pomona

Hi!

I have an 06 Civic LX.

I have the p0128 code so I know I need a new coolant temperature sensor.

I saw a vid on it, and saw that you can just unclip the blue thing, pop it off with a socket wrench, take the o ring off, and put in a new one.

I've seen some references of changing the coolant fluid, but I just had mine flushed and replaced last month.

Am I right in assuming that all I need to do is take out and replace? Also, should I buy a new o ring, too.

The temperature on the inside kept fluctuating between 3 and 6 bars on my ride today.

This is the part I'm looking at: http://www.autozone.com/engine-manag...2_214169_18589

Kim

ezone

Do you know the definition of the P0128 code?
Do you understand what it takes to cause the code?

Which coolant temperature sensor do you plan on replacing?

Have you checked anything on the actual car itself, such as radiator coolant level? How about the wiring for the temp sensors?

Do you have a scanner that can display live operating data?


Have you checked out any real service information on how to diagnose this code, or checked for service bulletins about this code?

ezone

The temp sensor in the radiator is ONE common problem area, wiring for the sensor is a possible issue.

There is a PCM software update for that code.

A faulty thermostat can cause the code, as well as low coolant level can cause it too.

The gauge on the dash mirrors what the PCM is seeing from the coolant temp sensor on the engine (not the one in the radiator), so I'd be checking for low coolant level first.

pomona

I will def look at my coolant levels and see a mechanic and probably Honda. They updated my software probably a couple years ago when I had an O2 sensor that needed replacing.

Why would my engine temp levels fluctuate like that then?

ezone

Figure out if the coolant level is low first.

How quickly was it changing?

pomona

I'm looking at replacing the one at the top of the engine. Ect 1. I know there's another one at the bottom of the radiator.

If I can't figure this out, it's going to the professionals. I want to be able to do more fixes on my own, but I also don't want to screw it up.

The code reading was at advanced auto parts. It said "P0128 coolant thermostat (coolant temperature below thermostat regulating temperature)"

kim

pomona

I will do that. The temp went up and down pretty quick. Like after several seconds or couple minutes it would go up or down a bar.

pomona

I can barely see any coolant in the main reservoir when I open the cap, and the reserve tank is at or below minimum. Hard to tell.

What makes the levels go down?

ezone

Locate the connector for the sensor in the radiator, disconnect it and check for loose terminals in the sensor, and for corrosion in the terminals and/or wetness in the sensor and harness connector.


The sensor in the radiator (ECT2) is used to operate the fans. I've seen many issues with this one, there's about 4 different codes that can be caused by this sensor and/or its wiring failing.

The sensor on the engine (ECT1) is used for fuel delivery calculations along with running the gauge on the dash. I've seen almost no problems with this sensor....so I suspect it may be telling the truth and you may have low coolant level in the radiator.
I mostly jumped on this post because there's more possibilities than just one temp sensor...and you can't DIY a software update.

On the plus side, if it did get a software update only two years ago it should have included the one for the P0128 code....but I'm not sure what would prompt a software update for an O2 sensor code.
Most people would have bought a thermostat and coolant.

The PCM uses both of the temp sensors to determine if the thermostat is actually regulating the engine temperature correctly......and if one sensor reading is changing wildly, it may still code for a thermostat just because it doesn't know what else it could be (the engineers didn't assign a fault code for a problem scenario such as this).

So if you figure out why the temp gauge swings wildly, that would probably solve the fault code.



And if the coolant was just changed last month....maybe that has something to do with it. Low? Leak?

ezone

Evaporation.
Someone didn't get all the air burped out at the previous service.

And the biggie....Leaks.


If the radiator (and engine, cooling system) is completely full, the level in the plastic reservoir will go up and down as the engine heats up and cools the liquid.
The system is designed to keep the radiator completely full under all conditions, as long as it's kept up correctly. It doesn't take much loss from the radiator to compromise cooling efficiency and cause overheating.



ONE bar isn't much sometimes.....

On a good day that could be the difference between driving along with wind keeping the radiator cooled (180-190*F), vs. sitting still and waiting for it to get hot enough the radiator fans have to run (212*F).

pomona

I think they were trying to diagnostic it to make sure it was correct. They cleared it and it re-appeared or something. I'm a little flakey on the details. But I do remember an update. I was trying to pass emissions.

I do find it odd that it's a problem after a flush.

Thanks for all your help, I will look at this again tomorrow when it's not night time. Add some coolant and go from there.

pomona

But it wasn't just one bar. That's nothing. It would go from 2 - 6 and from 6 - 2 in a matter of minutes.

Again, thanks. I will investigate further tomorrow.

Kim

pomona

Just to follow up on this:

ezone

Is '9 bars' roughly the middle of the gauge?
Middle of the gauge should be ok.
How many bars are showing on the gauge when the radiator fans turn on?

pomona

Yes 9 bars is def the middle range like it should be. (10 is middle). I was just thrown cause I don't remember it climbing up so quickly. It's a steady climb and takes under 5 minutes. I'm not sure about the radiator fan, I'd have to check.

ezone

P0128 was caused by the engine taking too long to reach operating temperature......and you probably got used to seeing it that way on the gauge.
Now that a good thermostat is installed it sounds like it's back to normal.

pomona

Thanks, that was what my gut was telling me.

Do you think it caused any damage to my car to have that needing to be fixed for over a month? Just curious.

ezone

No, it'll be fine.