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Old 10-26-2011, 05:01 PM   #1 (permalink)
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p0128 problem

How do i diagnose this problem, i know it that the coolant temperature is too low. How do i get to the bottom of it.

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Old 10-26-2011, 05:37 PM   #2 (permalink)
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2005 chevy impala 3.4, 126,000 miles, replaced thermostat and coolant temp sensor less than a year ago

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Old 10-26-2011, 08:40 PM   #3 (permalink)
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sounds like a stuck open thermostat to me. is the coolant full? any leaks or anything?

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Old 10-26-2011, 08:48 PM   #4 (permalink)
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DTC P0128
Circuit Description
An engine coolant temperature (ECT) sensor monitors the temperature of the coolant. This input is used by the powertrain control module (PCM) for engine control and as an enabling criteria for some diagnostics.

The air flow coming into the engine is accumulated and used to determine if the vehicle has been driven within the conditions that would allow the engine coolant to heat up normally to the thermostat regulating temperature. If the coolant temperature does not increase normally or does not reach the regulating temperature of the thermostat, the diagnostics that use ECT as enabling criteria may not run when expected.

This DTC will only run once per ignition cycle within the enabling conditions. If the PCM detects the calibrated amount of air flow and engine run time have been met, and the ECT has not met the minimum thermostat regulating temperature, DTC P0128 sets.

Conditions for Running the DTC
DTCs P0101, P0102, P0103, P0112, P0113, P0116, P0117, P0118, P0125, P0502, P0503 are not present.
The startup ECT is less than 75C (167F).
The intake air temperature (IAT) is more than -7C (+19F).
The engine run time is between 30-1,800 seconds.
The vehicle is driven more than 0.8 kilometers (0.5 miles) at more than 8 km/h (5 mph).
Conditions for Setting the DTC
The PCM detects that:

The calibrated amount of engine run time has been met.
The calibrated amount of engine air flow has been met.
The calibrated vehicle speed and distance have been met.
The calibrated ECT of 80C (176F) has not been met.

that means a bad thermostat or engine coolant temperature sensor.

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Old 10-26-2011, 10:08 PM   #5 (permalink)
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Just replaced radiator, coolant sensor, and thermostat less than a year ago. There are no leaks that I know of. Coolant level is good.

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Old 10-26-2011, 10:19 PM   #6 (permalink)
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unplug the battery to rest the light. then drive it and see if it comes back on. check your temp gauge to see what it reads.the t-stat or sensor could have messed up again. what kind are they?

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Old 10-26-2011, 10:35 PM   #7 (permalink)
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I do not remember what brand they were, I bought both at autozone. The temp gauge is broken in my car, it always fluctuates, sometimes it goes all the way around the dash.

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Old 10-27-2011, 06:50 AM   #8 (permalink)
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OBD-II Trouble Code: P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

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Old 10-27-2011, 01:51 PM   #9 (permalink)
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We have a 2002 3.4 that throws that code randomly, I just clear it and let it ride. Its not consistent, so I don't worry.

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Old 10-27-2011, 02:02 PM   #10 (permalink)
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I have this problem currently, so far replace the coolant temp sensor (mechanic told me) cause everyday after 10 min of driving when temp needle gets to one line before halfway the temp gauge drop to dead cold, but if I clear then pending code (engine light not on yet) the gauge goes back to normal and the engine fan turns off. thinking about replacing the IAT and if fails replace the thermostat.

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Old 11-01-2011, 04:36 AM   #11 (permalink)
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sorta same problem

i sorta have the same problem
needle workds then i reset code by disconnecting battery terminals...and then needles working for fine for awhile after that...i just replaced temp sensor cuz i thought that was the problem but i never tried to reset the code wit old sensor...so not sure if i bought a sensor for nothing....also i was wondering if when u needle drops..does ur AC quit blowing cold?

that is what happend wit mine..so im constantly disconnecting my battery i live in tx and its hot without ac plus car only has one fan right now so i need to keep an eye on temp

feed back please anyone


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Originally Posted by systemcheck2006 View Post
I have this problem currently, so far replace the coolant temp sensor (mechanic told me) cause everyday after 10 min of driving when temp needle gets to one line before halfway the temp gauge drop to dead cold, but if I clear then pending code (engine light not on yet) the gauge goes back to normal and the engine fan turns off. thinking about replacing the IAT and if fails replace the thermostat.

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Old 11-01-2011, 05:41 AM   #12 (permalink)
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my ac works ish (it is like 40 degrees out) this weekend im hoping to replace thermostat, never done it before (alittle low on funds) gonna do it myself.

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Old 11-01-2011, 05:48 AM   #13 (permalink)
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well if its 40 degrees out u wouldnt know for sure unless u check if the clutch is engaging

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Old 11-14-2011, 07:28 AM   #14 (permalink)
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replaced thermostat this weekend, everything working perfectly now.

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Old 03-23-2012, 11:37 PM   #15 (permalink)
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i know this is super old but i still having the same problems...so u just replaced ur thermostat? and everything worked fine afterwords?

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