Can air in cooling system cause P0128?

[Natasha]

While doing a coolant replacement, can I get air into the cooling system and cause the ECU to throw P0128?

If so how to check for it? (I don’t want to go on a dead end trying to get air out of the system where the problem was with the thermostat all along)

What are the steps to find out if it’s a thermostat issue or sensor issue or “air in the system” issue?

While I can test each of thermostat and sensor individually, I am asking to see if there is a smarter way to figure this out

If this is vehicle specific, please let me know (in which case it’s a 2000 Honda Civic)

Topic

[Dave Tidman]

Air id the cooling system usually leads to overheating, the P0128 is an under temp. Usually this code is the CTS or thermostat. I would check the CTS first using a multimeter on the signal wire. The table on this page (http://www.autozone.com/repairinfo/repairguide/repairGuideContent.jsp?pageId=0900c15280076b7b) is a good guide. If that is OK, it’s likely the thermostat.. Are the rad hoses warm or do they feel cool after the car runs for a bit (be careful, or you can check them with a pyrometer)? If they feel or are cool, it’s likely the thermostat.

EDIT: I checked a couple of FSMs for the charts for diagnosing this code. Step 1 in both is “replace thermostat.”

[Natasha]

[quote=”dtidman” post=160217]
EDIT: I checked a couple of FSMs for the charts for diagnosing this code. Step 1 in both is “replace thermostat.”[/quote]

Correct. Hence, my whole question. Checking both the CTS and thermostat is trivial, but “a lot of work” in sense that I have to get brand new gaskets for the thermostat and doing either of these requires me to replace the coolant again (which again adds the risk of introducing air into the system).

[quote=”dtidman” post=160217]Air id the cooling system usually leads to overheating, the P0128 is an under temp[/quote]

Yes, but just as an engine running without oil will show lower temperature on the gauge, I am wondering if air in coolant can cause the same effect?

[Dave Tidman]

I have not heard of air in the cooling system causing a low temperature issue. Not saying it can’t happen though.

A possible quick test is possible (with some risk if your radiator hoses are old and brittle) using tools like this (http://www.harborfreight.com/automotive-motorcycle/hoses-lines/3-piece-line-clamp-set-97578.html, don’t slag me for harbor freight, it was the quickest example I could find). You could clamp off the hose that leads to the thermostat and watch the temperature gauge and see if the temp goes up. Just watch carefully and unclamp if the temp hits a normal range. In essence, you are a manual thermostat.

IIRC, (been a while since I owned a Honda, but I did have a 1999 civic), there are 3 temp sensors, one for the gauge, one for the ecu and one to turn on the fan. I’m assuming the cooling fan does not run. Also, I assume your cabin heat is tepid.

[Justin]

9/10 times a p0128 is going to be a thermostat. If you can find someone local with an “airlift” coolant refill tool that will save you the headache of burping the system. Use a clean bucket and capture your coolant, and reuse.

Sent from my iPhone using Tapatalk

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