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2006 Sentra, P0128 but heat is fine

Hello folks,

2006 Sentra with ~130K on the odometer.

Getting P0128 occasionally but the heat is fine. I will replace the thermostat in the spring. I am curious what else could be a problem and if it’s OK to run it until spring.

Thanks in advance

The thermostat for your car opens at 205 degrees.

So if there’s 140 degree air coming out the vent system it’s going to feel pretty damn good.

So if the engine doesn’t reach normal operating temperature, it could be wasting gas.

Don’t wait.

Change it now.

Tester

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The problem could lie in the related sensor or its wiring, or the problem could actually be the thermostat itself. Only a mechanic who can examine the car can determine which one is the source of the problem.

If the problem is the thermostat itself, then as a result of the coolant not getting hot enough, your oil is going to become diluted with water condensation and other contaminants much sooner than normally. Coolant that is not hot enough will definitely result in reduced gas mileage and can result in increased engine wear.

If I was in your situation, I would repair it sooner–rather than later–but if you insist on deferring this repair, I suggest that you start scheduling your oil changes much sooner than you usually do, in order to get the old oil out of there before it becomes too diluted/contaminated.

(Hint: If you are deferring the repair in order to save money, delaying the repair is likely to cost more in the long run.)

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I had that code, also had a temp guage, engine was runnin maybe 7 degrees below normal. The light goes on for a reason, getting an idea how much below temp it is running, and a mechanic may be able to advise you on the severity of your problem.

that code means the stat is partially stuck open and is taking too long to go into closed loop mode . You are wasting gas and if it is severe enough you could also risk clogging the catalytic converter which are big $$$ . If it is only coming on once in awhile then it is probably not severe yet and only partially stuck open .

Thank you, folks.

I was thinking to DIY. Its pretty simple but didn’t want to work in the cold. But if it is this serious, I will setup an appt with the mechanic.

fyi . . .

you can also get that code if the coolant level is low

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Tester

The thermostat may not be closing quite all the way so it takes longer for the engine to reach temp. This code requires the engine to reach operating temp within a time established by conditions. You may be reaching temp and so you could be good until spring.

In my experience the temp was 7 degrees low, the temp gauge was steady at 205 instead of 212, I would not see 7 degrees below normal temp a death knell. I do believe the thermostat was still regulating temp, just at the wrong degrees, not stuck open.

I rarely find “stuck” thermostats anymore, usually the poppet valve seal fails from old age. The internal leak causes a delay in warm up, the threshold for fault detection is usually about 160 F in 8 to 10 minutes while moving.

I have never tried this but can I get the engine temperature from OBD port? I have purchased Torque Pro app and OBD port adapter but haven’t used for anything other than getting the code.

You could be right. The light turned on when my wife was driving. She mentioned that the light turned on about 3 miles or so. It was 32F that night and the area where she drove out from has a speed limit of 30mph. So I think, it was definitely more than 10 minutes.

Yes. . . my professional scanner can see it

if you only have a cheapo code reader, the answer is no

Check your documentation. It may well have this capability. It appears to be able to display transmission temperature for some vehicles, so water temp is likely also available. I have a ScanGauge 2,and it has this as one of the standard gauges.

My car had bad thermostat due to it being stuck open.and I got 0128 after 10 min. And I also got 0118 which is opposite. Too cold and too hot. I replaced thermostat and codes both codes have not returned.
None can tell me why I got hot motor message with stuck open thermostat. Seems I am only gm car to ever have that issue.

At the very least, you should be able to get the freeze data at the time the fault was detected. This will tell you the coolant temp at the moment the fault was set, among other things. If the temp is almost up to norm, then you can wait until you have good weather to change the thermostat, unless you live in an area that has a smog check and it is coming up soon. Your ECT (engine coolant temp) may actually be up to norm on the freeze frame data, but it got their just a fraction of a second too late. I’ve had this happen to me.

I have BAFX OBD II Reader It is not as good as ScanGauge but does the job.

@keith
I am sorry, I didn’t understand exactly what you said, but I did a short drive yesterday just to check coolant temperature. The light didn’t come on and the highest the coolant temp. went was 167F. I could not find an option for the engine temperature. The overall behavior of temp gauge, warm air coming on, the way car ran, everything felt pretty alright.

I will be keeping OBD adapter until the light returns, just to find the temperature when the light comes on.
I am in a smog check state. Either way I will be replacing the thermostat on friday, if it arrives in time.

If you have a scan guage or app that reads LIVE data the ECT temperature should be in there . I have a Innova code reader with LIVE data and I recently had an issue on a Trailblazer where the temperature
guage would just go to zero . I thought it had been running cool . So I hook up the reader and low and behold it reads out the P0128 code with NO CEL . Found that interesting . So I cleared the code and low and behold the temp guage starts working again . So I drove it a few days and suddenly the guage goes to zero again , check p0128 is back . Took a drive with the reader hooked up and it never got above 175 , this model is supposed to be around 200-210 . Had shop replace the thermostat and it now sits right at the middle mark and no more temp guage going to zero . Dont know if GM has some weird programming or what for that code where it kills the temp guage . Heat is definetly a lot better too .

Do you have one or two thermostats? Some of the 2006 have two thermostats and they are not interchangeable.