Question about 2004 Chevrolet TrailBlazer

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P0128 Code for a 2004 trailblazer with service engine soon light

I went to auto zone said code p0128. I checked Coolant ok. no leaks no cound.. Could it be the thromostat? and if so how do i repair it..

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  • Chevrolet Master
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Replacing it is the only fix. Sounds like it may be sticking open slightly.

Posted on May 27, 2009

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I have a 04 trailblazer check engine light was ongot it checkednumber 1 misfireI just replaced the cords and plugs so I took me 1 off put it on 2 the check engine light went off got home put the code...


code p0128 refers to coolant thermostat--coolant below thermostat regulating temperature==causes mechanical fault. ( thermostat stuck open --replace it) If you are experiencing cold weather then there is a problem with the ecm settings as the ecm should be compensating for the cold ambient temperature and setting the fuel mixture to richer than normal ( same as using a choke). Check the fault codes again and check for a coolant sensor fault.

Oct 31, 2014 | 2004 Chevrolet TrailBlazer

1 Answer

2004 trailblazer code po128


P0128:
P0128 OBD-II Trouble Code
Technical DescriptionCoolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

What does that mean?This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.

CausesA code P0128 may mean that one or more of the following has happened:

Low engine coolant level .
Leaking or stuck open thermostat .
Faulty cooling fan (running too much) .
Faulty coolant temperature (ECT) sensor.
Faulty intake air temperature (IAT) sensor .Here's a link on replacing your thermostat.

Feb 06, 2013 | 2004 Chevrolet TrailBlazer

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Got codes from auto zone po128 &po506


P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125

In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.

Symptoms: You will likely not notice any drivability problems other than the MIL illumination.

Causes: A code P0128 may mean that one or more of the following has happened:
Low engine coolant level
Leaking or stuck open thermostat
Faulty cooling fan (running too much)
Faulty coolant temperature (ECT) sensor
Faulty intake air temperature (IAT) sensor

Possible Solutions: Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:
Verify coolant strength & level
Verify proper cooling fan operation (check if it's running more than it should). Replace if necessary.
Verify proper engine coolant temperature (ECT) sensor operation, replace if necessary.
Verify proper intake air temperature (IAT) sensor operation, replace if necessary.
If the above items check out good, replace the thermostat
If Nissan vehicle, check for Technical Service Bulletins (TSBs), as the ECM may need to be reprogrammed to correct the P0128 code


P0506 - Idle Air Control (IAC) System RPM Lower Than Expected

This P0506 code is one that's sometimes triggered on vehicles that have electronic throttle control. That is, they don't have a regular throttle cable from the accelerator pedal to the engine. They rely on sensors and electronics to control the throttle. In this case, the P0506 DTC (diagnostic trouble code) is triggered when the PCM (powertrain control module) detects an engine idle speed that is lower than the desired (pre-programmed) RPM.

Potential Symptoms: Most likely the only thing you'll notice is the idle speed is lower than normal so it will likely be rougher. There are potentially other symptoms as well. Of course, when trouble codes are set, the MIL (malfunction indicator lamp, a.k.a. the check engine light) illuminates.

Causes: A P0506 DTC trouble code may be caused by one or more of the following:
A vacuum leak
An air restriction in the intake air path or exhuast
A faulty positive crankcase ventilation (PCV) valve
Damaged/failed/dirty throttle body
Internal engine problem
Failed PCM

Possible Solutions: This DTC is more of an informational code, so if there are any other codes set, diagnose them first. If there are no other codes, inspect for vacuum leaks, restrictions, and damage. If there are no symptoms other than the DTC itself, just clear the code and see whether it returns.


Check it, and keep us updated.

Apr 20, 2011 | 2004 Ford F150

1 Answer

My service engine soon lght is on in my 2004 chevy trailblazer LT. i went to take the care through marta this morning so i can renew my tags for my car. the man told me that the trouble sensors are P0014...


The P0014 code refers to one of your camshaft position sensors being out of time with the other. Does not mean its bad but it could be. The P0128 code refers to your engine running cooler than it should. Your coolant thermostat may be stuck open not letting the engine warm up to it's proper temp. Now you did not say which engine you have in the TrailBlazer. There are 2 different engine used in the year model. Please repost with that info.

Feb 01, 2011 | 2004 Chevrolet TrailBlazer

3 Answers

What can keep causing Check engine code P0128


CODE P0128- THERMOSTAT MALFUNCTION. POSSIBLE CAUSES 1. ECT SENSOR IS OUT OF CALIBRATION. 2. CHECK THE OPERATION OF THE THERMOSTAT IT MAY BE STUCK OPEN.3.INSPECT FOR LOW COOLANT LEVEL OR FOR AN INCORRECT COOLANT MIXTURE.

Jan 06, 2010 | 2004 Kia Spectra

2 Answers

My engine light is on and the faulty code is P0128, what is this mean?


Trouble Code: P0128

Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)
Possible Causes:


Insufficient warm up time Low engine coolant level Leaking or stuck open thermostat Inoperative engine coolant temperature (ECT) sensor Inoperative Cylinder Head Temperature (CHT) sensor

Dec 04, 2009 | 2004 Ford Focus

2 Answers

Check engine light on, diagnostic code 0128 and 0410 keep coming up


P0128 - Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature)

P0410 - Secondary Air Injection System Malfunction
(has to do with exhaust system)

Note: There is a technical service bulletin (TSB) regarding code P0410 for a number of GM models. The TSB calls for the replacement of the AIR pump and the installation of a new secondary injection hose.

Oct 13, 2009 | 2005 Chevrolet TrailBlazer

1 Answer

P0410 Secondary air injection system fault, P0128 Coolant temp


most ecu controlled vehicles have a 'limp home'mode if 2 or more fault codes are stored,it is designed to get your attention before damage is caused and to get you to the nearest w.shop to fix,i would have codes cleared and retest vehicle,it is the cheapest and 1st option for any shop,some late models even have excessive mileage past service interval in the 'limp' program

Jul 24, 2009 | 2004 Chevrolet TrailBlazer

2 Answers

P0172 and P0128 Error Code 2003 Trailblazer 4WD


PO172 means that an oxygen sensor in bank 1 detected a rich condition (too little oxygen in the exhaust). I would replace the thermostat first. The computer could be injecting too much fuel because it thinks it never gets to operating temperature. That may keep the light off.

Jan 28, 2009 | 2003 Chevrolet TrailBlazer

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