Check engine light on, thermostat not working properly

Hi,

The vehicle isn't reaching operating temperature within a predetermined amount of time, so it becomes an emission issue and sets a code. Is the code you are getting a P0128? Let me know that.

Now, here is the issue. The temperature sensor is signaling a certain temperature. We need to determine if what the PCM is receiving is correct. By chance, do you have an infrared thermometer? If you do, with the engine cold, remove the radiator cap, start the engine, and allow it to reach operating temperature. Next, using an infrared thermometer, check the temperature of the coolant being circulated in the radiator.

The most common causes are the things you already addressed, so there could be an issue with the wiring. Also, make sure the cooling fans are not turning on.

Let me know. Also, let me know if I have the correct code and if there are any others stored.

Take care,

Joe

Hi,

Happy to help. Let me know what you find. Also, if you can think of anything that could help diagnose the issue, let me know. It's important that you take notice if the cooling fans are coming on early. That could be causing an issue. However, if the thermostat stays closed, it should still warm up to operating temperature.

Hang in there. We'll get it figured out.

Take care,

Joe

Hi,

Then the sensor isn't working properly. If it was boiling, then it certainly was over 212F. I have a feeling it's a wiring issue.

Since the sensor is new, I suspect we have a corrosion issue to contend with. The signal to the gauge/computer is basically based on the amount of voltage allowed to pass through the sensor. The voltage changes a caused by temperature. If there is excessive resistance (due to corrosion or a connection), it will cause the signal to be off.

Here is what I suggest: First, disconnect the connector at the sensor. There will be two wires on the connector, one is violet with an orange tracer and the other is dark blue with a dark green tracer.

The dk blue/ dark green wire provides a ground for the sensor. Check for continuity to ground. While checking it, move that wire around to see if there is a change in resistance.

Next, with the key on, check the other wire violet/orange wire for power. Let me know what voltage is found.

This is where to start. At this point, I have a theory related to the integrated power module but don't want to jump to conclusions. In addition to checking the wiring, inspect the connector. Make sure there is no corrosion, and the connector pins are not pushed back or damaged in any way.

Here is a link you may find helpful:

https://www.2carpros.com/articles/how-to-check-wiring

Let me know if you are comfortable performing the tests or if you have other questions.

Take care,

Joe

See pic below.

Hi,

If you got a direct replacement connector, you should be able to just use the lock mechanism on yours. That way you won't have to cut anything.

I noticed you mentioned a code. What code did you get?

Joe

Hi,

Yep, that code indicates the vehicle isn't reaching operating temperature fast enough or not at all. Let me know what is found with the wiring testing.

Take care,

Joe