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CODE P0128 - How To Fix What it Means on 2005 Liberty
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=88&t=87905		 Page 1 of 1
Author:  Liberty for All [ Mon Mar 12, 2018 12:09 am ]
Post subject:  CODE P0128 - How To Fix What it Means on 2005 Liberty
P0128 CODE came up on my diagnostics. It means something is wrong with the Cooling System but I replaced the Thermostat less than two years ago when I flushed the coolant and replaced the hoses. Low miles since then so have any of you had trouble with Thermostats breaking? I read sometimes this code can mean one or two sensors are bad. If so, where can I locate those sensors on the engine? Ideas about what else it could be?
I put on a new water pump, good quality, three years ago.
Author:  Scar0 [ Mon Mar 12, 2018 5:45 am ]
Post subject:  Re: CODE P0128 - How To Fix What it Means on 2005 Liberty
Diesel or gasser?
All I have is info for 06, so it may be slightly different then the 05.
P0128-Engine coolant temp sensor
Engine is cold to long.
Or
P0128-Thermostate rationality
What does your temp gauge say on the cluster? Is it in the normal range?
To bad you KJ guys don't have outside temp displayed on the cluster.

Low coolant, bad thermostat, Bad/shorted engine coolant temp sensor and/or wires, Bad/shorted Ambient air temp sensor and/or wires, and a few more.

Engine coolant temp sensor.
Front center of engine, front of intake manifold 3.7.
Not 100% sure on the CRD but looks to be center of the left side of the head.
Ambient air temp sensor is in the front of the engine compartment. Usually located behind the grill/bumper.(Left side?)

Always disconnect the Neg(-) battery cable and isolate it, before you work on your rig.

BTW; This is the KK section of Lost, But we will try to assist anyway. :wink:
Author:  Liberty for All [ Mon Mar 12, 2018 6:16 pm ]
Post subject:  Re: CODE P0128 - How To Fix What it Means on 2005 Liberty
This is a Gasser 3.7L. Why my signature is no longer displayed below post now, IDK?
Gauge on dash shows right in the middle.
I reposted on KJ area. I thought I had deleted this post.
Thanks, but I want to know if anyone has taken the steps you listed to save time and cash.
Can you test sensors w/o removing them?
How?
Author:  Scar0 [ Tue Mar 13, 2018 3:07 am ]
Post subject:  Re: CODE P0128 - How To Fix What it Means on 2005 Liberty
If the engine operating temp gauge is reading in the middle, odds are that is not where the problem is.
The Ambient air temp sensor can't really be tested unless it is in a controlled climate. Ideally at a temp of 68 Deg F.
At 68 Deg, the sensors resistance should be between 10,000 and 13,000 ohms.
Author:  tjkj2002 [ Tue Mar 13, 2018 9:08 am ]
Post subject:  Re: CODE P0128 - How To Fix What it Means on 2005 Liberty
Scar0 wrote:
If the engine operating temp gauge is reading in the middle, odds are that is not where the problem is.
The Ambient air temp sensor can't really be tested unless it is in a controlled climate. Ideally at a temp of 68 Deg F.
At 68 Deg, the sensors resistance should be between 10,000 and 13,000 ohms.

For the KJ when that temp needle is in the middle that only indicates the coolant temp is between 178 degrees and 229 degrees.
Author:  Scar0 [ Tue Mar 13, 2018 8:05 pm ]
Post subject:  Re: CODE P0128 - How To Fix What it Means on 2005 Liberty
tjkj2002 wrote:
Scar0 wrote:
If the engine operating temp gauge is reading in the middle, odds are that is not where the problem is.
The Ambient air temp sensor can't really be tested unless it is in a controlled climate. Ideally at a temp of 68 Deg F.
At 68 Deg, the sensors resistance should be between 10,000 and 13,000 ohms.

For the KJ when that temp needle is in the middle that only indicates the coolant temp is between 178 degrees and 229 degrees.

Which means the coolant temp is being transmitted from the sensor to the PCM and other computers which need it.
If that reading stays constant(once it reaches the middle) while the rig is being driven in normal conditions, this is a good indication the coolant temp sensor and related circuits are working. Not saying it is perfect, but at least it is working. So that would, at least, eliminate the connectors and wires involved with the coolant temp sensor as the problem. Yes, the coolant temp sensor could still be a contributing factor if the reading it not dead on spec. Or if it is covered in crud, causing the true reading to be delayed.
Author:  tjkj2002 [ Tue Mar 13, 2018 9:58 pm ]
Post subject:  Re: CODE P0128 - How To Fix What it Means on 2005 Liberty
Scar0 wrote:
tjkj2002 wrote:
Scar0 wrote:
If the engine operating temp gauge is reading in the middle, odds are that is not where the problem is.
The Ambient air temp sensor can't really be tested unless it is in a controlled climate. Ideally at a temp of 68 Deg F.
At 68 Deg, the sensors resistance should be between 10,000 and 13,000 ohms.

For the KJ when that temp needle is in the middle that only indicates the coolant temp is between 178 degrees and 229 degrees.

Which means the coolant temp is being transmitted from the sensor to the PCM and other computers which need it.
If that reading stays constant(once it reaches the middle) while the rig is being driven in normal conditions, this is a good indication the coolant temp sensor and related circuits are working. Not saying it is perfect, but at least it is working. So that would, at least, eliminate the connectors and wires involved with the coolant temp sensor as the problem. Yes, the coolant temp sensor could still be a contributing factor if the reading it not dead on spec. Or if it is covered in crud, causing the true reading to be delayed.

Your not getting the fact that at dead center(temp guage) the coolant temp is somewhere between 178 degrees and 229 degrees,half that range is "under normal operating temps".

The t-stat can open early(or stuck open) and you will reach 178 degrees but in say 20mins instead of 10mins for a t-stat that does not start to open till 195 degrees like it is supposed to.

In over 20 years I have never ran into 1 vehicle with that code that the temp sensor was the issue,that's hundreds(if not thousands) of vehicles that I've diagnosed with that code.

Even some cooling systems with dual coolant temp sensors when one temp sensor goes bad it always sets a different code and not P0128.
Author:  Scar0 [ Wed Mar 14, 2018 3:41 pm ]
Post subject:  Re: CODE P0128 - How To Fix What it Means on 2005 Liberty
tjkj2002 wrote:
Your not getting the fact that at dead center(temp guage) the coolant temp is somewhere between 178 degrees and 229 degrees,half that range is "under normal operating temps".

The t-stat can open early(or stuck open) and you will reach 178 degrees but in say 20mins instead of 10mins for a t-stat that does not start to open till 195 degrees like it is supposed to.

In over 20 years I have never ran into 1 vehicle with that code that the temp sensor was the issue,that's hundreds(if not thousands) of vehicles that I've diagnosed with that code.

Even some cooling systems with dual coolant temp sensors when one temp sensor goes bad it always sets a different code and not P0128.

Thank you for confirming it is not likely the coolant temp sensor that is the issue. As I loosely said in the first post of mine you quoted.
"If the engine operating temp gauge is reading in the middle, odds are that is not where the problem is."
Then followed up in the second post of mine you quoted.
"Which means the coolant temp is being transmitted from the sensor to the PCM and other computers which need it."
"this is a good indication the coolant temp sensor and related circuits are working. Not saying it is perfect, but at least it is working." "So that would, at least, eliminate the connectors and wires involved with the coolant temp sensor as the problem."

At no point did I say the problem was the engine coolant temperature sensor. Both you, and I know, only a test could verify that for sure...

Liberty for All, in post 1, asked specifically what sensors were involved.
So that was the main question I addressed. But that was not all I addressed.
Liberty for All asked;
"I read sometimes this code can mean one or two sensors are bad. If so, where can I locate those sensors on the engine?"
I answered both those questions.

Liberty for All, also asked;
" Ideas about what else it could be?"
If you see my first post in this thread, I mentioned several things that could be the cause. Including the thermostat.
"Low coolant, bad thermostat, Bad/shorted engine coolant temp sensor and/or wires, Bad/shorted Ambient air temp sensor and/or wires, and a few more."

In Liberty for All's second post he asked about testing the sensors.
The first post of mine you quoted addressed that question as well.

So I'm not sure what your trying to say, that I haven't already said.

If I am interpreting your posts correctly;
I believe you have been hinting around that it is likely a problem with his thermostat, But haven't out right said it.
If that is the case, a simple post similar to, "It is probably a problem with your thermostat.", would have sufficed.
Which would have made all the rest of these posts unnecessary, and there would have been no comments or arguments from me about such a post...
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