Hey everyone, I've read some threads on this issue with others and tried several things but my issue persists. I have a 1991 FC Non-turbo. If I put the key into the accessory position but don't turn the car on after a bit a loud alarm plays from the instrument cluster accompanied by an 'ADD COOLANT' light on the HUD (I'm assuming the buzzer is warning me of the same thing the light is). The alarm doesn't go away when I turn the car on and doesn't seem to go away even if I leave it to warm up. If I turn the car on before the alarm begins it will still happen. I've tried the obvious, adding coolant, but when I take the cap off there is coolant right up to it. On my car the fill 'neck' is on the radiator towards the center (it has previously come to my attention that the radiator on this car may be from an s4. This is because there is an unused sensor at the bottom of it which others have said is something an s4 uses but wouldn't be on an s5). This seemed like a natural issue because where the upper radiator hose connects to the top of the engine is higher than this point...so how could air ever get out of there? I tried jacking the front of the car up in an effort to get the fill cap to be the highest point on the cooling system and was able to get some bubbles but the alarm persists. I have coolant in the reservoir.

I could really use tips on how to troubleshoot this. Do I have a problem with the thermostat, air in the system, or something else? Thanks.

 

Might be obvious, but you didn't mention it so to confirm: is your coolant fill sensor plugged in? It's the plug on top of the radiator in the middle. If it's unplugged the coolant buzzer will go off.

 

Have you removed the water level sensor from the top center of the radiator and tested it? If the sensor is in air for about 10 seconds the buzzer goes off.

There is a bleed plug after the filler neck, right near the angled section on the radiator to bleed air because of that odd bend it has and might be trapping air.

The heater core has a valve that only opens when the heat is on, and closes, preventing any hot water to enter the core. Have you started the car with heat on to make sure that this has pushed any air bubbles out of it too, as the bubbles would join near the bottom of the radiator and would then when you turn the car off, would flow backwards up the radiator and create the pocket where the sensor sits, again with that bend preventing it from reaching the filler neck?

 

I appreciate the obvious things. Even an experience professional can miss them and I'm far from one of those. Your question brings up a question on my end which easily could be the beginning of solving this problem....what sensor? My radiator certainly has no sensor at the top. It has a sensor on the bottom driver's side corner of it that was never connected to anything since I purchased the vehicle. I asked some Rx-7 guys about it and they said it's because the radiator is from an s4 and so the sensor is not connected to anything because my s5 has nothing to connect it to. Here's some pictures to make this all a bit easier.


Sensor at driver's side bottom of radiator that has led others to say the radiator is from an s4

To of radiator. No sensor but notice to the passenger side of the pressure cap something seems to have been filled in.

Just in case it comes up, this is the neck going into the engine block. Seen picks where there is a fill cap here which I don't have.

 

I'm starting to think someone previously had removed said sensor and filled in the location where it is supposed to be on the radiator....another way the previous owner has somewhat screwed me. Honestly I feel stupid for only now noticing what seems now like a pretty obvious JB weld fill in or something. What throws me off now is.....it didn't scream at me before when I first purchased the vehicle but it's definitely been like this since then.

 

Yeah, looks like someone removed the sensor in the very center and filled it in with some kind of gunk.

Maybe they had the wire that originally went to the sensor and just grounded to something and it fell off.

 

Must be it. I did have the radiator off and did a lot of other work, I might have at some point accidentally undone whatever it is they did to silence the alarm. So, I'll need a new radiator and a new sensor but can anyone tell me where I can look to find the connection for the sensor that is supposed to be there?

 

The coolant level sensor is a long, single brown wire with a black connector, I believe. Check the wire I circled below, looks like it might be it. The previous owner probably grounded it to turn the buzzer off.



The radiator appears to be from an automatic, it looks like it has connections for the trans cooler near the sensor you pointed out on the bottom.

 

I forgot to mention that others have said the same. This has a manual trans though. Safe to say this radiator is not original to the car. Worth noting that I don't get coolant coming out of those.

As to the wire you might be onto something it's not connected to anything and clearly was not spliced by the factory:


Notice the color of the wire is green with a red stripe? So I found this connector:



Despite it seeming to be a two pin, it has only one wire going into it but it's also green with a red stripe. I'm not sure what to do with this information but here's a little more intel I gathered. Using a circuit detector (just lights up when there is current) I found that there is current when I attached the wire you circled to 'positive' on the battery but not ground and grounding this wire didn't turn off the alarm. For the record, I'm not looking for a quick fix and fully intend to get the proper sensor hooked up, but if I can replicate the quick fix then I can know that this wire is what is supposed to go to the sensor.

 

Neither of those is it. After checking the wiring diagram (http://wright-here.net/files/manuals...ingDiagram.pdf) my memory was off a bit, it's a brown wire with a white stripe. Definitely a single-pin connector. It may come out of the main harness near the passenger headlight connections, but it's been a while since I've looked at it.

 

Ah yes I have found it, brown, white stripe coming out of the harness. It clearly was at least attempted to be grounded to a bolt going into the frame near the headlight. Again I'm somewhat confused as to why I have not always been plagued by this issue. It was still connected to it's ground. However, using a circuit detector I found that where it's connected is not actually grounded. But, it had to have been at some point or I would have always had this issue....it doesn't make a lot of sense to me. It seems that the ground is just not great but it sometimes works I guess? Never-the-less I at least can now get the sensor and install it on a new radiator and that should hopefully take care of the issue. Thanks everyone I'll keep this updated on whether I find success.

 

Correct. Also in reference to the unused tube fittings, sometimes aftermarket radiators (which the one you have most definitely is) come with that regardless of whether you're getting it for a manual or automatic vehicle. That way they only have to stock one part.

S5 has that type of neck, so you're fine. S4 is the one that has a fill cap that you're describing.

 

Something else I just noticed. Your overflow line goes to the pressure cap on the radiator. What do you have on the pressure cap on the filler on the engine? That water is going to be hotter there and more pressure due to heat, where does that water go to because I do not see a T into that overflow tank?

 

Cancel.

 

I don't have a filler on the engine (see third picture I posted on my second message on this thread). As was clarified for me by mR.dnA , s5's have no such filler cap. So the line from the pressure cap on the radiator is the only one going to the overflow.

 

So a bit of an update. I did get a sensor and new radiator which I have yet to install but something that concerns me is that the alarm is not actually silenced by grounding the wire we located. Based on the diagram and the way it was clearly attempted to be grounded out by the previous owner it seems clear to me that this is the correct wire but grounding it doesn't silence the alarm and so I'm worried there is a deeper issue. I've gone as far as to directly connect the wire to the negative terminal of the battery with no luck. In addition, using a circuit detector there is no current running through this wire even when I connect the other side to the negative terminal of the battery. Is this normal? I'll admit I don't really understand how the sensor works with just one wire going to it....is it grounding itself through the radiator? The radiator is isolated from the battery so that doesn't really make sense to me. I'm moving forward and I'll still replace the radiator, wire up the sensor, and install it and maybe my worries are unfounded but based on the fact that I don't get current through the wire and grounding it doesn't silence the alarm I have a hunch this won't completely solve my problem.

If it doesn't there could be a break in the circuit somewhere else. This may somewhat explain why I didn't have the problem until now. I'm in the midst working in the interior and have since removed the dashboard and most of the components which plug into the wiring harness there. I have the HUD that has the add coolant light attached, as well as the gauge cluster (from which the alarm sound seems to come), and obviously the ECU is still plugged in but not much else. Car starts and runs though beyond the alarm. Could there be something I have disconnected that is breaking the circuit to the sensor wire?

 

When the radiator is full, the sensor is grounded via the (conductive) coolant to the engine block. When it's low, the sensor is exposed to (insulating) air, so the sensor is ungrounded and the alarm goes off.

Unground the wire and check if it has voltage to it - black end of a multimeter to ground, red to the wire. I would expect it would have 12V; if the voltage reading floats around or reads something nonsensical, there is likely a break in the circuit.

The diagram shows 2 connectors between the dash and level sensor: the round one that plugs directly into the cluster, and a rectangular connector (X21) which connects to the main harness above the steering column. If both of those are plugged in, the wire might simply be broken somewhere.

 

That's actually really cool the way it grounds to the coolant. Electrical stuff I didn't know but now that you explain it, that makes as much sense as grounding to the frame. It all leads to the negative terminal of the battery in some way. New things learned aside, I have done what you suggested and unfortunately the multimeter did not read even close to 12V (though it did react to the difference between key on and off). I'm sifting through the wiring diagram myself. I've had some electrical classes that give me a small foundation that allows me to slowly follow what the diagrams are telling me so I'll see if I find anything. But it seems that if something was unplugged that shouldn't be that the HUD and the gauge cluster wouldn't work properly either.

 

What did the volt meter read? If it was jumping around randomly it likely means the wire isn't connected to anything. If your interior is mostly out, you could unplug the gauge cluster and check for continuity between the pin in the round connector (number C-01, same wire color, brown/white, page C1 of wiring diagram) and the sensor connector. That would tell you definitively if the wire is broken.

 

When I turn the key to accessory it jumps from 0v to about .2v and wanders around that number a bit. So not much at all but I thought it worth mentioning that it does react. I performed the continuity test you mentioned and it does have continuity which I think is good news. That means I need to look 'earlier' in the wiring for the issue. If the Brown and white wire is going "out" to the sensor, in theory some wire goes "in" to the gauge cluster that is related to this as well right? If I'm reading the diagram right, there is a wire that comes from the "Warnings & Auto Clock" (which is the device I've been calling the HUD) which goes into this. It says it's a Brown and Black wire going into the same connector C-01. I should check for continuity between that point and where it goes into the HUD which is on C-07 in the "K" pin I think.

 

Okay I've confirmed continuity between C-01 and the coolant level sensor wire. I've also confirmed continuity between C-01 and C-07 via the Brown/Black wire. So the signal can get from the HUD to the Instrument cluster, and from the IC to the sensor. But from what I'm understanding in the diagram there isn't an exclusive wire to follow before the HUD. Power comes into the HUD through the ignition switch and then goes to various sensors. So then I could be looking at either an issue with the HUD or the IC right? In that case the HUD would be my suspect as it already has an issue with it's clock. The clock seems to have an unreliable connection, flickering on and off from time to time, resetting each time it does. It wasn't super important so I haven't given it much thought until now. I think I can check for continuity of the HUD. The wire for the coolant sensor comes out of pin K from what the diagram is telling me, and power for the HUD goes in through pin G. so I should be able to continuity test those two pins which I tried and there isn't continuity. I checked K against all the other pins just in case and got the same result. So am I right in concluding I have an issue with the HUD itself or am I understanding electronics, continuity tests, or the diagram wrong?

 

To my understanding, the buzzer and "add coolant" light are controlled by the circuit in the dash; it turns both on when it senses the sensor is no longer grounded. I don't think a faulty idiot cluster would cause the buzzer to ring, since the warning light takes signal from the dash, not the other way around.

Since there is a diode on one side of the light, it won't register continuity between pins G and K. However, if you use the (+) probe on pin G and the (-) probe on pin K, there should be a finite resistance value. The diodes I have on hand measure about 600 ohms but I'm not sure how they compare to the ones Mazda used 30 years ago. The clock flicker is a known issue, if you're comfortable with an iron you can reflow the solder joints as discussed here.

Does the add coolant light stay on when you ground the sensor? The buzzer also sounds for low oil and the shift indicator, is your oil light on?

 

I feel like I'm going insane a bit here. I'm pretty confident that the light does stay on when the sensor is grounded and I don't get any other indicators. That being said, I can't verify that at the moment because it's not doing it anymore. Inexplicably, both the light and alarm are no longer present at the moment when the car is running or in accessory position. I'd love this to be a victorious moment but it's not, I don't feel like the problem is actually solved because the sensor isn't even plugged in or grounded right now so the alarm should be happening but it's not. I don't know what to say on this problem now. since we're talking about other indicators I'll mention I have a check engine light on that flashes only the code 11 to me which is "Intake Air Thermosensor (Engine) - Intake air fixed at 68F" but I don't think it's related and I haven't gotten into that one yet. Only mentioning it incase it's somehow related because I'm at a complete loss at this point.

 

Okay, the "add coolant" light and the alarm do both come on at the same time (both seem to fade in sometimes). But what I've found is when I mess with the white connector on the back of the instrument cluster the alarm will stop, at least for a bit. Wiggling it also sometimes causes the gauges to momentarily loose connection. As a temporary solution I simply jiggle that whenever the buzzer goes off but this often only stops it for like ten seconds before it returns and we can go back an forth for a few minutes before it stops for a longer period of time.

Now that I've been getting into the electrical system I may need to start a new thread because I've noticed a bunch of odd little things that all seem related to the wiring.