Car thinks that is overheating before starting up

[CookerBike]

For some context, I am rebuilding a 2016 ST that was modified by the original owner (who died) so I cannot get any references to the modifications he has done to the car. After plugging the battery in and putting the car in acc position, the temperature gauge rises even before starts up. I had already checked a temp sensor on the car and seems like it is in a functional condition.

Is there cylinder head temp sensor that is I don't know of, because I am about to give up and send it to a dealer

-thx!

 

[Handy Andy]

First, this is an ST that the previous owner died so that means no way to find out why this even happens...?

Ok, presuming the sensor is good, did you pull the connector and check for a voltage going to the sender?

To see this going on in the ACC position tells me the Original owner modified the vehicle and it's powering the PCM before you power up the car (Start it) - so yes, quirks like this are going to show up - including a set of mods that let the cars cooling system fans run a few moments longer to cool down the car and the turbo. When he sets up this mode after his drive.

This kind of leads me to think the owner ran this car hot a lot of times and needed some way of cooling down the system - so he forced the PCM to "stay up" and ACC position is where he set this up to cool down the car so he could even open the hood and not get burned after he let it run a few minutes.

This may also indicate that something in the PATS system is aware and is trying to shut down the car or put itself in a "limp mode" so someone trying to steal the car - knows it won't run very well for them.

 

[CookerBike]

First, this is an ST that the previous owner died so that means no way to find out why this even happens...?

Ok, presuming the sensor is good, did you pull the connector and check for a voltage going to the sender?

To see this going on in the ACC position tells me the Original owner modified the vehicle and it's powering the PCM before you power up the car (Start it) - so yes, quirks like this are going to show up - including a set of mods that let the cars cooling system fans run a few moments longer to cool down the car and the turbo. When he sets up this mode after his drive.

This kind of leads me to think the owner ran this car hot a lot of times and needed some way of cooling down the system - so he forced the PCM to "stay up" and ACC position is where he set this up to cool down the car so he could even open the hood and not get burned after he let it run a few minutes.

This may also indicate that something in the PATS system is aware and is trying to shut down the car or put itself in a "limp mode" so someone trying to steal the car - knows it won't run very well for them.

Thankyou for your quick reply. For the first question, the previous owner did some modifications to the engine. For what I can tell by looking, there is an aftermarket exhaust and cobb parts that is in the engine bay. I unfortunately cannot find any receipts nor records of modifications he has done to the car.

I did not check voltage, but I swapped the coolant temp sensor with a known good one but still arrived at the same results of the car thinking that it is overheating. I noticed through the DTCs that the cylinder head is sensing that it is "overheating." Is there a temp sensor for the cylinder head? I had looked through the repair manual and cannot find anything related to the cylinder head temp sensor

 

[Handy Andy]

There are others here that own ST's - I was hoping they'd chime in to help...

But to continue in the thread - the sensor, if you swapped with another and still get the same results - tells me there are even more questions - but to continue - the sender (the one on the cylinder head) is over by and just underneath the spark plug coil pack.

​

Is that the one you already checked?

There is a thread or two about this - here...
https://www.fiestastforum.com/threads/cylinder-head-temp-sensor-location.23475/post-397704

And it relates to an issue with the wiring and harness failure - which would fix this problem too, if this does apply.

That fix of the harness and it's returns - the results you get are similar - means that the drop across the sender is not getting back to the PCM to determine the actual temperature the engine is at. So that would put it in limp in mode and prevent the vehicle from being driven - even normally. So this may mean the voltage check needed - may also include a type of loopback test where you backprobe the sender to see if the sender can return a voltage back to the PCM thru a process of loading a known reference and altering it's output (Bridge network) as a means to fine tune the Air fuel charge just right per the MAIPT (Manifold Intake Air Pressure Temperature - amongst others) and the reading it gets from this sender.

Backprobe is to test using test leads of a style and type that lets you clamp onto the electrical wires to view the results on a DVM setup designed to test the signal or voltage results at the sensor itself - while it is in operation.

 

[CookerBike]

There are others here that own ST's - I was hoping they'd chime in to help...

But to continue in the thread - the sensor, if you swapped with another and still get the same results - tells me there are even more questions - but to continue - the sender (the one on the cylinder head) is over by and just underneath the spark plug coil pack.

View attachment 8750
View attachment 8752​

Is that the one you already checked?

There is a thread or two about this - here...
https://www.fiestastforum.com/threads/cylinder-head-temp-sensor-location.23475/post-397704

And it relates to an issue with the wiring and harness failure - which would fix this problem too, if this does apply.

That fix of the harness and it's returns - the results you get are similar - means that the drop across the sender is not getting back to the PCM to determine the actual temperature the engine is at. So that would put it in limp in mode and prevent the vehicle from being driven - even normally. So this may mean the voltage check needed - may also include a type of loopback test where you backprobe the sender to see if the sender can return a voltage back to the PCM thru a process of loading a known reference and altering it's output (Bridge network) as a means to fine tune the Air fuel charge just right per the MAIPT (Manifold Intake Air Pressure Temperature - amongst others) and the reading it gets from this sender.

Backprobe is to test using test leads of a style and type that lets you clamp onto the electrical wires to view the results on a DVM setup designed to test the signal or voltage results at the sensor itself - while it is in operation.

The sensor in the photo you provided is indeed the sensor I replaced earlier. I will test out the harness and will keep you updated!

Thankyou for your help, I genuinely appreciate it because this problem has been baffling me since I got this car. Have a happy holiday!

 

[CookerBike]

Update:

There are others here that own ST's - I was hoping they'd chime in to help...

But to continue in the thread - the sensor, if you swapped with another and still get the same results - tells me there are even more questions - but to continue - the sender (the one on the cylinder head) is over by and just underneath the spark plug coil pack.

View attachment 8750
View attachment 8752​

Is that the one you already checked?

There is a thread or two about this - here...
https://www.fiestastforum.com/threads/cylinder-head-temp-sensor-location.23475/post-397704

And it relates to an issue with the wiring and harness failure - which would fix this problem too, if this does apply.

That fix of the harness and it's returns - the results you get are similar - means that the drop across the sender is not getting back to the PCM to determine the actual temperature the engine is at. So that would put it in limp in mode and prevent the vehicle from being driven - even normally. So this may mean the voltage check needed - may also include a type of loopback test where you backprobe the sender to see if the sender can return a voltage back to the PCM thru a process of loading a known reference and altering it's output (Bridge network) as a means to fine tune the Air fuel charge just right per the MAIPT (Manifold Intake Air Pressure Temperature - amongst others) and the reading it gets from this sender.

Backprobe is to test using test leads of a style and type that lets you clamp onto the electrical wires to view the results on a DVM setup designed to test the signal or voltage results at the sensor itself - while it is in operation.

Update: From what I can tell, the coolant sensor electrical wires are bad and the sensor itself. I am going to order a new pigtail from rockauto and a new sensor and will keep you updated!
-thx!

 

[scotman]

Hopefully, your scan tool is enhanced so that you can see if it has had a different ecm map loaded into it, like a Cobb tune. I had a couple of overheating incidents with mine in traffic right after I picked it up in July 2016 that put me on a path to discovering that Ford had buffered the temperature sensor outputs even more heavily in the ST version than they did on the basic Fiesta. I had extensively auto crossed my 2011 fiesta and ended up adding a bigger cooling fan and a manual bypass switch along with a ducted and vented hood.
I ended up replacing the original radiator with a higher capacity one and replaced the original cooling fan relay as well in the ST.
I like the ST as a street driven car. But, i decided not to do any track days or autocross events with it. Mustang GT's are more capable of holding up to the stresses of track use.
I wouldn't be surprised if your Fiesta still has an aftermarket tune loaded into it.

 

[CookerBike]

Update: I ended up replacing the sensor and its connector, but it did not fix problem. Rather, some rigged solution ended up fixing the problem. Idk what this sensor is, but plugging the bare wires into this connector ended up fixing this problem. Maybe this sensor/connector is needed to complete the circuit? Idk, at this point. I have an urge to hardwire it and call it a day lol .

 

[CookerBike]

Hopefully, your scan tool is enhanced so that you can see if it has had a different ecm map loaded into it, like a Cobb tune. I had a couple of overheating incidents with mine in traffic right after I picked it up in July 2016 that put me on a path to discovering that Ford had buffered the temperature sensor outputs even more heavily in the ST version than they did on the basic Fiesta. I had extensively auto crossed my 2011 fiesta and ended up adding a bigger cooling fan and a manual bypass switch along with a ducted and vented hood.
I ended up replacing the original radiator with a higher capacity one and replaced the original cooling fan relay as well in the ST.
I like the ST as a street driven car. But, i decided not to do any track days or autocross events with it. Mustang GT's are more capable of holding up to the stresses of track use.
I wouldn't be surprised if your Fiesta still has an aftermarket tune loaded into it.

I think it does have an aftermarket tune, but i do not know how to verify it. I'll test it out the car tomorrow and verify if it is faster than a non tuned-car.

 

[Handy Andy]

Oh man, that is just wild!

So it needed what looks to be a different type of sending unit that gave more of a range and offered a full on (overheat detect) switch they could route to a relay that turns on the cooling fan without generating a code from it.

 

[scotman]

There isn't much difference between "normal" and " I'm about to burn down"in terms of what the temp gauge is saying about operating temperature at any given time except for a cold start.

 

[CookerBike]

What is even funnier about this is I am getting accurate temperature values with this sensor "plugged" into the connector I cold started the car and watch the temp values linearly grow on my live data graph. After looking around the engine bay for an extended period of time, I still cannot find the hole where this sensor is supposed to be plugged/screwed into.

 

[CookerBike]

The car sounds so good, considering I got it for 2500 bucks and low miles