Coolant temperature sensor

As far as money, the things I have replaced are cheaper than one trip to the shop. The dealer overcharges, and just because a part has Mazda's name on it, doesn't mean its better than what you get at a parts store. It might take longer for me to figure out what the problem is, but i prefer to figure out and know I'm not being ripped off by the dealer.

+1. Avoid dealer at all costs. They always screw each customer, always. Besides low probability of diagnosing the issue they want to sell unneeded services for 500% markup. Always.

Their service centers are Mazda certified cash cows.
 
I'm not gonna go out and buy an extended warranty because I feel the CX-5 is going to be reliable in the long haul but basic powertrain warranty does seem somewhat weak. I can understand things like an AC exclusion but all sensors that ensure the engine is running properly should be included. Heck... it should be under the Federal Emission warranty if nothing else since the engine's knowledge of temps could affect emissions.

EDIT: I guess not on Federal

Emission Control Parts
1. Exhaust Gas Conversion Systems: oxygen sensor, thermal reactor, catalytic converter,
dual-walled exhaust pipe
2. Exhaust Gas Recirculation System: EGR valve, thermal vacuum switch, EGR solenoid,
EGR spacer plate, EGR backpressure transducer, sensor and switches use to control EGR
flow
3. Evaporative Emission Control System: purge valve, fuel filler cap, purge solenoid, vapor
storage canister and filter
4. Positive Crankcase Ventilation (PCV) System: PCV valve, PCV solenoid
5. Air Injection System: Air pump, diverter, bypass, or gulp valve, reed valve, anti-backfire
or deceleration valve
6. Early Fuel Evaporative (EFE) System: EFE valve, thermal vacuum switch, heat riser
valve
7. Fuel Metering System: electronic control module (unit) or EFI air flow meter, computer
command module or mixture control unit, deceleration controls, electronic choke, fuel
injectors, fuel injection units and fuel altitude compensator sensor, bars or rails for EFI
or TBI systems, mixture settings on sealed fuel mixture control solenoid, diaphragm or
other systems, fuel metering components that achieve closed/other feedback control sen
sors/loop operation switches and valves
8. Air Induction System: thermostatically controlled air cleaner, air box
9. Ignition Systems: electronic spark advance timing advance/retard systems, high energy
electronic ignition
10.Miscellaneous Parts: hoses, gaskets, brackets, clamps and other accessories used in the
above systems
Emission Related Parts
These are examples of other parts of your vehicle which have a primary purpose other than
emissions control but which nevertheless have significant effects on your vehicle’s emissions. If
any of these parts fail to function or function improperly, your vehicle’s emissions may exceed
federal standards.


Therefore, when any of the parts of the following systems are defective in materials or workmanship and have failed in a way that would be likely to cause your vehicle’s
emissions to exceed federal standards, they should be repaired or replaced under the emissions
warranty:
1. Fuel Injection System: fuel distributor
2. Air Induction System: turbocharger, intake manifold
3. Exhaust System: exhaust manifold
4. Ignition System: distributor, spark plugs, ignition wires and coil
5. Miscellaneous Parts: hoses, gaskets, brackets, clamps, and other accessories used in the
above systems.
Getting the Mazda extended warranty probably wouldn't have even helped here, it appears it's just an extension of the original power train warranty.
 
My bet is the thermostat. Run the car for 20 minutes and feel the hoses. Top radiator hose should be very warm to hot. Both heater hoses should be warm. If one is cold you have a blocked heater core, not likely on such a new car. Feel the top radiator hose while the engine is warming up. There should be a point were it gets hot fast, that is when the thermostat opens. If it stays cool to warm and never really gets hot the thermostat is stuck open. I am sure that would throw a code. I agree, only buy oem thermostats.
 
I've already replaced the thermostat. After checking everything out and not noticing any issues I took it to the dealer. Of course they charge $90 just to check it (scam artists). They tell me its an issue with the computer needing reprogrammed and that it was going to be done free due to a "bulletin" but I still had to pay the $90 diagnostic fee. A bulletin sounds pretty freakin' similar to a recall except they only fix it if you have the issue and bring it in, instead of them announcing it nationally. But i just paid it to be done with this once and for all. They "fixed" it. and two days later the light came back on! I dropped it off at the dealer this morning, so they can actually fix it, but I guess we'll see what happens. I'm hoping its a ECU or OBD computer issue because by law those have to be warrantied up to 80,000 miles. FYI if you take this issue to a regular shop instead of a dealer you can get screwed because the shop doesn't have to tell you its under the Emissions warranty since they don't own the car company. Here's the link to the EPA info on emissions warranty: http://www3.epa.gov/obd/pubs/420f09048.pdf so you can check yourself. Emission control and emission related parts are covered for the first 2 years or 24,000 miles of vehicle use (whichever first occurs). Specified major emission control components are covered for the first 8 years or 80,000 miles of vehicle use (whichever first occurs). I really think its the ECU because my average miles per gallon is gradually decreasing even though my daily routine or driving isn't changing.
 
Update: Mazda dealership just called me. They said they tested everything and its all checking out fine. They called the head mechanics at Mazda to explain everything and see what they said. They said it might be a faulty Coolant temperature sensor next to the firewall and that would be $101 with parts and labor. I told them I just replaced both sensors. All they suggested was trying to replace it with another one. Even though they tested it and it gives off the correct voltage. When the company that makes the car cant figure out whats wrong there's an issue!
 
Update: Mazda dealership just called me. They said they tested everything and its all checking out fine. They called the head mechanics at Mazda to explain everything and see what they said. They said it might be a faulty Coolant temperature sensor next to the firewall and that would be $101 with parts and labor. I told them I just replaced both sensors. All they suggested was trying to replace it with another one. Even though they tested it and it gives off the correct voltage. When the company that makes the car cant figure out whats wrong there's an issue!

Sounds like Mazda sucks in your opinion. Why don't you just spend the money, fix it, and get rid of it? Even if they fix it, you'll be pissed they charged you.
 
I enjoyed reading this thread, having spent most of my life in technical maintenance, the OP in my opinion hasn't approached the problem in a logical manner.

Not trying to be clever here but just replacing sensors with out testing first is chancy, before replacing a sensor that can be tested test it first.
Even the thermostat if its anything like those from 30 years ago can be tested in water to check its action.

I admire the OP attempts at rectifying the fault him self, but not his illogical way of doing it. Does sound at this stage a faulty connection, tracing that out can be very involved unless the wiring route can be easily followed, or you know where the cable terminates.

Intermittent faults can take days to sort, and sometimes more than one fault can be present, up to three problems I've had in the past in my work experience, more than once.

On some old cars removing coolant could result in a cold heater due to an airlock.
I agree the reliability of Mazda isn't very convincing.
 
There’s a specific troubleshooting flow chart for this error in the shop manual, starts with checking connectors at the sensor AND the PCM. I would go to the PCM and pull the connector and check it, check to see that none of the pins moved back and maybe spray some contact cleaner at both ends. First rule in troubleshooting, always go for the simple stuff first.
 
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I enjoyed reading this thread, having spent most of my life in technical maintenance, the OP in my opinion hasn't approached the problem in a logical manner.

Not trying to be clever here but just replacing sensors with out testing first is chancy, before replacing a sensor that can be tested test it first.
Even the thermostat if its anything like those from 30 years ago can be tested in water to check its action.

I admire the OP attempts at rectifying the fault him self, but not his illogical way of doing it. Does sound at this stage a faulty connection, tracing that out can be very involved unless the wiring route can be easily followed, or you know where the cable terminates.

Intermittent faults can take days to sort, and sometimes more than one fault can be present, up to three problems I've had in the past in my work experience, more than once.

On some old cars removing coolant could result in a cold heater due to an airlock.
I agree the reliability of Mazda isn't very convincing.

(detect)
Well said!

At this point, you would almost want to reinstall all of the parts you removed, Or at least test the old temp sensors and thermostat to see if any of them were indeed faulty.

However from the OP it sounds like it might end up being a damaged wire or dirty connector caused by road debris, under hood gnawing animal, corrosion, stereo modification, etc? Testing the impedance of the wires between temp sensor connector and ECU connector might show you a damaged wire?

(rei)
 
Update: Mazda dealership just called me. They said they tested everything and its all checking out fine. They called the head mechanics at Mazda to explain everything and see what they said. They said it might be a faulty Coolant temperature sensor next to the firewall and that would be $101 with parts and labor. I told them I just replaced both sensors. All they suggested was trying to replace it with another one. Even though they tested it and it gives off the correct voltage. When the company that makes the car cant figure out whats wrong there's an issue!

Check out this TSB.
http://oemdtc.com/29250/dtc-p011a-andor-overheating-condition-2013-2016-mazda-cx-5


Originally posted here by Kedis82ZE8:
http://www.mazdas247.com/forum/show...-2014-Mazda6&p=6415124&viewfull=1#post6415124
 
I appreciate the advice on here that's actually helpful. It seems that some ignored the part where I had it checked out by the dealership in order to get it over with. They told me everything they did. So far they reprogrammed, flushed the heater core to make sure it wasn't blocked, tested the ECT sensors, checked the wiring harness for issues, and made sure the engine and cooling system were good with temperatures. As for Spock boy suggesting I'm not going through the steps logically, I checked the easiest stuff first, coolant level, hoses, connections, etc. After that I went to the shop manual (created by Mazda) and took their steps to diagnose the issue according to the code that appears on the scanner. Then I took it to the shop for them to figure out and they couldn't even do it. Hows that for logic?
 
Update: After maxda suggested I recplace the ECT sensor again, I did just in case I got a defective one. The check engine light came right back on the next day. I know what the symptoms are pointing to (heater core blockage, or bad thermostat) I took out the thermostat to do the boiling water test. The engine was cold and the thermostat was closed when I took it out. It worked exactly like it should when I put it in boiling water. I put it back in, put the coolant back in, and burped the cooling system. Light came right back on. You can probably imagine how badly I want to take a sledgehammer to the car right now. I gave up and took it back to the dealership. Told them everything I did and what it was doing (No heat/Same trouble code/new sensors/working thermostat) They checked the heater core for blockage again and said water goes through with no problem. So they told me they would have to replace the Thermostat. When I told them I already did that all they could say was it must be stuck open. FYI I paid them to do that they would charge me over $220! The mazda brand thermostat cost $54 from them and they had to order it. I found another mazda dealership that only charged me $20. So I got that one. I am going to go through this annoying process again and hope that for some reason the thermostat currently in place opens too early. So far I had to pay 2 separate $90 diagnostic fees for the dealership to check it and tell me what they think it is instead of knowing and actually fixing it. If its not fixed this time i'm going to lose it on the dealership. On the upside, I am now very familiar with how to take how the thermostat while making the least mess possible. Nothing against mazda, just the one I have. Maybe I'll become a mazda mechanic so I can charge $90 an hour on "fixing" things just to have the customer return a day or so later.
 
What are you using to clear the codes between each repair attempt?

Have you tested the ECT Wire harness for damage between the ECT sensor and computer connection?
With a multimeter, I would test ohms from ECT sensor connector to the computer connector.
 
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Originally I used an OBII scanner to clear it. I'm assuming the dealership used theirs to do it as well. Also, the repair manual that the shop uses says to removed the negative battery terminal when replacing the ECT sensors, and the whole battery to replace the thermostat. In both cases I hooked up my scanner after the repair to read the live data in which shows a major temperature difference between the two sensors (at least 30 degrees F). The mechanic at the dealership said it points to an open thermostat. I'm not convinced. If it comes back on after this fix, I'm going to tell them it has to be a bad wire or an ECU issue. They already checked the wires though. And I know they probably don't want it to be an ECU issue because that has to have a warranty up to 80,000 miles by law according to the EPA.
 
At this point, I would pull out the ECU, and as mazdadude said, look at the connections and make sure they look clean.

Looking at the service manual it looks like pins:
2F and 1AM (GND) go to ECT#2
1AK and 2AJ (GND) go to ECT #1

With the PCM pulled out I would measure the resistance across each sensor with a multimeter. The resistance measured should correspond to the temperature at each sensor.
 
Yeah, the mechanic at the dealership tested that already. He even gave me the diagram of the ECU pins highlighted with what he tested. But Just to make sure I will check that out myself also.
 
Yeah, the mechanic at the dealership tested that already. He even gave me the diagram of the ECU pins highlighted with what he tested. But Just to make sure I will check that out myself also.

Yes, I can understand how frustrating this must be.

So both ECT's have been replaced, thermostat replaced, wiring checked, heater core checked...

Running out of ideas...
Has the ECU been reflashed with latest update?
Is it possible to accidentally swap ECT1 with ECT2?
Is it possible to install the thermostat backwards?
Prior to the very first check engine light over a month ago, had you had any recent services, changes, upgrades, stereo, LED bulbs, headlights, jump start, alarm, tow hitch, etc...?
 
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Both ECT's are the same exact part number. I am about to replace the thermostat just to make sure the current one isn't defective. The dealership checked the wiring and heater core. The first time I took it to the dealership they reprogrammed the computer so that should have been the latest update. Hopefully their systems don't start needing updates like iphones. The thermostat placement is pretty straight forward with the shop manual diagram. There's a rubber gasket around the rim of the thermostat that can only be inserted one way. The shop manual says to make sure the jiggle pin is aligned with the notch, which I made sure it is the right way. Prior to the first time the check engine light came on, there were no recent changes. Last service was done in July which was just new tires at a shop that I have been going to for years and they are really good guys. I took my car to them about this issue and they suspected the ECU and said the dealer has to do it becasue Mazda hasn't released it for none dealerships yet.
 
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