P0128 on 2007 Acura TSX

[artbuc]

This code appears if it takes too long for engine to reach normal operating temperature. Since I don't have any other hard or pending codes, is it safe to assume the thermostat is probably the problem? I'm thinking the ECT sensor is ok because I don't have any ECT specific codes. To avoid some extra work, I could change out the ECT sensor while I have the coolant drained. It only costs about $15 and should be a pretty easy job.

Should I stay with a Honda factory thermostat or would an aftermarket like Beck Arnley be ok? Thanks.

 

[Tegger]

It would be foolish to replace your OE thermostat with a factory one.

In any case, the problem is not the thermostat. It has to do with either the ECM misinterpreting Engine Coolant Temperature (ECT) sensor inputs, or with corrosion on the ECT contacts, or with a failing ECT sensor.

 

[beast3300]

This is usually fixed on GM's by replacing the thermostat.

 

[Roadkingnc]

Replace the tstat, the pcm is saying it takes too long for the coolant to warm up. An aftermarket one will work fine, Ill bet honda doesnt make thier own.

 

[Tegger]

Originally Posted By: Roadkingnc
An aftermarket one will work fine, Ill bet honda doesnt make thier own.

Do not use an aftermarket thermostat in a Honda.

 

[Tegger]

Originally Posted By: artbuc
This code appears if it takes too long for engine to reach normal operating temperature

How do you know the engine is taking "too long"? Does the transmission refuse to shift into overdrive?

 

[artbuc]

Originally Posted By: Tegger
It would be foolish to replace your OE thermostat with a factory one.


Foolish? Not sure what you mean here. I use the term "factory" and "OEM" interchangably. My question meant to ask can I go with an aftermarket thermostat or should I buy an OEM thermostat from Acura.

 

[artbuc]

Originally Posted By: Tegger
Originally Posted By: artbuc
This code appears if it takes too long for engine to reach normal operating temperature

How do you know the engine is taking "too long"? Does the transmission refuse to shift into overdrive?


I don't know that the engine is taking too long to warm up. I was just describing what Acura says about this code.

 

[yonyon]

Originally Posted By: Tegger
Originally Posted By: Roadkingnc
An aftermarket one will work fine, Ill bet honda doesnt make thier own.

Do not use an aftermarket thermostat in a Honda.


I'm with you on this one. Some aftermarket stats for Hondas will be missing a hole that's supposed to be there or come with a gasket that makes installation very difficult or will open 2 or three degrees two soon or too late.

 

[artbuc]

Originally Posted By: Tegger
In any case, the problem is not the thermostat. It has to do with either the ECM misinterpreting Engine Coolant Temperature (ECT) sensor inputs, or with corrosion on the ECT contacts, or with a failing ECT sensor.


Tegger, I think I found the confusing point. I have a downloaded Repair Manual which is supposed to cover 2003-2008 TSX but the pages are all designated 2004. In this edition, they call ECT2 a Radiator Fan Switch which grounds the fan relay and turns on the fan. I don't believe this sensor is fed to the PCM because there is no P2185 code listed.I believe later models (such as the 2007 in question) do have a P2185 DTC. In fact, I found a Honda Service Bulletin which describes how corroded contacts on ECT2 can cause P0128, P2185, etc. So I will do what you suggest and start with ECT2. Apparently corroded contacts are common since it is so close to the road.

 

[jim302]

If your scanner supports live data, it should show you the coolant temperature. With this information, combined with carefully feeling the hoses when it should be fully warmed up, it should be very easy to tell if the PCM is getting false data due to a bad sensor or some other issue (unlikely) or the thermostat is bad (likely).

 

[ComfyShorts]

Thermostat most likely. Tegger seems to be confused and probably shouldn't be giving other people advice.

Anytime you get a malfunction code instead of jumping the gun do some research, what does the PCM have to see wrong to trigger such code, in 5 seconds of research we find.

Quote:
P0128 OBD-II Trouble Code

Technical Description

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

What does that mean?

This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.

Symptoms

You will likely not notice any drivability problems other than the MIL illumination.

Causes

A code P0128 may mean that one or more of the following has happened:

Low engine coolant level
Leaking or stuck open thermostat
Faulty cooling fan (running too much)
Faulty coolant temperature (ECT) sensor
Faulty intake air temperature (IAT) sensor

 

[artbuc]

Comfy, I found a siimliar document in about 5 secs too- it is Acura specific and what I quoted in my first post. I also found a Honda S/B which talks about a chronic problem Hondas have with corroded pins on the ECT2 sensor which can, among other things, throw a P0128 code. So, I will check-out both ECT sensors but I believe the problem is likely a lazy thermostat.

 

[Tegger]

Hey, I forgot about this thread. I remembered only after checking the "My Stuff" link up top.

Maybe I was a bit hasty in dismissing a bad thermostat as being the cause of the P0128, but... Honda has had numerous known issues with various models since about 2001 that set a P0128 but have nothing to do with the thermostat. Plus Honda OE thermostats are of the best quality available, and very rarely go bad early.

The known issues are twofold:
1) ECM/PCM misinterprets sensor output. Usually requires reflash of PCM, or (rarely) replacement of PCM.
2) ECT sensor has loose or corroded connections.

Since American Honda closed the loophole (darn, heck, poopy!) in Techinfo that enabled me to conveniently gather TSBs and HSN issues free of charge anytime I felt like it, I have been unable to completely update my personal collection. This means I cannot confirm whether or not there exists a known problem with the OP's specific vehicle.

OP needs to visit his local Acura dealer, and have his VIN checked to see if there are any outstanding TSBs. More difficult will be to have the dealer read back issues of HSN for mentions there. That takes time, and they're monthly, not sorted by VIN or model.

If OP does not mind spending a whopping ten bucks for three days access, he can do his own checking. https://techinfo.honda.com
I haven't been on Techinfo in a while, but I don't think the subscription includes HSN.

If there are no outstanding TSBs or HSN mentions, and if there exist other symptoms, such as delayed upshifts into overdrive, then the thermostat is probably getting lazy. If that's the case, OP should stick to 100% Honda parts for everything from thermostat to coolant when he replaces the thermostat.