Low Coolant Level Sensor and Buzzer - The Last Thread
 

After disassembling the front harness on the drivers side of my FD (LHD) I was unable to work on it again for over 2 months.

When I could get back to it I found that I had forgotten where a couple wires were supposed to go.
Had one of the connectors not broken off this would have been a no brainer, but...

So, I left these wire exposed, finished the wire re-wrap, filled the radiator, turned the power on.

10 seconds or so later the low coolant buzzer started buzzing.

Now, I was fairly sure the 2 leftover wires were those for the coolant level sensor, but I didn't want to hook them up until I was sure.

If you've ever dealt with low coolant level sensor issues, and have searched here, you will know there aren't any complete threads on the topic, so I am creating one here.

You can find most of this stuff if you search long enough, but it's kind of a pain.

So, here's what I found over the weekend, all in one spot.

1. As shown in the pic, the brown/white wire with the blue tabs is the wire that connects to the coolant level sensor, then goes to connector X12 and on to the CPU.
A shown in the pic, mine has a green extension on it from a repair.

2. The black/red wire in one of the other pics goes directly to the coolant level sensor. This one is kind of of confusing, as it does not appear in the wiring diagram. More on that in a bit.

3. The coolant level sensor is on the front of the thermostat housing. As you can see in the pic, this is a black wire. This black wire goes to the ignition harness, and is routed behind the alternator. Somewhere in the harness the black wire is connected to the black/red wire seen in a previous pic. This change does not appear in the 93 wiring diagram.

4. Grounding the brown/white wire will stop the coolant buzzer. However, when you ground this wire, the buzzer does not immediately stop. It takes 10-15 seconds of keeping the wire grounded before the buzzer stops. Likewise, when connecting the black/red wire to the brown/white wire, it takes 10-15 seconds for the buzzer to stop.

This was kind of had me confused for awhile, as I would ground the brown/white wire to make sure I had the correct wire, but the buzzing would continue. Then I noticed that when turning on the ignition key, it would take 10-15 seconds ( I never timed this) for the buzzer to start. So, I grounded the brown/white wire, and the buzzer would stop. So then I connected the black/red wire to the brown/white wire, left it there, and the buzzer eventually stopped. Success!

If your low coolant buzzer continues, and:

* You've checked the continuity of the wiring
* Grounding the brown/white wire stops the buzzer

In this case it is most likely the sensor needs replaced. I found a number of threads where folks found the sensor was simply bad.

Nice.

Updated the FAQ thread with a link to this thread.

Very helpful consolidation :nod:

good stuff.

i emphasize the part on grounding the wire for 15 seconds to stop and start the buzzing. knowing this stops alot of headache if known before hand.
many people think that the issue is somewhere else because of this. lol

nice write up. does anyone think doing this just to disable the buzzer completely would be a good idea? with someone that regularly checks servicing on their car would it really make a difference?

I wouldn't recommend doing that temporary is one thing but disabling permanantly is a no go in my books.

even if you regularly check you car...things can still happen while driving.

dont disable! just stop the buzzing to wait for new parts to come in

This is a great write up , I've been going crazy finding out why the buzzer wouldn't shut up and just now noticed I have the brown /black wire , disconnected from the red black . now I gotta find it haha

what about second gen?
 

Great writeup but do you happen to have this info for a second gen....'88? I am sure its not the same configuration but I just got the coolant buzzer for first time.

Thanks

Terri

No, I do not have that info.

Ok thanks

Terri

So bringing back an old thread to life.

I have the coolant buzzer issue on my car, searched and read just about every single "Coolant Buzzer" thread available in the world. All say ground the wire out to shut up the buzzer, or there is a bad sensor, or bad wire.

I started my troubleshooting and found a few things wrong, Continuity from the "Black" wire that goes from the water pump sensor to the "Brown/White" wire was not real good. So I repaired both ends of the wire with new connectors, tested continuity, perfect.

Moved on to the "Brown/White" wire, found that the wire at the connector was broken. So I got a new connector, spliced the wire, soldered it to the new connector, tested continuity, and resistance (check in at 0 Ohms indicating a good solder).plugged the wire back in, buzzer lives on...

Now I search around and I find my Oil level sensor is also needing repair, I follow basically the same procedure above. repair connectors, solder wire, test to make sure its a good solder, plug it back in, buzzer lives on.

So lets move on to the "add coolant" portion of the troubleshooting, because that's in all of the threads I find. I get my Lisle funnel, start the car, and let the car get rid of all air bubbles in the system. this goes on for about 90 minutes, just to be sure. checked all coolant levels and buzzer lives on....

At this stage of the game it can only be the sensor right? even though its a brand new water pump assembly in the car with a new sensor, I buy a new sensor anyway. put in the new sensor.... and wait for it... buzzer lives on!!!

So I say screw it, i'm grounding this wire and moving on with my build because I just cant stand that damn thing buzzing all day... so I grab the wire, ground it and.... buzzer lives on!! WTF??!? I ground both the oil level sensor and the coolant level sensor and nothing, buzzing continues without any sign of stopping, and yes I waited the required 20 seconds, heck I grounded it and waited 10 minutes with no change.....
Now I bust out my workshop manual, find the wiring diagram and see where this stupid thing goes into so I can verify that its not broken somewhere. From my understanding, it actually goes into the X-18 harness, behind the instrument cluster. so I pull the cluster and everything is plugged in correctly.

Now i'm stuck, no grounding works all the wiring is repaired and checks out fine, but my buzzer doesn't shut up... the only time I got it to shut up was when I had the cluster out and I left the plug that goes into the cluster that feeds the temp gauge out, when I did that no buzzer, but that more than likely is because the circuit was not complete.... Anyone have any ideas? i'm about to go nuts with this buzzer....

Is there continuity from the black/red wire (#3 in original post) to the sensor?

Did you check continuity between where it’s at on the x-18 harness and in the engine bay to see if the wiring is good throughout the car and engine bay?

what about grounding it straight out of the x-18 plug?

I was thinking of doing this exact thing. though I have been trying to figure out how I'm going to accomplish that feat... my multi meter leads aren't that long...might have to make an extension out of speaker wire that should work. I'm also going to replace the CPU #2, I have a spare here anyway just to see if it makes a difference.

I made an extension for my meter out of wire when I was trying to track down the same type of thing. Worked perfect for it.

Just out out of curiosity, you verified the right connector in the engine bay? I ask because I had a similar issue the other day. I couldn’t get mine to turn off for anything. I was pretty close to stabbing the speaker out under the dash because it was annoying me. I found this thread and started looking for more connectors. Turns out the reason mine was doing it was because I was using the power steering connector. I have P/S and AC in the car still so everything is a tight fit. I found the right connector in the bottom of the engine loom under the ac compressor. There was like 1/2” of wire and the connector coming out of the harness and it was on the bottom of the harness so I couldn’t see it. I just felt around until I got lucky.

replacing th cpu would be the next resort though if you have good continuity from the connector inside to the connector in the engine bay.

Is your low low coolant light on as well?

So I ID'ed the wires coming from the sensor (black with red dots) that go behind the power steering pump so I know that one is the correct one for sure. From all my searching the coolant level sensor wire in the harness is a Brown/White wire which is where the wire from the sensor is plugged into, power steering is Black/Red, Oil level sensor is Blue/Red.

There must be a break in the wire between the engine bay and the dash, or I have a bad CPU #2...

FYI, the low coolant light is NOT on when the buzzer is going off, so perhaps the cluster is at fault... Unless there is something else that makes that stupid buzzer go off that I am not aware of.

Burped it and buzzer went away!
 

===========
We burped the radiator line and the buzzer stopped thankfully!
We

There is definitely no air in my system, as that was part of the troubleshooting process.

Won't hurt to bump anyway
 

bUMP

====

We didn't think there was any air in it either but apparently there was. Might not hurt to bump it anyway.

I have, multiple times... also grounding the wire out didn't work as it should, which means, even if the sensor was working, the buzzer probably would continue either way since the connection back to the system isn't complete somewhere.

Anyone know if the "exhaust heat" light triggers the buzzer too? Haven't been able to track that down yet...

Mine didn’t trigger the buzzer.

have you had a chance to check continuity between the harness side and the plug in the engine?

I have been bogged down with a few other projects and haven't had a chance to keep tracing this thing down. I pulled the middle plug from the CPU #2 so that shuts the buzzer off, but it also takes away all my interior lighting, power mirrors, etc. kind of a pain so I should be getting back to it this week.

I however am starting to think its not the coolant buzzer, as the coolant light never comes on. it is 100% burped and the coolant is full. If I am not mistaken, the oil level sensor, also triggers the buzzer, might be the only two things that trigger it if I remember it correctly.

Probably will buy a new one and replace it on my first oil change, just crossed the 300 mile mark on my brand new engine so breaking it in before the warranty from Mazda runs out. anyway, i'll update the thread once I have this buzzer figured out.

Were you able to resolve your buzzer issue?

I'm helping a friend with a coolant buzzer issue on his 93. In his case, the low coolant light is on, as well as the buzzer beeping.

We checked continuity from the coolant level sensor to the grey chassis connector and confirmed there is no break in the wiring. We grounded the wire at the sensor connector and waited 10-15 secs and the buzzer stopped beeping.

This lead us to replacing the coolant level sensor itself with a new Mazda OEM sensor. After topping off the coolant level and making sure it was above the sensor, we started the car and the buzzer came back on.

We then grounded the wire at the sensor connector again and after 10-15 seconds, the buzzer stopped beeping.

So it appears while there is continuity in the stock wiring, perhaps resistance is too high in a section of wire or the pins have light corrosion/not fully seated affecting the quality of the ground.

We plan on checking resistance next. Any feedback is appreciated.

checking resistance seems a logical next step

Hey, sorry for the late reply. I chased the wire alll the way back to inside the cab, that didn’t lead to a solution unfortunately, and I sold that car shortly after that. It was a mystery that remained unsolved...

resistance would be my next point to look at, you’re on the right track.

Ironically, the buzzer and low coolant light resolved itself this past weekend when my friend started his car again. We did measure resistance from the chassis side connector vs. at the new coolant sensor connector and it was just under 1 ohm, which should be fine.

If the issue appears again, we will dig deeper and report back.

The intermittent issue came back and we then tested continuity from the engine bay to the connector at the gauge cluster. Continuity checked out fine. Low coolant light still on and buzzer still nonstop. We isolated the issue to the cluster.

To test the theory, we then swapped a known good gauge cluster and the light and buzzer went away. Everything worked normally and as expected.

My friend then sent his cluster to Geoff P from Circuit Board Medics and sure enough, there were leaking caps and cold solder joints. Geoff checked the circuit for the buzzer after his repairs and confirmed the issue is resolved.

We are waiting for his cluster to be shipped back and will confirm the fix.

In summary, if the low coolant sensor checks out, and there is continuity in the single wire from this sensor all the way to the connector behind the gauge cluster, then the issue likely exists within the cluster.

TG888,

If the fix was to repair cold solder joints and leaking capacitors then it sounds like the culprit is the Speedo Circuit Board. I'm interested to see what was repaired and replaced.

Geoff suspected the same regarding the Speedo Circuit Board. We'll take photos upon receiving the cluster back. If there are any specific shots that you'd like, let us know.

I've read through your threads on the gauge cluster and CPU2; lots of great information in there. 😁

TG888,

Thanks! I'm glad the speedo board and CPU#2 threads helped you understand their function.

I'm curious to see TR1 (Q1) and TR2 (Q2) and their associated components. They are easily seen at the top-center section of the speedo board (without removing the speedo face).

It's good to hear that a repair was successfully made. Enjoy!

Hey
Thanks for the precious informations in this topic.
Yesterday, after replacing the oil pressure sensor, I had the low coolant and buzzer. I really didn't understand because I knew the coolant level sensor is in the front of the engine, not in the oil filter area... But, thankfully to you guys, I quickly found out this brown/white wire coming out the harness near the oil pressure sensor, that was loose after I struggled changing the pressure sensor in this tiny area.
Made a quick fix and voila !!
Attached below are some pics, may be useful for some newbies like me 😉
https://cimg1.ibsrv.net/gimg/www.rx7...a7bc93604d.jpg
The wire loosed from its plug
https://cimg2.ibsrv.net/gimg/www.rx7...2eb7d7659b.jpg
The quick fix
https://cimg3.ibsrv.net/gimg/www.rx7...629de829f7.jpg
Voila

We finally had time to install his repaired cluster yesterday and here are some photos (the cluster repair fixed his low coolant light and buzzer issue):

https://cimg5.ibsrv.net/gimg/www.rx7...ad7a0f15b9.jpg
https://cimg9.ibsrv.net/gimg/www.rx7...770675229a.jpg
https://cimg5.ibsrv.net/gimg/www.rx7...0e22e3588e.jpg
https://cimg6.ibsrv.net/gimg/www.rx7...77b54817d4.jpg
https://cimg1.ibsrv.net/gimg/www.rx7...96a165ce8d.jpg

Thanks for the update and posted photos. May those repairs last many miles!

What other systems use the same buzzer?



Is that buzzer connected to oil pressure and or oil level sensor? Perhaps another system?


I have a condition where there is no buzzer at idle, and when the engine revs seemingly the buzzer comes on at higher engine loads.


I have isolated the coolant level sensor I think both by grounding it out and as well as putting a 3 ohm resistor in line, with no change. I think the sensor is OK as it is completely disconnected and reacts the same.


Still there is no buzzer when idling, and when a higher rpm is used, seems to activate the buzzer.


Any other systems to check where the buzzer is being activated from?


Pretty certain my oil pressure is good..if not higher than normal...from a pineapple oil mod I did not request. but I can check that if it is a likely cause.

rotarypower101,

This is just a quick note but take a look at the Body Electrical Manual (BEM) for troubleshooting the Body CPU. It receives multiple inputs to sound off the buzzer.

The link here: F100 CPU Post 7 cites the specific Flowcharts to use.

Let us know what you find! Does that help?

P.S. The problem may be tied to the over-rev alarm since you mentioned it happens during higher rpms. And how high of RPMs are we talking?

Not very high RPM/Load, just pulling away, or if cruising and giving it a bit more throttle very mundane amount of change.

It’s a fairly recent phenomena, and I didn’t think much of it, assumed it was the coolant sensor as I have had that issue before if the system is not topped up to the ml…

Since I do not use the vehicle frequently, I went to spend the time to fix it and explore what I thought was going to be a faulty level sensor…unfortunately it is something else ambiguous to me ATM.

If anyone has any advice what to look into from experience or similar symptoms, would really appreciate some thoughts on it.

Can I add any details that might help narrow down and target what might be activating this buzzer?

I Thankfully don’t have very many gremlins in my car, and this is one I would really like to find and step on.



Also does anyone know about the PNW PFC tuning scene? Portland Oregon to be more specific, Need some help finishing up an incomplete Steve Kan tune.

I don't know how significant it is, but is seems to not activate the buzzer below the 2000 RPM range. Can rev and play with throttle (while parked) below 2k with no buzzer, above 2k it activates the buzzer.

My oil pressure gauge is rising with throttle and looks "normal" I have not added an independent gauge to validate yet, nor am I inclined to think that is the issue?

Is it possible it could be a "high over-rev alarm buzzer" that could have some "old hardware" symptom where the activation threshold has been reduced? Similar to those faulty caps that were replaced above?

Is there a way to quickly test for a complete wild guess like that? Might there be a way to disable the "Over-revolution warning alarm"?

Struggling to think of what to contribute the symptoms to, and how to track it down logically.

The high rev buzzer can be adjusted with a knob behind the cluster.
https://www.rx7club.com/2nd-generati...buzzer-590822/

Though, based on what you said, I don't think this knob can 'lose' 6000rpm, unless you manipulated the dash clusters recently.

Also, I may be wrong, but i'd say the high rev buzzer is slightly different than the low coolant or start-up buzzers. I'm really not sure about this, but i'd say it's not the same pitch.

I guess you already verified your coolant level, right? Filled up to the top?
Besides that, I guess there are many sensors that can activate this buzzer, but I've no idea which one here...

No manipulation of the cluster.

BY no means am I asserting this is the issue, completely spitballing based on very little feedback from the car and exploring why I am getting a buzzer out of nowhere that is apparently different and strange to my normal observed operation.



I can easily be wrong, but to my ears it sounds like the “exact same” buzzer that the low coolant warning uses, same pitch and sound. But maybe they use two identical buzzers.



When disconnecting the coolant level sensor, we would expect the buzzer to alarm because of lack of ground/the expected 3 ohm?



My coolant alarm system seems to operate as expected if I understand its feedback and functionality.



I get a ~10sec buzzer if grounded.

I get no buzzer if coolant level sensor plugged in while parked and started

I get a constant buzzer if disconnected or open.


When I rev past 2k range, I get a constant buzzer.



Again want to reiterate, I am not confident that is the issue, but searching for something to grasp at to resolve the issue…strange it would be seemingly RPM based and at a sharp cutoff point, but I was thinking the fluid level “could” change on water pump cycling faster, but seems to Not be the issue if the above is true as I removed it from the system and get the same variable RPM feedback?

Even if I "sneak" up on the RPM slowly, the buzzer seems to alarm at a sharp definite repeatable point in the RPM.

Does anyone know the electrical system enough to postulate how to temporarily strategically disable Only the RPM warning signal to narrow down the causes of this alarm?

What might I be looking for to explore disabling Only this input leaving other functionality alone?

Does anyone know if the FD specifically has a potentiometer to adjust the high rev point? And might there be a thread or post detailing its adjustment someone knows about from seeing it or reading on the topic?

Attachment 746143

Attachment 746144

The buzzer is all the same - it's in CPU#2. There's one buzzer for everything - low oil, low coolant, shift up.

Low oil pressure will NOT cause the buzzer to go off.

The link above about changing the RPM point of the buzzer is on an FC, there's no setting that I know of that will do it on an FD.

It sounds to me that the buzzer is thinking you're at 8000 RPM and it's going off. Either the tach is putting out the wrong thing or the CPU#2 is bad/flaky.

Dale

I would advise not pulling any wires that would temporarily disable the buzzer.

There is no method of adjusting the over-rev buzzer. It is hard-coded in the speedo board.

Before you take any further measurements, take a look at the Body CPU. Inspect it for leaking caps or other potential damage. Do the same with your speedo board. Take some pics on anything that you believe to be suspect. Post them and I could offer some advice.

I'd like to add one more item to inspect: the tachometer.

Take a look at the solder joints along each of the 22 pins on IC1. This may not show much because you would be looking at the top side of the IC chip. The bigger tell would be the back side of the small tach board. The only way to access it would be to remove the tach needle and face. Take a look at Rev counter going crazy Post 2 and download the PDF file. It gives step-by-step directions to remove the tach needle and face without breaking anything.

Because the procedure to remove the tach face is more involved, hold off on that for the moment. You may still inspect the exposed side of the tach board for any potential problems. Let's try to eliminate any problems in the Body CPU and Speedo board first.

How does that plan sound?

I’m having the same issue. I changed the coolant sensor with no change. I will attach a video. This is way quieter than when I started it.

@Bigpopps22,

Welcome to the forum, new member. Show us the problem you have. Then, follow this link that discussed the problem you appear to have.

Alarm Buzzer above 2k RPM

I would guess that you have bad capacitors on the speedometer circuit board (inside the instrument cluster) or similar inside the Body CPU (CPU#2). You can also read more threads that deal with bad capacitors on the speedo board. Do a search with my screen name and the words speedometer and odometer. You may be reading for a while.

Tell us more about your car. Is it stock or list the mods you have installed? Other than replacing the coolant level sensor, what else did you work on under the hood or dash recently? Does your odometer work? Do you have cruise control and if so, does it hunt for a constant speed when set?

I may have to look into this CPU#2 . My odometer recently started disappearing and when it flickers on and off while driving a buzzer goes off and on at the same time. The 2 related?

@wickedywick,

Given your description then follow the link & advise offered in the above post, Post #48. It really sounds like the root of your problem is leaking capacitors in the Speedo board.