2004 Grand Prix non sc, P0128, help please

cambridge

Newbie
Joined
Jan 18, 2008
Messages
4
Points
0
Hi

Recently I scanned a trouble code P0128. Seemed pretty straightforward, I replaced the thermostat. Check Engine came up again with the same code (after clearing original). Next, I did the next obvious thing and replaced the Coolant temp sensor. I didn't reset the code just to see what would happen. After a couple of cycles, the check engine light went off, so I figured that I fixed the problem. However, it came back on AGAIN with the same P0128! I noticed two things: 1) when the weather is warmer, the light just goes off by itself, but soon as it gets colder the light (and same code) come back, 2) when it's colder it seems to take the gauge longer to get to op temp, i. e. I'll be driving for a long while and it stays at 1/4, after a while it goes to mid to slightly past and the fan kicks on as normal.
I would really appreciate some feedback.
Thanks
 

wap

GO MOUNTAINEERS
Joined
Nov 24, 2006
Messages
153
Points
16
Age
120
Location
SUMMERSVILLE, WV
before the po128 tripped the mil light, did you have any service performed on the car, say like, flush and fill the radiator? or, did you recently change the thermostat prior? if so, I have seen this code as a result of a too strong mix of antifreeze. pure antifreeze with no water will 'suck' all of the heat out of the engine and take to the radiator. Dexcool is the antifreeze of choice here. is it very cold where you live? do you run the car on defrost all of the time? what temp range thermostat did you use? should be 195 degree or approximate. make sure you did not get a high-flow performance thermostat. several possibilities, but if you check the coolant and it checks for -50 below, drain some out and add distilled water. 2 qts at a time. most cars are more than good with a -20 below mix. post back....wap
 

kev2

wrench
Joined
Nov 14, 2006
Messages
4,919
Points
48
Age
120
vehicle is STOCK?

replacement T'stat was a 195*?
 

cambridge

Newbie
Joined
Jan 18, 2008
Messages
4
Points
0
Hi

Yes, the vehicle is totally stock. The Thermostat manufacturer spec 195. The system was flushed and filled this summer, by the dealer with dexcool. I've known these guys for a while and they're pretty much by the book. This fall the coolant was checked at around -40. Where I am, the it's cold, but not extreme, about -10C right now. It really seems like a cold weather condition, the MIL comes on and off (with P0128) when it warms or cools, weirdest thing. I know the cts works by a voltage read, but I would suppose it has to be relative to an actual ambient. Does the IAT sensor have anything to do with this????
 

kev2

wrench
Joined
Nov 14, 2006
Messages
4,919
Points
48
Age
120
yes* .......why do you ask?

*complicated - parameters for test use IAT
 

cambridge

Newbie
Joined
Jan 18, 2008
Messages
4
Points
0
Could a faulty IAT be responsible for a bad read of the CTS, i. e. it malfunctions in the cold, when the CTS sends voltage read to PCM, because of the bad IAT read, calculation of coolant temperature fails PCM test - then throws the code? It warms up, the IAT works normally.
Maybe I'm reaching.
 

Gus

wrench
Joined
Dec 8, 2006
Messages
2,421
Points
36
If the coolant if the right mix, I'd try another another thermostat...was it a dealer OEM stat?
 

kev2

wrench
Joined
Nov 14, 2006
Messages
4,919
Points
48
Age
120
I would agree with GUS ..........trying an OEM T'stat to many, here me included, have been plagued by this seemingly simple part......

There are no modifications - fresh air? K&N ? no other codes? fans not on constsnt?

A look at the freeze frame would answer question about IAC intermitant...
 

wap

GO MOUNTAINEERS
Joined
Nov 24, 2006
Messages
153
Points
16
Age
120
Location
SUMMERSVILLE, WV
classic too stong of a mix. most antifreexe straight of of the bottle, pure is between 40 and 50 below. dexcool very rarely comes pre mix, at least in my experience. 2 qts out, 2qts of distilled water in. do you think he needs to get 'oe' distilled water? lol. in a very cold climate or very cold conditions, the proper mix is crucial for the coolant to ramp up to temperature quickly. maybe you need move to an 'oe' climate. sorry guys, I have a bad 'oe' sense of humor. good luck cambridge.
 

Gus

wrench
Joined
Dec 8, 2006
Messages
2,421
Points
36
A 50/50 mixture of DEX-COOL® and clean drinkable water will provide the following protection:

Notice: Pure coolant can be added to raise the boiling point of the coolant, but too much will affect the freezing point. Do not use a solution stronger than 70 percent, as the freeze level rises rapidly after this point. Pure coolant will freeze at -22°C (-8°F).
Give freezing protection down to -37°C (-34°F).
Give boiling protection up to 129°C (260°F).
 

cambridge

Newbie
Joined
Jan 18, 2008
Messages
4
Points
0
Some excellent feedback, thanks. Everythings OEM, except the climate I suppose! The air coming out of the vents is quite hot fairly soon after start, though the gauge remains relatively low. Also I felt the therm housing after a drive and it seems to be hot enough, too hot to really grab. I never thought of the mix though, just figured techs a the dealer ship would try to keep it standard. This does make sense though considering it seems to be a cold weather condition only. I guess I'll live with until spring and then drain and fill myself with some of that "OE" distilled water (maybe the way things are going for GM it's just a matter of time for this part).
I appreciate everyones time in their responses, excellent.
Regards
 
Top