PO 128 code need help
 

If this isn't the right place to post this, please let me know.

Recently my Honda Civic 2006 LX 1.8l check engine light turned on. Took it to the mechanic and told me the ECT sensor was defective. Cost me 100$ to figure only what the problem is, and was doubting the mechanic. Talked to a couple friends, everyone told me its the thermostat.

I bought a thermostat and a sensor when I went to the store. Tried the sensor, the check engine lamp turned back on after 3 engine start warm ups. So then I knew it wasn't the sensor. So I replaced the thermostat. Same thing happened again. After 3 warm ups the check engine light turn on again.

My prestone level is full. My radiator cooling fans only turn on when the engine is warm enough. I've tested my old thermostat in hot water and a thermometer and it is working perfectly.

After reading around, I've seen that the IAT sensor might be making this error to pop up. Where is this sensor exactly, and is it combined with the MAF as well? How can I test this unit before replacing it?

Any help would be very helpful, as I am getting confused by this. I've ruled out the most common problems and they aren't it.

The car has about 148k on it.

Thanks

A. LeBLanc

Re: PO 128 code need help
 

The testing for that code requires more than just replacing parts. Did you buy factory parts or aftermarket? Did you replace sensor 1 or sensor 2? In the actual testing information it says if you checked the sensors, thermostat and cooling system and found no problems you must update the software and possibly replace the ecu. You may need the honda hds to properly diagnose this.

Re: PO 128 code need help
 

Bought the ECT sensor from honda, sensor 1 only. Only figured out today that there is a second one on the bottom of the radiator, a real pain to get to and test.

Tested ohms on ECT 1 and got 3580 ohms at around 10-12 degrees celcius, and the same results on my IAT. Checked on the chart and the readings are right.

Seems like it may be sensor 2, but my hunch so far, it won't be it. Lets hope I'm wrong. Going to bleed completely tomorrow, remove and test sensor 2.

As far as the thermostat, that one is aftermarket. Replacing the original in tomorrow, while the system is empty, as I've tested it as well, and it opens exactly as intended, at 82celcius. Rather have the original in, considering how quick of a job it is to change.

Wish me luck on it being ECT 2.

Re: PO 128 code need help
 

The diag info actually wants you to monitor those sensors while running, and compare the readings between them at a certain temp. Not sure ohming them will be as accurate because the diag info states the values in degrees. Goog luck tho, hope you can beat it without going to the stealership.

Re: PO 128 code need help
 

2 possible issues, one is far more common than the other.

OP: Please read this

https://www.civicforums.com/forums/2...006-civic.html

Re: PO 128 code need help
 

Yes I've heard of this issue when I talked to the honda tech when I went to purchase the sensor. He called it a pig tail. While I was changing the sensor 1, I've checked the connections and the condition of the wires and they were just fine. Although I still used the "pig tail" in case it was something I couldn't see.

Since at sensor 1 it was fine, my bet is that sensor 2 is fine as well, but I will only know that tomorrow when I check on it.

Can I buy these connections at canadian tire? Or a similar store?

Thanks for your time and advice though!

A LeBlanc

Re: PO 128 code need help
 

Btw,

I am curious to know how a software update would help clear my problem. If for 6 years the car was working fine without having the code P0128 pop up, what would make it the computer "know" it needs an update? Does it change values for some reason?

I don't quite understand how that update would help, seeing as it was fine before...

An explanation of that would be nice, I'm confused by it's principles...

Thanks

A LeBlanc

Re: PO 128 code need help
 

Wrong assumption. You should find green corrosion and/or poor terminal fit, or a plain old bad sensor. MANY are intermittent, with an internally broken connection that surfaces when the pins get wiggled.
IF you had access to a GOOD scanner, this is easily diagnosed by watching the temperature value on the screen while wiggling the connections.

Sensor #2 is on the bottom of the radiator, hanging out in the weather and road grime.


It cannot "KNOW" it needs an update. It's not programmed to pop that code at 87,942.3 miles.

The engineers figure that crap out as a way to solve some issues, and supply us with really sketchy info about it. They give us an information bulletin saying "Hey, here's a possible fix for this problem".

Software fixes some AMAZING problems nowadays. Not just Hondas, but on almost all car lines that use reprogrammable control units that operate all sorts of different systems.

Some of our current recalls involve reprogramming.

No, a software update cannot help anything if there is a real problem with the sensors or wiring. Or if the thermostat was really bad. These would still cause codes to be set, they are real problems that the computer will still detect.



Microsoft Windows Update.
Nuff said?

Re: PO 128 code need help
 

Not looking to spend hours on theory, jusat tryin to help. What i posted for yu came from a honda factory service manual. If they say to check for software updates, then it is related and possible that it is part of the problem.
99-2000 era accords would develope starting problems after a hot soak in some cars. The fix as per honda was a different fuel pressure regulator and a new ecu.Things change in a motor as it wears and sometimes the parameters of the fuel calibration baseline has to be changed to match....software update.

Re: PO 128 code need help
 

Hey,

Just changed my thermostat this morning to the original, and checked sensor 2.

Sensor 2 is the culprit. One of the connections on it was all green of corrosion. I tested the ohms on it, and it was 120 000 ohms... Passed it through some CLR and am now getting the same reading as my other sensor and IAF. Currently around 2.5k to 2.9k. There is a large differential between them. I am still going to try it with just a simple cleaning. No harm done.

My only concern though, is the connection. The wire that connected to the sensor, I cant see if its corroded or not.

Any suggestions of what to do to prevent this corrosion further? Just replacing the sensor doesn't solve the problem at the source... Any ideas?

Thanks for your inputs!

A LeBlanc
Time will tell.

Re: PO 128 code need help
 

If in doubt you can put new terminal ends in the connector. Tou can take the connector apart, but its tricky to get the wires out of the housing. The ends should be available from honda but you will want to take yours along because they are made in different sizes. Basically you want to trim the wires back until you find good clean wire, add wire if needed and put the new ends on. Then reassemble the connector and plug it in. Or you can try to find a new pigtail ready to wire in. Cleaning the corrosion out of the wire is nearly impossible.
Making sure all of your connections are sealed will prevent corrosion. Heat shrink on wire splices and dielectric grease in the connector terminals.

Re: PO 128 code need help
 

Good answers there revr63ed7.

But Honda doesn't really give us pigtails. The aftermarket MIGHT have them though.


At work, instead of trying to match up terminals from a half dozen different boxed selections, then trying to find the correct crimping tool.......we hang on to ALL wiring harnesses that get replaced. This is a fantastic source of terminals and wire (and FAST too!). Quite often the proper connector body is there too. Now it's just a matter of connecting a few wires instead of literally building the damn thing new.
I know it doesn't help with your problem at the moment, but that's what I work with.




I figured it would be the culprit..Problem: The source of the problem is quite likely that the body of the sensor is leaking coolant past the terminal pins and into the connector terminals. The corrosion of the terminals and wires is collateral damage.
If you don't replace the sensor, this is likely to happen all over again.
If you choose to not replace it right now, then keep this in mind for when the same code pops up again later on.

Re: PO 128 code need help
 

Thats what we do too, its awesome to be able to snip off just the right plug when you need it. Sometimes if we don't have the exact connector i just pull terminals of the correct size from another and put them in the connector. Some of those connectors are a pain to get the terminals out of, like a puzzle.

Re: PO 128 code need help
 

Are you a tech?

Re: PO 128 code need help
 

We will see how it turns out.

At the moment the defective sensor is on the top where it is more accessible, so if it needs changing, I wont need to jack the car again. And the working sensor is on the bottom. I will wait for the check engine to pop again, and from there I will change the pig tail on the bottom and the defective sensor. Hoping something as simple as the CLR cleaning did the job!

I think the sensor I put on the bottom wont do the same as sensor 2 did, because it hasn't done it to plug 1. What do you guys think? Maybe the higher pressure on the bottom is what makes it corrode.

I still have to original plug from when I replaced the wire on sensor 1. I can use it to fit and find the proper plugs to replace the original on the bottom.

Thanks

A LeBlanc

Re: PO 128 code need help
 

Yes i am an ase master tech but not a certified honda tech as i believe you are. I do work at a private shop that specializes in honda, acura and subaru. Of course the newest stuff is not as common to me because the new cars are warranty. I'v been wrenching hondas for 15 yrs and its all i own (4 civics) except for my gixxer.

Re: PO 128 code need help
 

Hey,

Just to update, I've driven my car 4 times since I've "fixed" it and so far, the check engine light hasn't turned back on yet!

Thanks for the help.

A LeBlanc