My 2003 chevy trailblazer keeps throwing code

P0128 OBD II Trouble Code Coolant Thermostat Coolant Temperature Below...

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.

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

Sounds like the thermostat may be stuck open or has anyone put a colder thermostat in the car,because once it starts to get cold it will throw a SES with a colder then stock thermostat.

Code PO128; coolant temp below thermostat regulating temp. Replace the thermostat and that should address your issue.

Thank you for using fixya and good uck

First, you should check to see if there is a thermostat in the engine or if it is stuck open.

P0128 is coolant operating temperature operating too low. This can be contributed to the Thermostat stuck open or faulty electronic radiator fan clutch. This is common, I had the same issue and replaced the thermostat and fan clutch and had the clutch re-programmed (required) at the dealer. As for the P0410, check the air pump fuse, if blown it will set this code on. Also check the air pump hoses for water and cracks. Hopefully this helps!!

this is probably a bad thermostat

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.

The P0218 Code is primarily intended to indicate a faulty thermostat.
Have the thermostat replaced

Other possible causes that could trigger this code would be:
Low engine coolant level
faulty cooling fan
faulty coolant temperature sensor
faulty intake air temperature sensor

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.