Help explain this thrown code to me, please! [Archive] - GrandAmGT.com Forum

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2002GT
12-06-2004, 03:53 PM
My car threw an SES light..

TROUBLECODE OBDII (ALPHA) P CODE

TROUBLESHOOTING P0128:

The PCM has determined that the input from the coolant temperature sensor indicates a temperature value that is below the thermostat regulating temperature.


Can someone please tell me what the means. Also maybe what needs to be fixed, and how much? Thanks!!!

Gold99HO
12-06-2004, 04:18 PM
i think it might be a sensor.

when did it come on

how hot was the car, and how warm was it out side

2002GT
12-06-2004, 04:39 PM
the car was running normal temp... about 200... it was at night, kinda cold... i say 50's... i was going around 85-90 on I-95

EDIT: I left out a word

The PCM has determined that the input from the coolant temperature sensor indicates a temperature value that is below the thermostat regulating temperature.

Malaclypse
12-06-2004, 11:03 PM
Find someone with either a scanner or an infrared thermometer. Bring the car up to operating temperature and either check the temp of the thermostat housing or the temp reading of the ECT (prefferably both).

If the reading from the thermostat housing is around 130 - 150, your thermostat is sticking open.

The temperature "gauges" in most GM cars aren't really an accurate depiction of how hot your car is running. They're more like indicators. If you stray towards the red its time to shut it down. Since I installed my water temp gauge, I've noticed that from around 1/4 to just about half on my temp indicator is just below 210 no matter what.

H.O. Driver
12-07-2004, 05:42 AM
If you have warranty left, take it in. If not, I am guessing your T-Stat is stock open or your coolant temp sensor is shot and needs to be replaced. The sensor has been more of problem than a stuck t-stat on these cars, but every car is different.

2002GT
12-07-2004, 09:16 PM
Is it dangerous do not get this fixed immeditately if this is the problem?

I am about 150 miles from home... and it's finals week, and i have no time now

DarkKnight
12-07-2004, 09:31 PM
Well as long as it over cools rather than over heats you're fine. You'll have lower milage, but the car won't blow up if that's what your asking. On the other hand, if it over heats and the computer thinks it's cool, the fans won't come on. However, if you have plenty of coolant, and is't not 90* outside, you should be fine.

2002GT
12-07-2004, 09:36 PM
when i drive home i'll be going around 85-95 and it will be around 50* outside...

what did you mean... "You'll have lower milage" ???

dennistowell
12-20-2004, 02:33 PM
Ok well i have been having this same code throw for about a month now, really havnt worried about it since the car is running on the cold side and not running to hot. Well last night it threw it again and heres what the cumputer in the car saw when it threw the code. I have a Plam Pilot with a cable to connect to the port under the dash to read everthing from the computer and clear all the codes from the memory. This is all that i have been doing for like 4 weeks now, everytime the light would come on i would just turn it back off and ignore it since there seems to be not apperant danger to the car. so anyways this is all the stuff the car recorded when the light came on, it was about 11:00 Sunday night and it was like 45 degrees outside, i was on my way home from work i had only been driving for like 5 minutes and maybe 3 or 4 miles:

DTC Causing Freeze P0128
Vehicle Speed 56 MPH
Intake Manifold Pressure 25.2 inHg
Short Term Fuel Trim-B1 1.6%
Calculated Laod Value 24.3%
Engine RPM 1766 RPM
Engine Coolant Temp 162 degF
Long Term Fuel Trim-B1 -7.8%
Fuel System Status CLoop O2

Went and talk to the guys at auto zone and found out that it could be either a stuck thermostat or a bad coolant temp sensor, the guy said that replacments for both of those are around $10 each. I was just wnodering where the coolant temp sensor is and if it is very hard to replace? If any of those numbers help you guys, i would like to know which thing to replace first.

Malaclypse
12-21-2004, 12:08 AM
-Addition to my previous post-

I've seen this code four times in the past week. Every single time its been a thermostat sticking open. Don't worry about overheating because when the PCM sets this code, the fans turn on automatically because its unsure of the coolant temp. It'll also run the fans for 30 seconds to 1 minute after the car is shut off.

Go ahead and replace your thermostat. Its rare that I've seen a coolant temp sensor fail. The coolant temp sensors for GM are a wax pellet containing a resistor in a brass case. Not much room for malfunction.