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OBD-II code PO-128?

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Old Mar 3, 2008 | 08:28 PM
  #1  
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Unhappy OBD-II code PO-128?

...Coolant temp lower than thermostat temp.

had my service engine soon light on for some time now, finally got around to checking it out at autozone.

Guy said i need a coolant temp sensor, not a thermostat whats the diff. where is it located and how hard is it to replace? any help would be nmuch appreciated. SEARCHED, found nothing on this.

edit: ok i just searched on google and the code has to do with thermostat function??

does that guy not know what hes talking about, cause when i asked ok so i just need to change the thermostat, he says no its the coolant temp sensor, sounds like the same freakin thing to me
 

Last edited by ShanesG; Mar 3, 2008 at 08:32 PM.
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Old Mar 3, 2008 | 08:33 PM
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Backside water pipe. Number 4 on this diagram.
 
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Old Mar 3, 2008 | 09:42 PM
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so it would just be that sensor right?

i also read something about the thermostat may be stuck open or something?? (not a g35 though)
 
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Old Mar 3, 2008 | 11:06 PM
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Before you go replacing things, look for the obvious. Check coolant level in the reservoir. Also check coolant level in radiator with engine cold. Do NOT attempt opening radiator cap on hot engine. If coolant level is low and there is no coolant reaching the sensor, the sensor will read a low temperature since it will not be submersed in the coolant.
 
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Old Mar 3, 2008 | 11:31 PM
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+ 1. It is very rare for one of these thermostats to go. Even more rare for the sensor to go. It is possible, but really check things out first. The thermostat is right in the front of the engine - driver's side. It must be purchased with the housing ($ 70). It takes about 10 minutes to replace it.
 
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Old Mar 4, 2008 | 02:24 AM
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Originally Posted by Mr.GEE
Before you go replacing things, look for the obvious. Check coolant level in the reservoir. Also check coolant level in radiator with engine cold. Do NOT attempt opening radiator cap on hot engine. If coolant level is low and there is no coolant reaching the sensor, the sensor will read a low temperature since it will not be submersed in the coolant.
Thanks, but i know that already haha
i was just asking if anyone had this before new what the diff. was between the T-stat, and the coolant temp. sensor. I would never change anything untill i knew it was defective. Thanks for the help tough, much appreciated. Will check the coolant levels in the morning. Also this has been of for quite some time nowand and the coolant levels were fine before when the light was on, but ima check again!
 
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Old Mar 4, 2008 | 01:03 PM
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noone else has had this prob.? or code?

checked coolant, and its filled all the way
 

Last edited by ShanesG; Mar 4, 2008 at 01:05 PM.
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Old Mar 4, 2008 | 01:11 PM
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T-stat = mechanical valve that opens at a pre-determined temp to regulate the flow of coolant though the motor.

Temp sensor = an electrical based device that measures the temp of the coolant and sends that info to the ecu and/or gauge. Ecu uses that info for various functions:
a) To determine if the engine is cold (cold start mode) or warm enough to go into closed loop operation.
b) If the temp gets too high, it might swap to a conserative ign map.
 
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Old Mar 4, 2008 | 01:21 PM
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thx jeff
 
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Old Mar 4, 2008 | 11:46 PM
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ummm....here's the real answer, and troubleshooting...etc..

Rick

http://www.ismcentral.com/DTC/DTC_P0128.pdf
 
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Old Mar 5, 2008 | 12:14 PM
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^thank you so much rick ima check everything out this weekend
 
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Old Aug 21, 2009 | 08:10 PM
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Originally Posted by sliderg35
+ 1. It is very rare for one of these thermostats to go. Even more rare for the sensor to go. It is possible, but really check things out first. The thermostat is right in the front of the engine - driver's side. It must be purchased with the housing ($ 70). It takes about 10 minutes to replace it.
Is that a dealer price? I got a thermostat with housing and gasket for $20 at Checker Auto Parts. Same price at Autozone, but they didn't have in stock.
 
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Old Aug 21, 2009 | 11:23 PM
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I guess I got scr3wed. I got mine from the dealer. (All prices Canadian.)
 
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