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Discussion Starter #1
Greetings,
2012 Eco- two p0599 codes, CEL was on steady but turned itself off and not returned.
1. Using a voltmeter set on ohms/30 scale, I read .002 the across the 2 terminals of the 1.4 engine thermostat sensor/heater connector, that is a shorted circuit correct? Replace thermostat?

2. If sensor/heater is shorted and the ECM can't control the operation of thermostat, the thermostat may still open and close or get stuck, but is not very effectively controlling the coolant temperature? Thus the very wide swing of dic coolant temperature readings displayed. 195-247+ degrees. At 235 I turn on the cabin heat to help the reduce coolant temp.

Trying to be a DIY fixer. Thanks for the forum's vast experience helping us all.
 

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1. That's a dead short.
2. Not exactly sure what part your measuring, but I'd take your meter and go measure one at the parts store. Guessing your part is bad. Also check fusing for that circuit.
 

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Discussion Starter #3
Thanks for the reply.
I have a new acdelco thermostat arriving tonight. I'll measure the new one and compare with the old.
I am measuring across the 2 heater element pins on the tstat.
I saw this on South Main Auto Repair's youtube channel( it was a chevy sonic w 1.8 engine but I think similarly controlled) although he fully diagnosed the tstat control (p0599) issue starting with whether the ECM was trying to turn the heater element on or off (open or close the thermostat) which it was. Then determining that the tstat was indeed no good because of the shorted heater element.
 

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2014 LT program car, Pull Me Over Red
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Greetings,
2012 Eco- two p0599 codes, CEL was on steady but turned itself off and not returned.
1. Using a voltmeter set on ohms/30 scale, I read .002 the across the 2 terminals of the 1.4 engine thermostat sensor/heater connector, that is a shorted circuit correct? Replace thermostat?

2. If sensor/heater is shorted and the ECM can't control the operation of thermostat, the thermostat may still open and close or get stuck, but is not very effectively controlling the coolant temperature? Thus the very wide swing of dic coolant temperature readings displayed. 195-247+ degrees. At 235 I turn on the cabin heat to help the reduce coolant temp.

Trying to be a DIY fixer. Thanks for the forum's vast experience helping us all.
Not that it matters too much, but you mean resistance, not impedance. Impedance is an AC value and our cars are all DC.
 

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Discussion Starter #5
thanks, yes it does matter, and another example why this forum is truly priceless.
I can see how the parts fit together and assemble them, but even the most basic automotive diagnostic knowledge and experience is a long hill to climb...
 

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The PCM only partially controls the coolant temperature.
It's a conventional wax pellet operated thermostat, that typically starts to open at 217-221°F.
Under some conditions, such as prolonged heavy engine load, and WOT, the PCM will use the heater element embedded inside the wax pellet to make it open at a lower temperature, as low as 180-185°F.

Personally, I would recommend replacing it with the
Dorman 902-2080.
It regulates to 176-183°F, which helps to lower the stress on the rather delicate cooling system parts, and may reduce spark knock induced ign. timing retard, which may improve fuel economy some.
The thermostat mod is best used with the auxiliary cooling fan switch mod, and a lower pressure surge tank cap.
 

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Discussion Starter #7
Thanks, it is an interesting idea, I am not that bold of a diyr although it seems rediculous to stick with a stock design that obviously has serious issues... One thing is certain, my thermostat is bad, cold hose all the time last 2 days, stuck closed. Putting a new one in tonight. I am very adapt at using the cabin heater to keep engine temp under control. Removed the cabin air filter and got some serious air flow going over the heater core.
Maybe I'll write a tutorial on that...
Thanks for the input
 

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Discussion Starter #8
I got the new acdelco tstat, radiator sensor, outlet sensor, and new dorman tank installed. I followed the alldata coolant bleed instructions and all seems good. On my hway/city test drive I could'nt get the coolant temp above 230. We'll see if cel turns off after couple cycles.
 

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Discussion Starter #9
P0599 Resolved.
Symptom was tendency to run hot, up to 250f. I used the cabin heater to keep coolant below 240f until parts arrived.
Diagnosed issue by checking the radiator to thermostat hose, it stayed cold even after lengrhy drives. Tstat stuck closed.
After work was completed(previous post), coolant temp centers at 223f on highway drives.
CEL turned itself off after several drive cycles.
As for the title of this thread, I had no success at electrical measurement to diagnose the issue. A qualified mechanic with proper skills would have solved this problem faster but I saved lots of money, diy.
 

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Thanks, it is an interesting idea, I am not that bold of a diyr although it seems rediculous to stick with a stock design that obviously has serious issues... One thing is certain, my thermostat is bad, cold hose all the time last 2 days, stuck closed. Putting a new one in tonight. I am very adapt at using the cabin heater to keep engine temp under control. Removed the cabin air filter and got some serious air flow going over the heater core.
Maybe I'll write a tutorial on that...
Thanks for the input
I had a discussion with @Robby about why the Gen I Cruze runs such a high temp and this is what he had to say:

...[W]hy the need for the higher opening temperature for the factory thermostat[?]

There are several reasons with the primary being fuel economy and emission control. Keep in mind, a correct mix of coolant to water ratio raises the boil point to 223 degrees f at atmospheric pressure. The boiling point of a 50/50 mix of coolant/water under pressure, (in this case, 20psi.....the coolant cap on the Cruze) is 275 degrees f.

So, the factory setup of coolant/water and 20psi cap allows for, approximately, a 50 degree cushion before boilover. The high pressure reduces the possibility of steam cavitation in the cylinder head water passages surrounding the exhaust valves and tends to keep temperature the same throughout the cooling system.

[Additionally] operating temperatures above 200 degrees reduces piston ring wear....this equates to a friction reduction and a mileage gain.
The higher temperatures contribute to complete combustion, lower emissions, lighter load on emission controls (specifically the catalyst, since it isn't burning as much unburned fuel from incomplete combustion). This allows the fuel mixture to be leaned further based on information from the coolant temperature sensor.

Oh, yeah......the heater works better too, heh heh.

With the above in mind, a thermostat that is open at lower temperatures negates all the engineering work that I stated above......wear, mileage, emissions all will be negatively affected......heh, along with lousy heat. Keep in mind that heat complaints are regional.....we live in an area where the cold can overwhelm this cars heating system and that is because this little engine is almost too efficient. Efficient engines do not lose as much heat into the cooling system.....they use their energy to turn a crankshaft.

Naturally, the operators that live in temperate climates don't notice poor heater performance, so, when reading posts about cooling systems, notice where the writer lives in their signature. Usually they live South of the Mason Dixon line.
 

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One issue is very apparent with these engines and it's heat soak. When my car runs cruising the coolant temp is around 225 and my oil temp is 240. Turn the car off and those temps rise and with that heat and pressure on the cooling system and all the plastic in the cooling system. One little leak you don't notice and the pressure drops and you'll start warping the aluminum without an overheat. Hot spots and steam. This was done for best emissions, not what's best for the engine you rely on or the turbo.
 

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Look at any other vehicle on the market. Why is the 2nd gen Cruze not running at the same thermostat operating temp? That waa would mean it gets less fuel economy and more wear???? Come on now... the gen 1 is pushing the envelope and walking on a tight rope... look at how many cooling problems the vehicle has along with how many head gasket and warped heads. Yea the coolant isn't boiling but i dont want the Aluminum head reaching such high temps. Hey heat soak up to 250 but the coolant isn't boiling so all that metal is fine.. wrong...
 

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I believe there are more overheating issue post on this forum as there is with the PCV system. Especially post about heat soak and using different plugs to try and fix the hesitation while running the AC. Regapping plugs and having to buy a coolant pressure test and constantly inspect your engine with a magnifying glass cause of how hot the car runs is turning out to be a pain the in arse.
 

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I'm just saying, if it was a great operating temp... you would see more manufacturers doing the same and GM wouldn't have reverted back to a lower thermostat on the 2nd generation cruze.
 

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My all aluminum block 2.3 ranger runs in the 250's pretty regularly during the summer... 293k miles...
 

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Throw some water wetter in there...
Dexcool is not my preferred coolant... I recommend flushes at the service interval which most people don't do...most people also don't let their cars gently warm up and cool down... just key on hammer down...
Cars like everything else are getting more advanced, old cars remove thermostat and run wide opening the summer and reinstall in the fall...
 
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