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42,885 miles on my '88 FC with 13B, and I've suddenly entered 'coolant level sensor hell'.
Without reason (overflow tank at proper level, coolant FULL at sensor hole, radiator cap, and thermostat cap), low coolant level warning and continuous buzzer on startup.
Bizarre coolant level sensing system! Never seen one on any make of car/truck/tractor,...
Mazda helped me get one of the "few remaining" new coolant level sensors and replacement did not change the situation. If I'm reading the schematic correctly, all this damn sensor does is show the coolant level unit a ground (or partial ground,...through the coolant path to the engine ground, I assume). Does anyone know different?
I expect to start testing the old and new sensors, by grounding their tip, with engine running (per my Hayne's Manual) to see if that stops the buzzer/warning light, but with what I've seen so far, I expect no change,...unless my brand new Mazda coolant level sensor is bad!
But this worries me about repeated starts, without warmup. It's been a couple of months since last drive (and everything was perfect!), and it's been cold started twice without warmup. Testing sensors requires engine running.
Any advice, folks, before I screw it up? I'd like to keep this near new, 30 year old car,
happy!
Thanks, Todd.
Mine started doing the exact same thing. I've properly burped the system and ensure the level sensor is submerged in fluid. I have NOT replaced my sensor yet. I currently have the wire grounded to the airbox bolt that goes into chassis(ground) and the buzzer of death stopped.
Let me know what you find, mine is most likely the level sensor...
Cool! I really appreciate the response, M!
Because of the lack of mileage on this car, I really want to not mess anything up. I'd been fearful of directly grounding the sensor's wire to stop the 'buzzer of death' (Navy electronics training,...). Gosh, does the 'low coolant level' warning go out too?
Last trip was ~40 miles total, to get it's belts changed by Mazda FOR THE VERY FIRST TIME! I just figured nothing had been spent on the car yet, why not splurge? Fluid check prior to, and after, was perfect. No fluid on the ground, and I find fluid TO THE TOP at every entry into the system. Never leaked before and I have no evidence of leaking now. Not even coolant consumption,...
I'll warm this 13B up first! It's December in Colorado!! I can ignore the warning and buzzer long enough to get it comfortably fast idling! Then I'll get out and let it run for a bit,...Once it's warmed I'll start testing sensors,...my old one first.
Schematic seems to show that the sensors have variable resistance. Anyone know what range that might be, in Ohms?
I'd like to keep this 13B running perfectly!
Thank you! Todd.
That particular sensor is just a ground. There is no resistance reference for it.
If you can eliminate the buzzer by grounding the harness side, but it buzzes when connected to the sensor (and the coolant is full, no bubble - which definitely happens with aftermarket radiators, but yours is OEM) then the sensor needs to be replaced.
The "official" check IIRC was to remove the sensor, reconnect it to the harness, and ground the tip of the sensor itself with ignition in the ON position. Buzzer turns off, sensor OK. Buzzer continues, sensor bad. (edit: engine doesn't need to be hot or anything)
Thanks! I find my old sensor to have no resistance. Yes, the entire car is OEM. I hope to check sensors tomorrow/soon.
I'll have to check to see if grounding the end of the sensor wire turns off the warning light and buzzer.
I JUST replaced my original sensor with a new Mazda part because I thought that was the problem,...
Not being used to troubleshooting my RX-7, I'm a little unsure, but I don't think that the buzzer will sound until after the engine is started. I think that's when the warning light shows up,...after all other warning lights disappear. I can run the engine with the new sensor in place while I check the old sensor, and visa versa.
I think I'll make a visual inspection of engine ground also, despite my engine being spotless,...
I'd sure like to fix this, rather than bypass,...you can see why:
Todd.
I know grounding the wire that goes to the sensor works to disable the buzzer and the light on a S5. I imagine the S4 is the same since physical sensor is the same only the plug is different. I would ground the connector for the short term. If that stops the buzzer you'll at least know your wiring back to the ECU is good. Then you can warm it up like you want before you check sensors or even drive it if you like.
Thanks, Dak! With your feedback, and mR. dnA's (and the fact that I find no resistance in my old sensor), I'm pretty well convinced that I can ground the sensor wire without damaging the in-dash warning unit. I'd guess that the coolant level unit portion of it has malfunctioned,...I'll have to see if I can do anything about that later on,...at least I can safely warm it up and drive it.
And thanks, mR. dnA! Since it's all original and with such low mileage, it should be kept this way. My father bought it new in Fort Collins, CO in 1988, and I was finally able to snag it away after he got too big to get in and out! It still has it's original bra, top, and all the purchasing paperwork, etc,...
Still single digit temps right now, so nothing has changed with my car's situation, but with a little deduction, I'm NOT hopeful,...
I have coolant FULL to the top at the sensor opening, at the radiator cap, and at the thermostat housing cap. So I do NOT have a coolant level issue.
My removed 1988 factory coolant level sensor has no resistance, which is what a new sensor should read. And my new sensor has not improved the situation.
I suspect that grounding the sensor wire is NOT going to satisfy the electronic control unit, and I predict that I will still have a continuous buzzer and 'add coolant' warning light.
Temps are supposed to warm in the next week, so I'll see if a ground will work. I suspect I'll be asking how to remove/repair the ECU in the dash soon,...this is gonna suck!
Todd.
Yup! I'm screwed!
Problem must be in the 'clock and warning light' unit in the dash. Grounding the coolant sensor wire does nothing,...continuous buzzer and 'Add Coolant' light.
Unless you guys know better, I'm going to pursue pulling the 'clock and warning light' unit from the dash.
I'll have to contact the closest Mazda dealership to see if they know what I can do to solve this problem. I don't seem to be getting any more feedback here.
Perhaps I'm posting the wrong section,...is there a better area to post this in?
Thanks, Todd.
Doesn't mean you're screwed, just means there is a lot of studying to be done. Have a look at some of my last posts on finding/fixing electrical gremlins. Could be anything. You might have a capacitor failed into a closed circuit or something. Won't know till you study. I'm trying to study the wiring diagrams to find different places for you to test to narrow down the location of the issue. It may be in the unit itself, but won't know until some studying is to be done. Your car looks gorgeous, but she is not a spring chicken. The electronics on these cars have well been used past their designed lifetime, so this type of troubleshooting is going to become more commonplace. I'll get back to you with some ideas once I've done some studying.
I'd download the FSM if you haven't already and start looking over the wiring diagram for that circuit. I don't know what controls that since I've never had a problem with it. May or may not be in the clock but the FSM should show it. These cars are known to have flaky solder joints so that could be the culprit.
I have never had the need for a shop manual for this car, until now. But the e-diagrams in the Hayne's that I've had ever since I bought the car, show the entire coolant sensor (and buzzer) wiring to be within the 'clock and warning light' unit on the dash.
Do you know of a link to the FSM for my '88 convertible? Or should I just rely on googling? Thanks!
I'll begin checking solder joints in the 'clock and warning light' wire,...I was going to check continuity once I had the back of the unit exposed.
Sounds like I'm posting in the right area! Thanks Dak! I sure appreciate the posts!
Todd.
The FSM manual copies I usually use are from rotaryheads.com. Others on the forum prefer foxed.ca as well. Sometimes there are typos/mistakes, so checking both is usually not a bad idea, especially with any sensors/electronics. There have been misprints.
Part of the delay is probably everybody getting back from Christmas.
Here's some information I was able to put together from what I found on the rotaryheads . I have color coded and attached the relevant pages to help you trace the wiring. From what I have found, it seems most likely you are having a premature grounding condition like the others have posted. Since you have both the buzzer and coolant light going off, the failure is most likely associated with a positive output wire from the instrument cluster grounding out. There are other options to try as well, which I will detail after this one. When the add coolant warning is working properly, it is supposed to ground the coolant level sensor to the chassis, with positive voltage flowing supplied from the ignition via the buzzer and coolant level unit (both in gauge cluster), and warning light (from dash). The intersection of these three is at the coolant level unit within the gauge cluster, and follows a single output to the sensor. If unplugging the sensor did not stop the buzzer or warning light, then both are grounding out elsewhere to complete the circuit. The first place to check would be from the Brown coolant output wire in the harness behind the gauge cluster (color coded orange) and see if it grounds out. If it does, then you will know somewhere in that line has failed. If not there are two other options. The buzzer is associated with 3 circuits; the coolant level (Blue No. 1), oil level (Blue No. 3), and tachometer redline (Blue No. 2). If the coolant level circuit is ok, the next failure points are also dependent on diode failure (green arrows) thus allowing for stray current.
Diode failure dependent conditions:
The next nearest ground comes from the oil level sensor. If your oil level circuit has grounded out, the buzzer should go off and show the low oil level on the indicator light. The warning light circuit would have to be severed for a grounding condition to not show the low oil light.
The final ground is through the tachometer. When you are in a redline condition, the gauge grounds the buzzer circuit to indicate that you need to quit being silly. This circuit works independently of the shift indicator light if the diagram is correct. These two second scenarios are far less likely due to their reliance on more than one failure to have occured. That said, I have replaced diodes and capacitors in my car. Test thoroughly for the first failure condition before we proceed to these next two. Hope the colored diagrams help, keep us in the loop.
COOL! I'm definitely posting in the right spot!
Thanks, professionalpyroman!! I'll digest all of this later. I'll check the sites you mention for downloads, too. Time for a shop manual!
I also believe it's time for me install some new plugs,...car ran (with warning light on and buzzer screaming!), but idle is poor. I guess that 30 years and 42,895 miles has finally taken a toll!
IT is the ONLY warning light I have,..ALL other functions and conditions are factory normal.
I've been a member for quite awhile, I'll keep this thread going to solution,...
All have a good rest of the weekend! Todd.
Just scanned through your post quickly,...actually the coolant sensing unit needs to see engine ground through the coolant level sensor for the light to go off and the buzzer to not sound after 9 - 16 seconds. The sensor sees engine ground through the coolant fluid path to the block.
The sensor is tested by removing it from the radiator, plugging the hole, and with engine running, the end of the sensor is grounded. A good sensor will turn off the light and buzzer,...neither my old one, or the brand new one, will,...
Direct grounding of the sensor wire does nothing to help,...
I see about 15 ohms through the newly installed sensor to ground.
I'm going to trace my sensor wire (through the enginebay) back towards the clock unit as far as I can. I'll let you know what I find,...
Todd.
Just hit up rotaryheads.com for their .pdf of the 1988 FSM. Section 15, part 2 was unavailable,...hopefully included in part 1. I'll check foxed.ca next. Thanks!
Good to see scanned auto literature! I provided a scanned copy of my '79 Fiat Spider Owner's Manual via mirafiori.com so that other's could use it,...just not available otherwise. Perhaps at Faxon Auto Literature,...
And I like foxed.com,...cool home page illustration! Downloaded another entire copy of the FSM. Fast downloads,...electrical section 15 is in one part.
Navy trained me in electronics way back, but with this information I should be able to figure this coolant level sensor problem out,...I'll update.
Gotta keep this "gorgeous" (but OLD) car up to speed!
Thank you very much for all your help,
Todd.
I replaced all electrolytic capacitors in my car (ecu included) this last year, and it was like a reverse country song. So many features came back. In the process, replaced some burnt out diodes and transistors as well. Some of the capacitors had rotted and were eating into the circuit boards, like in the car alarm computer. Fixing the ECU also helped me be able to tune the car as designated in the manual. If you have the ability and get bored, it might be a good upgrade.
Great bit of information here. I downloaded all those manuals some time ago and they are VERY useful to have saved . The parts listing is amazing to have also. This sort of stuff wont be around forever so download while you can and print it, copy it, save it while it lasts.
I agree 100%,...I have seven musclecars/trucks/sports cars 30+ years old and I have shop manuals for almost all of them. Invaluable information for maintaining the vehicle,...especially in a situation like this, where the Mazda dealership is rare/clueless, no one services the vehicle locally, and new/acceptable used parts are not to be found. Now I've got two full manuals for the Mazda. But, you know, both of them are wrong about the sensor testing,...and it's obvious, if read carefully.
Oh well, my Haynes has it correct,...it's an OLD manual,...
If it is a problem with the sensor unit, I'd be anxious to see what it consists of. I wasn't paying attention to it last time I was in the instrument cluster. I was mainly replacing capacitors and checking out the speedometer. It might be the bar of components on the board covered in coating. Be interesting to see what could be used as an upgrade/ replacement.
I finally got back to repair of this car, and got it into the garage. It did not take much time for me to find the "Low Coolant" sensor wire chewed in multiple places (and cut completely in two in a couple of spots) by mice. It's one of the few small wires that they can access from under the car,...they didn't leave me much wire, coming out of the loom, to work with!
A soldered and heatshrinked wire splice repaired the problem, and I sheathed the wire, to prevent further mischief,...
The car was sure ready for a drive! I've not been able to run the engine for very long, with the ear-splitting buzzer screaming continuously!
The car is back to 100% now! With an original 42,900 miles (exactly) on the OD, when parked today!
I have a brand new coolant level sensor in my car now, and my functioning original. I believe these are hard to obtain, but I also think it's an odd item, for a original car like mine.
If anyone needs one, I'll sell mine at cost + shipping,...I'm not greedy. PM me here.
I'm just glad to have my REX back on the road! WEEEEEE!!!!!!
Todd Compton.
12-18-18, 01:27 PM
