P0128 CODE & CAN NOT RESET CHECK ENGINE LIGHT

Question edited for clarity and add a few spaces and capital letters. :>D
Question moved to model category.

That code is the opposite, it isn't REACHNG temperature it should. However, I had that code and changing the thermostat, got rid of the code.

Error code P0128 indicates that your engine coolant temperature is below the thermostat regulating temperature. This means that your Engine Control Module (ECM) or Powertrain Control Module (PCM) has recognized that your engine is running cooler than it's supposed to.

p0128 Code ' KBB - Kelley Blue Book

Videos in the link Julie.

https://www.google.com/search?q=Toyota+Highlander+Hybrid+Limited.+How+to+replace+thermostat

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Once a repair is completed, if the offending repair was the cause of the light it will go off on its own. I would scan for codes and see if they are related. If you just want to turn the light off and clear codes, disconnect the battery for ten minutes.

An OBD-II scan tool can do this.

When the Check Engine light comes on,you need to clear the code, either use a scan tool to clear the code or you can use 3 consecutive ignition cycle,that the diagnostic runs and not fails, Or A history of 40 consecutive warm up cycles if no failure are reported by this or any other emission relateddiagnostic, If the relacement thermostat and you cleared the close and this code appears You need to inspect the ECT sensor or even the ECT harness

Diagnostic Test Code (DTC) P0128 has a generic description of "Coolant Temperature Below Thermostat Regulating Temperature".

The Poertrain Control Module (PCM) checks the coolant temperature at startup. It then calculates the period of time that it should take for the engine to reach operating temperature (or thermostat regulated temperature). After the calculated period of time, the PCM again checks the coolant temperature. If it has not reached operating temperature, a code P0128 flag is set in mode 6.

If the engine still has not reached operating temperature after 5 more minutes of continuous engine operation, code P0128 is set in continuous memory and the Check Engine (or Malfunction Indicator Light "MIL" is turned on.

Possible causes:

> A stuck-open engine coolant thermostat (MOST common)
> A skewed Engine Coolant Temperature (ECT) or Cylinder Head Temperature(CHT) sensor (working, but not reading correct temperature)
> Low engine coolant level (causing the sensor to not read correctly)

First, the engine coolant (antifreeze) level should be checked. If it is low, it is recommended to perform a cooling system pressure test to find out WHY.

Then, the actual engine temperature should be measured with an infrared thermometer near the ECT or CHT. The reading from the thermometer should be checked against the live sensor data with a scan tool. (PLease note that MOST generic OBD code readers CANNOT perform this function.)

If the reading from the thermometer and the sensor data is within 10 degrees F of each other, replace the thermostat. Otherwise, the sensor circuit should be checked for high resistance (loose or corroded connector, damagd wire, etc.). If no high resistance is measured in the rest of the circuit, the sensor should be replaced.

Causes A code P0010 may mean that one or more of the following has happened:

• Faulty oil control valve (OCV)
• Open or short in the VVT/VCT circuit
• Open or short in the OCV / solenoid valve
• Damaged computer (PCM)

Possible Solutions Some recommended troubleshooting and repair steps are:

• Carefully inspect the Bank 1 VVT/VCT system circuit wiring and connectors, repair as required
• With a warm engine, test the operation of the OCV, replace/repair as needed

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 sensor ECT
  
• 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

P0641 is a generic code for a possible bad ECU. I would first fix the other two issues and then clear the check engine light and see if it comes back on. If it does, then you have a possible bad ECU and will need to run further tests to see if that is the case or not

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

Other ECT sensor and circuit related DTCs: P0115, P0116, P0117, P0118, P0119, P0125

Leave 02 sensor alone ,it is doing it's job . It is heated up because of lean fuel mixture due to incorrect engine temp.,replace thermostat before looking further.

There are TONS of reasons - the first , and least expensive, step is to read the codes that the onboard computer is throwing. Instead of spending a lot of money on a code reader, or wasting money by going to the dealership, find an AUTOZONE (or, sometimes MERCHANT's will offer a "we'll check your CHECK ENGINE LIGHT for free) and they'll give you a generic read of the code(s).
I say "generic" because the computer DOES throw specific codes; the "we'll do it free" places usually don't have the same kinds of super-readers that the dealerships or high-end repair shops own. But, bear with me for a sec....this may save you some money.
If the generic code says, "O2 sensor"....that's not as specific as you'd like (because there are multiple 02 sensors!)...BUT....if ONE sensor is not functioning properly, its a pretty good bet that the other(s) will be failing soon too, since they were all installed at the same time and all were made by the same company, etc.
The "generic" code WILL tell you enough info as to which sensor is bad (the one in front of the converter vs the one behind the converter) so....if THAT is the code, then simply replace both behind or both "in front". Follow?
Now, where you'll typically get the most common code is for low fuel pressure. If you've never changed your fuel filter...that's a good place to start. The "generic" code will indicate "fuel pressure". If you've never changed the filter....see? BUT, a fuel pressure problem could also be as simple as "loose gas cap"! If your generic code says "fuel pressure", then I'd reset the computer (disconnect the battery for a few minutes and re-connect), and while the battery is disconnected, make sure that the gas cap is tight and the little rubber gasket around the cap is in tact.
Keep in mind....a "check engine light" doesn't mean that your computer is throwing codes CONSTANTLY! It means that the computer sensed something at some point while the scan was running and SOMETHING got its attention. "IF" the fuel cap was loose, for example, just re-tightening it will not reset the "check engine light"! You gotta reset the computer (disconnecting the battery is easiest), THEN the light will be off. If the light returns, then the problem was something other than the gas cap.
Taking your time and doing a little on-line research can save you a ton of money! A 2000 is relatively easy to work on yourself...at least SOME of the issues...even if you're not a really techie-kinda person. Take the easy and inexpensive shots first....
Hope this helps.

po128 is a coolant temp sensor problem, check wiring to sensor if ok replace sensor,good luck.