Question about 2003 Chevrolet TrailBlazer

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P0172 and P0128 Error Code 2003 Trailblazer 4WD

I am reading an error code P0172 System too rich (Bank 1) and P0128 Cooland Thermostat (coolant temperature below thermostat regulator temp). The engine appears to idle and run fine; however, the service engine soon light continues to alternate on and off. I have an inline 6 engine on a 2003 Trailblazer LT 4WD. The engine has just over 112k miles.

The fan clutch is clicking while attempting to engage. I believe I need to replace the fan clutch and based on error P0128, a new thermostat.

Any additional suggestions

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  • rburnsc Feb 11, 2009

    I went to get my 03 trailblazer inspected. Failed because of an error code to do with my thermostat. I appreciate the advise about the O2 sensor in case this does not fix the problem. Now I have to figure out how to get to the thermostat.

  • Anonymous Mar 16, 2009

    diagnosed with code ? for T-stat. Replaced T-stat, however, service engine light still coming on. Brought to a different Chevy dealer and diagnosed the same. Tech had to "relearn" t-stat for it was not set properly. Service engine light intermittent. Seems to do better in warm weather. Temp gage varies/fluctates during driving. Will reach approximately 210 on warm days and the light goes off. Previous tech has suggessted a cam phaser change though not sure if this will cause the light to stay off.

  • Anonymous Mar 18, 2009

    Same exact problem with my 04 Envoy.

  • Anonymous Apr 01, 2014

    clutch wont engage even when the engine is up totemperature

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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.

Posted on Jan 28, 2009

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  • Master
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The po172 is the 02 sensor, replace that. I would change the thermostat first, before the fan clutch and see if it is still doing it, then go after the fan clutch.

Posted on Jan 28, 2009

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I have a 2006 Buick Lucerne V6 code po128 comes up. What does it mean?


P0128 BUICK P0128 BUICK - Engine Coolant Temperature Below Thermostat Regulating Temperature Repair Importance Level: 3/3 Repair Difficulty Level: 2/3 help.jpg Share facebook.png twitter.png linkedin.png google-plus.png sep.png print.png pdf.png share.jpg 3 comments.png ' Add Comment xicon.jpg http://www.autocodes.com/p0128_buick.html Forum Code Possible causes - Leaking or stuck open thermostat
- Low engine coolant level
- Insufficient warm up time
- Faulty engine coolant temperature sensor
- Engine coolant temperature sensor harness is open or shorted
- Engine coolant temperature sensor circuit poor electrical connection
help.jpg What does this mean? Tech notes If cooling system is not leaking and the fluid level is OK, replacing the thermostat usually takes care of the problem.
help.jpg What does this mean? When is the code detected? If the Powertrain Control Module (PCM) detects the calibrated amount of air flow and engine run time have been met, and the Engine Coolant Temperature (ECT) has not met the minimum thermostat regulating temperature, the code P0128 will set. Possible symptoms - Engine Light ON (or Service Engine Soon Warning Light) P0128 Buick 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 diagnosis. 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 diagnostic that use ECT as enabling criteria may not run when expected.



Read more: http://www.autocodes.com/p0128_buick.html#ixzz3vprh5jzz

Regarding which thermostat to use, I am guessing it depends on where you live.

Ask these people when you order the thermostat.

http://www.autopartswarehouse.com/shop_years/buick-lucerne-thermostat-2006.html

Dec 30, 2015 | 2006 Buick Lucerne

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4 Codes in computer


code p0128 indicates a mechanical fault ( could be the thermostat stuck open)
code p0174 -system too lean -bank2 ===causes --intake /exhaust leak--fuel pressure/pump--injectors--AIR system--hose connection/s
code po171 refers to system too lean bank 1 same as po174 with the HO2S sensor being the culprit. As to all being related . only by way of the o2 sensors
code p0442 is not connected to the first 3 as it is in a different section of the fuel system

Apr 09, 2014 | 2003 Saturn VUE

4 Answers

Po128 is the code. What's the problem


Well, I can't give you any specific information regarding your vehicle because you forgot to mention what kind of vehicle you have. (This is kinda important if you really want some help figuring out what is wrong with your car)

The "Generic OBD" of code P0128 is "Coolant Temperature Below Thermostat Regulating Temperature"

The most likely cause is a stuck-open thermostat, however, I have also seen defective Engine Coolant Temperature (ECT) sensors also cause this code.

Jun 13, 2011 | Chevrolet TrailBlazer Cars & Trucks

1 Answer

The check engine light goes on and then off. Had Autozone scan code and it read P0420 and P0128. Any ideas what this means?


You don't mention any vehicle specific info, but the codes read as follows:

P0420 - "Catalyst Efficiency Below Threshold (Bank 1)"

P0128 - "Coolant Temp Below Thermostat Regulating Temp"

I'd guess you basic problem is the engine isn't getting hot enough in normal operation.

Try replacing the thermostat. Do be aware that you have to purge the cooling system of any trapped air for proper cooling system function. Some vehicles have 1 or more air bleed screws in the system to aid in this process.

I suspect that if you resolve the P0128 DTC, the other will go away (might have to clear the code and go thru requisite drive cycle.

Jan 02, 2011 | Chevrolet TrailBlazer Cars & Trucks

2 Answers

P0128 coolant temp below thermostat/regulating temp


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

Hope helps (remember to rate and comment this).

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1 Answer

What do codes P0128, P0133, P0496


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Definition of Diagnostic Trouble Code P0496 Category Powertrain Definition Evaporative Emission System High Purge Flow

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What can keep causing Check engine code P0128


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