the thread but I have a similar issue but with the low oil light. Definitely has enough oil in there-every once and a while it comes on and stays on for the remainder of the drive. I also have the low coolant light come on more often, once again coolant is topped off. Curios to know what you find out.
 

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Discussion Starter · #13 · (Edited)
I don't mean to hijack the thread but I have a similar issue but with the low oil light. Definitely has enough oil in there-every once and a while it comes on and stays on for the remainder of the drive. I also have the low coolant light come on more often, once again coolant is topped off. Curios to know what you find out.
Well, let me calm down for a few...I'm so f...ing p..sed off right now, I could eat nails...

OK, a little better now...but not much :mad:. So I went down to O'Reilly's to get the battery charging posts...decided to go ahead and get ANOTHER Low Coolant Sensor (Their brand is BWD...lifetime warranty....hrumpppp) after returning the AutoZone HQRP POS that didn't work. Well guess what? The POS BWD brand doesn't work right EITHER. :mad: And yes, I checked the wiring connector per the "Official" Carline 1994 Firebird service manual. The bulb check is simply to short across the two terminals on the plug...if the low coolant light illuminates at key on bulb check and after starting stays on, the plug/harness is working correctly. These sensors simply close an internal switch when no liquid is present at the sensor on the switch (which is same effectively as shorting the connection) to illuminate the light.

The problem with BOTH aftermarket coolant level sensors it that NEITHER one lights the LOW COOLANT light when plugged in dry (key on bulb check)...UNLIKE the factory sensor which DOES turn the light on dry. They CANNOT be working correctly if they do not illuminate the Low Coolant Light when dry as a bone. So...I cleaned up the old original factory sensor and tested it. Light came on dry, stayed on dry after starting the engine, light off with engine running and sensor submerged in a cup of water. So, I said OK, maybe since I cleaned it up, it will not come on after the engine is shut down at operating temp. and re-started....NOT....AGAIN...SAME PROBLEM :mad:.

I would spring for the ONE HUNDRED THIRTEEN BUCKS for the factory switch if I knew it would work...but stealerships will NOT refund electrical parts...even if unused. And I'm not ABOUT to pay $40 bucks an hour to let them do such a simple thing, then if it don't work, have them ALSO tell me that it is working...just because the light is off. THAT'S NOT HOW THESE SENSORS WORK. Look it up in the simple owner's manual...the light is SUPPOSED to come on at startup, then go out. GGGRRRRRRRRR!!!!!!!!!!!!!!!!!!!:mad::mad::mad::mad:.

I guess I may join the rank and file and just unplug the damned thing like everyone else that can't get it solved.
 

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I bought from Rock Auto (for '95 Z28 M6)
AIRTEX / WELLS 5S1449 (SU1302) Coolant Level Sensor (9026.10.2990) £ 23.64

approx 36 dollars

Worked for me.

Mitch
 

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Discussion Starter · #15 ·
I bought from Rock Auto (for '95 Z28 M6)
AIRTEX / WELLS 5S1449 (SU1302) Coolant Level Sensor (9026.10.2990) £ 23.64

approx 36 dollars

Worked for me.

Mitch
Thanks, Mitch, appreciate that. Just to be sure before I order it...does your LOW COOLANT lamp illuminate at key on and go out after starting?
 

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There are a few issues with your understanding of this function and the circuitry.

First, the sensor must be in the metal radiator (with the radiator grounded to the engine through the coolant) or in a metal can with the can connected to chassis ground. That provides the reference for the sensor to work. Without the ground, nothing happens. Just putting it into water alone will not work.

Second, the thing that causes the lamp to light at ignition on time, is the RAP module, not the sensor. Typically, the light is dimmer at that time than in operation with low coolant.

Third, the sensor does not simply short the two wires together. It produces a signal that pulses to ground. Then the RAP module latches the line fully on when it sees the pulses. Shorting the wires to test the lamp works, but it is not the perfect method and doesn't test the RAP module.

One thing that might screw this up is to have an LED in the low coolant lamp position, since the sensor needs voltage to operate.
 

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It could be that the RAP module isn't working or not working properly. Even with the RAP module disconnected, the lamp should light dimly with the sensor connected and in a dry condition. Try that in the dark. I suppose that the newer sensors may not provide enough current to light the lamp by themselves but the old one might, due to a different design.

To test the RAP module, just unplug the sensor and switch on the ignition. The lamp should light for a few seconds. If it doesn't, the module is defective or the wire to it is broken or loose.

The fact that your old sensor lights the bulb may only indicate that it is shorted/defective.
 

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Discussion Starter · #18 ·
It could be that the RAP module isn't working or not working properly. Even with the RAP module disconnected, the lamp should light dimly with the sensor connected and in a dry condition. Try that in the dark. I suppose that the newer sensors may not provide enough current to light the lamp by themselves but the old one might, due to a different design.

To test the RAP module, just unplug the sensor and switch on the ignition. The lamp should light for a few seconds. If it doesn't, the module is defective or the wire to it is broken or loose.

The fact that your old sensor lights the bulb may only indicate that it is shorted/defective.
Firstly, my car doesn't have a RAP module...it does not have power windows, locks, or mirrors....here is the RPO sticker:



Secondly, with all due respect, I must beg to differ about testing the sensor and the way its wiring works, unless you can show me where I'm going wrong here. There is no ground between the exterior body of the sensor...the hole in the radiator where the sensor fits is plastic...in addition, the rubber o-rings sealing it would insulate from grounding even if the mounting hole WERE metal. The wire clip that holds it in can't be the ground either since it's not connected to anything electrically anyway.

Here's a link showing how to test the sensor:

I want to ohm out my coolant level sensor and replace it if

and the diagram showing how to test it from that page here:



As you can see, there is no external ground to the body of the sensor to test it. Where am I going wrong?
 

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1. If you don't have a RAP module, then you do have a Cooling Level latching module, which is the same latching parts as within the RAP. Check the service manual page 8A-81-3 and note the entry about having the AU3 option.

2. Obviously you haven't fully tested the sensor, as have I. It will not work without the ground reference for the probe. The engine and metal internal parts serve as the ground in the car. The coolant (or just water) serves as the electrolyte. The signal I posted is the one I captured while developing a useful test. Without the can grounded, the sensor did not function. I am an electrical engineer with over 40 years experience in the field.

 

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Discussion Starter · #20 ·
1. If you don't have a RAP module, then you do have a Cooling Level latching module, which is the same latching parts as within the RAP. Check the service manual page 8A-81-3 and note the entry about having the AU3 option.

2. Obviously you haven't fully tested the sensor, as have I. It will not work without the ground reference for the probe. The engine and metal internal parts serve as the ground in the car. The coolant (or just water) serves as the electrolyte. The signal I posted is the one I captured while developing a useful test. Without the can grounded, the sensor did not function. I am an electrical engineer with over 40 years experience in the field.

My apologies, I certainly did not intend to slight your knowledge...I'm just trying to understand this extremely frustrating problem (believe me, my patience is REALLY short right now), and really appreciate your help, no doubt, and just going by the information (or misinformation) that I've cobbled together.

So please tell me...where would the Coolant Level Latching Module be located on the vehicle and how would I test/replace it?
 
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