Honda Civic Forum - Code p0128

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- 7th Generation Civic 2001 - 2005 (https://www.civicforums.com/forums/182-7th-generation-civic-2001-2005)

- - Code p0128 (https://www.civicforums.com/forums/182-7th-generation-civic-2001-2005/349498-code-p0128.html)

Hi guys I'm new here I have been doing some research as of lately to try and figure out what is wrong with my 02 civic lx. I guess you need the car specs first. All stock except the k&n drop in air filter I have. 144000 miles no leaks no drips just changed to full synthetic abut 2-3 weeks ago.

About 3-4 days ago coming home from work I turned on the car let it warm up for about 5-7 minutes got in started to drive away and than the engine light popped up. Once I got home I plugged in my obII reader and it gave me the code of p0128. On the way home the car was running fine no overheating nothing out of the ordinary. S once I got home I cleared the code and than 2 days later it popped again. This time I got a new thermostat from autozone and some coolant that I miked 50/50 myself. Drained the radiator removed the old thermostat installed the new one and I thought all was fine till this morning. I started the car it warmed up for about1-2 minutes and than I took off I was running late about a half a mile it popped and again same code I took my reader with me just in case. Leared it on the road.

When I got home I did Some reaserch and I did not turn the heat to on full. So when I got home I turned on the heater waited for the fan to kick on twice filled it up and capped the radiator. I siphoned the resivoir and put in clean fluid.

The coolant gage reads 1-2 lines below half way. Idles fine no smoke runs great.

This is also what i did...

The electric sensor on top of the thermostat when the engine was warm I unplugged it andyup the engine light came on no surprise, than I loosened the sensor to try to drain any air out of the system tightened plugged in the sensor cleared the code.

I Also drained about 2 cups from the radiator a added straight water since water is a better conductor of heat then the glycol.

What I think I have left...

I could install 2 new sensors but I read they don't have a high fail rate..?

Try a new thermostat ..?

I also found out that there is Ecu update I called 2 honda dealers the local one said there was a update and would cost 105.00 to do but could not tell me if my car already had it done. The second dealer is where the previous bought the car I called them gave them the vin and couldn't find anything abut an update. I even gave her the bulletin number no luck...?

That's my issue I know I'm new here but I would really appreciate the help !!

Tony

Yes, there is a software update for the P0128, that should be done first. (Bulletin 03-002)
Check different dealers for a price, we are only getting about half of that number for a single software upload into one control unit.

There is no way to tell if the car already has the newer software, we MUST connect the little electronic gizmo to the car to find out.

Use a factory thermostat with a new seal.
Don't bother with cheapos, they have a high fail rate and tend to open at a lower temp than what it should.

An inaccurate temp sensor can cause it too.

But...
The code set because the computer is seeing a coolant temperature that is lower than it thinks it should.
The software update (reflash) changes what the computer thinks it should see.

CopyPaste from the Honda site, Service News Oct. 03:

The problem may not be the coolant
thermostat, but a deficiency in the ECM/PCM
software. Under certain driving conditions after
a cold start, the ECM/PCM can miscalculate how
fast the engine coolant temperature rises and set
DTC P0128 or P1486.
If the heater and temperature gauge work OK,
don’t replace the thermostat for this DTC; it
doesn’t give a lasting repair.

HTH

Ok I will call other Honda dealers in my area and check on the update. If the dealership is honest once hey plugin the gizmo and it had the update I hope they are honest. Not to fond of stealer ships.

Thanks for the info

Last question could I do the update? My obdII reader has a mini USB port is there a program I could use. Also is this update only performed at a dealership?

Tony

AFAIK, only dealers and extremely well-equipped indy shops that paid the big loot for the subscriptions to factory data and factory tooling.

No DIY for you. Sorry.

Ok thanks. I'll find a good dealer and get it done

Tony

You would not happen to live in southern California would you..?

I'm just a hop, skip, and a jump away......like a little over 2000 miles.

yeah thats a little far for me !! I found a local dealer, Honda Dealer that will take care of it in the morning for 49.00 and 2 recalls.

Thanks again for the help !

Tony

That price sounds quite reasonable IMHO.

Remember, the flash will only fix it if it is a falsely set code.
If the code is real, then it is a real problem-- the flash can't fix that.

I have done everything I can think of to try and fix it. The light comes on about every day and a half. It runs great the temp does not go past the half way mark its actually a little under. Im also going to pick up a honda thermostat and 2 gals of coolant just in case it does do it again.

If the light does come on again I will replace the ECT i believe there is only 1... I would need to double check..

The flash to the ecu will do what exactly set different parameters ?

Dont know but thats my plan hope it works.. let me know if there is anything else I should do !! Thanks again

Tony

I have done everything I can think of to try and fix it. The light comes on about every day and a half. It runs great the temp does not go past the half way mark its actually a little under.

Would be nice to see what the computer actually is reading the temps as (real values), AND be able to verify the temps read are actually accurate.

Im also going to pick up a honda thermostat and 2 gals of coolant just in case it does do it again.

If the coolant isn't very old, I'd just slap it in without draining the coolant.
Let it dribble whatever out and top it off when done.
Maybe a quart or two?

If the light does come on again I will replace the ECT i believe there is only 1... I would need to double check..

See, I can't just guess and throw parts.
I test so I can make the right call the first time. If there is only one problem, then I take care of just that.
If the sensor is accurate, then there is no need to replace it.

Anyway....
The CTS for the PCM is what you would want.
Wires: green/yellow and red/white

The flash to the ecu will do what exactly set different parameters ? Yes.

Dont know but thats my plan hope it works.. let me know if there is anything else I should do !! Thanks again

You have it pretty well covered. YW
HTH

Welt did it again after the computer update. Twice today still runs great no problems. Going to replace the sensor if that font work I'll replace the thermostat. And if that don't fix it I probably have some sort of computer problem or wiring.

Darn it I thought I had it figured out.

Tony

Also getting code p0118..

Quote:

Originally Posted by Last2die (Post 4606694)

Quote:

Originally Posted by ezone (Post 4606186)

Remember, the flash will only fix it if it is a falsely set code.
If the code is real, then it is a real problem-- the flash can't fix that.

Quote:

Originally Posted by Last2die (Post 4606694)

Also getting code p0118..

P0118: ECT Sensor Circuit High Voltage
Is it bad? Is it unplugged? Does it repeatedly set this code? If this was in the middle of an actual failure (false temp readings), it could be a possible cause of the P0128.

You could have the wiring terminals inside the connector too loose to make good contact on the sensors terminals.

I'm just guessing here.

Would be nice to SEE the PCM data live, I hate guessing.

It is quite possible that this had an easy answer in the beginning, and now some perfectly good parts got replaced with cheapo junk--- and you have to get through all of those before it will be right again.
I know you said you have a ChinaZone stat, is there anything else you did that didn't use factory parts?

Just the thermostat. I replaced the sensor and I also removed the thermostat and ensured the hole that's in it is facing up don't know if that makes a difference. Really the only thing left I can do is replace with oem thermostat. If it still happens maybe a computer problem?

The code p0118 just started today. Hopefully the new sensor will fix that..

Fix the sensor first, since it is an obvious problem.

Next would be the factory thermostat.

The hole in the stat goes UP, it is an air bleed.
Should be a jiggle pin on a factory stat, make sure the rubber gasket doesn't get caught on the pin.

If you could get PCM data, you wouldn't have to guess at a lot of this. (Well, *I* wouldn't have to...)
The P0128 is operating temperature too low, or took too long to reach operating temperature.
A faulty temp sensor sure could do this, and so can a thermostat.
Being able to read PCM data takes a lot of guesswork out of the picture.

I'm pretty sure it won't be a PCM.

HTH

An update after ensuring the thermostat air hole was straight up which it was not and replacing the sensor all seems to be ok. This is my second day driving it and no light yet so hopefully that took care of it. Thanks for the help !!!

Tony

Now it's time to check out the compliance bushings...