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Falsely overheated

hey! i’m new to this site but i’m curious if anyone can help me or guide me in the right direction before i start ripping my car apart lol
a few weeks ago i was driving down the freeway and my protege overheated and shut off as it should and wouldn’t start again. tried to put water in it to cool it down but the thing is it never actually overheated. i took the radiator cap off and everything and it wasn’t hot either. it’s now been sitting since then and won’t start because the car still reads hot. i had a mechanic come out and look at it and tested the engine coolant temp sensor to find out that was giving off almost 3x the power it need. so i replaced that, also tried to replace the clip for it with new wires and no luck. the mechanic told me i need to trace back the wires to the harness and see where it’s burnt out at and go from there. i’m going to try and do that but was hoping someone else had more answers for me please!!

thank you!
 

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pcb

The Diagram Dude
:
2002 MP5
Firstly, check all your fuses under the hood and in the driver's side wheel well.

I remember helping a guy that had a problem with either his fuel gauge or his temperature gauge reading maximum.

I removed a fuse under the hood and my gauge went to maximum.


If that has been done then I think you have a bad connection/broken wire/open on your sensor ground wire.

It's the orange wire coming out of your ECU going to various sensors.

There is a bunch of sensors that use that ground and they may all be dead.


Normally, the car will run when it overheats until you warp the head so if I just spontaneously died you may have popped a fuse or the ground wire "broke".

It's not connected to engine or chassis ground and is isolated to go straight to the ECU.


If that is the case and if it were me, I would tap into the orange wire on pin #91 at the ECU and run a wire to the orange wire at the temperature sensor and all the other sensors can use it for there ground.

It depends on where the bad connection is and if all the other sensors can get past the bad spot and use it.
You may have to tap into a few sensors orange wire to get everything connected back up.


You could just try to trace that Orange wire and fix the bad spot but that can be a PITA.
I prefer to just bypass it all from both ends.











Maybe Mr Snurd can proofread my thoughts.

He seems to know hus stuff. Lol
 
okay so I have the ECU out now and i’ve never worked with wires before so can you possibly explain in a little more detail of what to do next?

sorry!
 

pcb

The Diagram Dude
:
2002 MP5
You need to test the continuity of the orange wire.

You'll need an ohmmeter set to ohms or continuity.

Disconnect the battery's negative cable first.

You need to probe the orange wire from the start at the ECU to the end of the wire at your sensor.


You'll need something like this with long probe wires to reach from the ECU to the sensor.





You need to touch the probe of the ohmmeter to the metal at the backside of the connector.









If the sensor wire connector is sealed, you can sharpen your probe to a needle point and poke it through the casing of the wire to contact the copper wire inside. (seal the hole up when you're done testing.)


If you and your mechanic are convinced that there is a bad wire, you can just simply tap into the orange wire a couple of inches back from the connector at the ECU and string a new wire to your temperature sensor.


You can use something like this to tap into the wire.







If you use these, put some grease in and on them to keep them from corroding


You're just piggybacking a wire so there shouldn't be any issues except the quality of the connection.

I would personally solder the tap wire in.


There is only one orange wire coming out of the ECU connector.

It is a solid orange wire with no stripe. It's located near the middle of the big connector.



 
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pcb

The Diagram Dude
:
2002 MP5
I tried to follow that orange wire though the various connectors and harnesses but didn't have much luck.

Replacing/doubling up that wire is what I would do.

Who cares where the break is, just replace the wire.
(keep in mind that you may have to add more orange wire splices...)

Good luck!!
 
is there a specific wire I need? or would any orange wire do fine from like autozone?

so far I got the ECU all out and i’m able to see where the wires are at plus it seems someone’s already cut that orange wire multiple times and reattached it so i’m thinking it just needs a fresh one and it’ll be fine.... hopefully at least.
 

pcb

The Diagram Dude
:
2002 MP5
is there a specific wire I need? or would any orange wire do fine from like autozone?
Color doesn't matter at all. It's just the gauge (thickness) that counts.



... it seems someone’s already cut that orange wire multiple times and reattached it...
You've found your problem.

Fix that connection.

Try to solder it.

You may not need any new wires.
 

pcb

The Diagram Dude
:
2002 MP5
Let me know if the orange wire is getting too short to get clean copper wire from for a proper splice. (like if it's covered in goo from electrical tape).

You can scavenge a wire "tab" from somewhere else in the connector to replace it.
They are removable.



 
Thanks.
I see that the same coolant sensor reports both to the ECM and to the cluster. In other Mazda cars they use a double duty sensor, half goes to the ECM the other to the cluster.

OP: Anytime you have a similar problem, check the engine's health with an OBDII reader. You're not specifically looking for codes but you want to see what the sensors are telling the ECM. There is a very accurate temperature reading setting in there. Personally I don't like Mazda temp gauges, they are no better than an idiot light since there is a big "dead band" between 180° and 225°. By the time you see the gauge start to move, it's usually too late. I run a ScanGauge 2 in one of the Miatas continuously monitoring the engine temp as well as the Intake air temp.

Before you start ripping wires it's best to make sure that you're on the right path to troubleshoot the problem.

Beg, borrow or ..... a OBDII reader, check the parameters and get back to us.
 
:
protege5
just my .02 here... I'm all about DIY and fixing things yourself. That's great. However auto electrical diag is a bit more involved than changing a belt or spark plugs. Of the many technicians/mechanics i've known or trained, (even dealership mechanics) about half, if not more, have the deer-in-headlights look when it comes to an electrical diag issue. electrical is one of those things that either you get it, or you don't. I'd recommend taking it to a reputable shop or a dealership where you can have someone work on it that knows what they're doing. Particularly with electrical, it's very easy to look for what would be (to me or someone else) a simple fix, and have that very, very quickly snowball into an absolute disaster and when it finally DOES go to a shop the cost of repair will be exponentially higher.
 
thank you Mr.Snurd for your help, i’ve actually had it scanned before and can’t quite remember what it said on it exactly but it was after i flushed the coolant system and replaced the thermostat. I know it read something about a manifold but not exactly sure what the specifics were.

as for going to a shop, the fact that i’ve already put in almost 4 hours just to figure out where the bad wire is would’ve cost me too much money. i’ve called multiple shops prior to this to just be told they can’t do it or they refuse to bc i’m looking at a huge price + since the car is older they don’t see the value in working on it. one shop told me just to diagnosis it could run me anywhere from $50-300 just depending on how long it takes.

that’s why i’m doing it myself, and if it doesn’t work then it doesn’t work and i’ll sell it to someone who wants a project car. (i also have a lot of guys who are doubting me on my capabilities so of course i have to prove them wrong lmao)
 

pcb

The Diagram Dude
:
2002 MP5
I also have a lot of guys who are doubting me on my capabilities so of course i have to prove them wrong lmao
There ya go!!!
Go for it!!!

I'm almost positive your issue is with that orange wire.
It was obviously a problem already.

If you can string a replacement wire from the ECU to somewhere in the Emissions harness, or one of the sensors using the orange wire, I'm pretty damn sure you can fix it.
 
you have NO idea how excited that makes me. i’m going to pick up some wires today and hopefully finish it.

thank you for all your help!! i’ll let you know what happens :)
 
:
protege5
All good :) I've worked on many of those "problem cars" that dealerships couldn't fix, and I've fixed it before it goes to lemon law arbitration. So I know how frustrating it can be chasing your tail. Good luck! With enough persistence you can get it, and sounds like you're good there. Just take your time, and carefulyl check things one at a time. If you start getting frustrated, it may be best to step back, and take a day off and go at it with a fresh mind. It's easy to get tunnel vision looking for something, and miss obvious things in front of you. We've all been there.
 

pcb

The Diagram Dude
:
2002 MP5
You don't need fat wire. It's just a low current signal wire and thick wire is harder to work with.

Get something about the same diameter as the orange wire.
 
:
protege5
Also, you can get these at hobby lobby, walmart, joanne's fabrics, or pretty much anywhere. These are excellent for backprobing into connectors without piercing or damaging the wire to check for signal. You can usually find them in the sewing section at walmart.

 
+1 on the "you either get it or you don't" when it comes to electrical problems.

When presented with such, I usually have it resolved 90% of the times just by spending a few minutes perusing the wiring diagram and following signals. The other 10% just from the symptoms.

Part of the problem for many people -auto "techs" included- is the way that the car's wiring diagrams are made, where they separate different systems by page with just connector or wire number to tie from page to page. Sometimes critical parts of a related system is several pages away.

Having it all in the same page makes it easier to follow and understand.

OP and pcb: Unless someone dorks with them [or get chewed by a critter], wies don't go "bad" on their own. At least that has been my experience in over 40 years of wrenching on cars and boats. :giggle:
 

pcb

The Diagram Dude
:
2002 MP5
Part of the problem for many people -auto "techs" included- is the way that the car's wiring diagrams are made, where they separate different systems by page with just connector or wire number to tie from page to page. Sometimes critical parts of a related system is several pages away.
I had the same problem trying to trace that orange wire from the ECU to the temperature sensor to try and find what connectors it goes through.
It would probably take me an hour to figure it out. Lol


OP and pcb: Unless someone dorks with them [or get chewed by a critter], wies don't go "bad" on their own. At least that has been my experience in over 40 years of wrenching on cars and boats. :giggle:
I live in the salty North East and I've seen bulb bases and sockets completely covered in white corrosion and no longer making contact and connector terminals covered in green corrosion or turning dark brown even black.
The connectors that have their wires sealed and a built-in grommet/seal within the connector fair much better.

Someone has already dorked with mihkayla's orange wire and spliced into it so that's definitely a good place to start.
 
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